Volume XIX No. 8 April 2008 1. Introduction N uclear fusion processes in our Sun provide 99.97% of Earth's total energy in a broad range of wavelengths. This article develops a simple model for Earth's equilibrium temperature resulting from incoming and outgoing radiation. Our atmosphere blocks the entry of higher energy (smaller wavelength) radiation like x-rays and gamma rays, and selectively permits entry of lower energy photons in the visible and infrared range to our surface. Earth, in turn, radiates energy outwards into space. These longer exiting wavelengths also traverse the atmosphere, encountering blockage from greenhouse gases. In our model, we'll assume that there are no atmospheric impediments to incoming and outgoing radiation energy. 2. Solar Structure Our Sun is a raging battleground between the gravity of its 1.99x1030 kg mass and the 6x1011 atmosphere pressure generated by fusion processes, converting its hydrogen to helium. This balance of forces has been going on since the Sun evolved about 4.5 billion years ago, and will continue, we hope, for at least an equal amount of time. As Figure 1 illustrates, the solar interior starts at the core where plasma temperatures reach 1.5x107 K, necessary for the fusion process to operate. Next, we have the radiation zone through which the core's high energy photons slowly migrate outwards. The convection zone acts like water in a kettle, as turbu-lent cells move plasma outwards. The photosphere is the densest layer of the Sun's atmosphere. It is the visi-ble part of the Sun and is the location of sunspots. Sunspots are highly magnetic cooler areas with tempera-tures ranging from 4,000 K to 4,500 K. Faculae, large areas hotter than the surrounding photosphere's 5,780 K temperature, are associated with sunspots. The next layer is the chromosphere. It is hotter than the photo-sphere and it has a reddish color. The corona is the Sun's outer atmospheric layer. Its near vacuum pressure has a temperature exceeding 106 K, and it extends for millions of kilometers. Continuing from the corona well beyond Neptune, the solar wind is mainly made up of protons and electrons and contains frozen-in magnetic fields. Both the chromosphere and the corona are visible during a total solar eclipse. Movement of plasma in the convection zone coupled with the Sun's differential rotation periods creates its magnetic field. The equator's 25-day versus the polar region's 35-day rotation times create magnetic eruptions on the photosphere, resulting in sunspots. Sunspot counts reach a maximum with cycles ranging from 9½ to 12½ years and averaging 11 years. Solar flares occur when magnetic energy in the chromosphere and corona is released. Flares generate huge amounts of energy mostly in the x-ray range. They are capable of hurling tremendous amounts of mass into space in the form of coronal mass ejections (CMEs), which can last from a few seconds to a few hours. 3. Sun's Energy Source At one astronomical unit, the Sun delivers an average of about 1,368 watts/m2 perpendicular to the Earth-Sun line, the so-called solar constant. In fact, the solar constant varies by 6.9%, being higher in January and smaller in June due to Earth's elliptical orbit. In addition, there is a small (0.1%) solar constant increase between maximum and minimum sunspot activity. At maximum, the reduced energy from the more numerous cooler sunspots is more than offset by that of the hotter faculae. The source of the Sun's energy wasn't clearly understood until before World War II. For some time, it was known that chemical sources weren't adequate. It's been estimated that if the Sun were made of gasoline and oxygen, it could provide necessary energy for only 10,000 years. In 1862, Lord Kelvin postulated that gravitational contraction was a possible source. Sufficient energy is created if the Sun contracts 20 meters/year, but its energy would last only 45 million years. He disagreed with geologists at the time who knew Earth was older than 45 million years. In 1938, the nuclear physicist, Hans Bethe, postulated the conversion of hydrogen to helium as the source of our Sun's energy and, for that, he was awarded the Nobel Prize in 1967. The Sun is mostly hydrogen: 91.2% by volume. When four hydrogen nuclei (protons) are converted to a helium nucleus, there's a loss of 0.7% mass. In other words, the four hydrogen nuclei are 0.7% more massive than the helium nucleus. This mass difference is converted to energy via Einstein's famous E = mc2 relationship. Thus, the Sun is gradually becoming less massive as it generates energy, by about 4.2 billion kg/sec. 4. Earth's Energy Balance Using basic blackbody physics, we'll now calculate Earth's approximate steady-state temperature. Solar ra- diation inflow and Earth's energy outflow will be utilized, but atmospheric greenhouse effects will not be considered. 4.1 Radiation/Temperature Relationships A blackbody is a theoretical object that absorbs all electromagnetic radiation that falls on it. In other words, it does not reflect light. Physicists determined exact blackbody temperature/ luminosity relationships useful in astronomy by the end of the nineteenth century. Astronomers often make the simplifying assumption that stars like our Sun behave like blackbodies. However, as Figure 3 illustrates, our Sun exhibits approximate, but not perfect blackbody energies at different wavelengths. Note that 1 nanometer = 10 angstroms. One reason for variations from the dashed blackbody curve is that not all photons originate exactly at the Sun's 5780 K photosphere. Emissions originating from different depths have different temperatures, and there-fore have different energies. An important radiation energy/temperature relationship for blackbodies is the Stefan-Boltzmann Law: (1) Where: F = energy in watts/m2 = Stefan-Boltzmann constant, 5.67x10-8 watts/m2/T4 T = temperature, K This relationship illustrates two important points: a) Everything above absolute zero temperature (K = 0° or C = - 273.15°), must radiate electromagnetic energy. For example, an average man has a body surface area of about 1.8 m2. Therefore, at room temperature (about 295 K) his skin radiates over 770 watts. b) Energy radiated varies as temperature to the fourth power. Doubling the absolute temperature increases radiated energy by sixteen. Another key blackbody radiation/temperature relationship is Wien's Displacement Law: (2) Where: = the maximum energy wavelength in micrometers, :m T = temperature, K With a 5,780 K temperature at the Sun's photosphere, the maximum energy wavelength is 0.501:m (501nm), which is in the visual range. On the other hand, at room temperature the skin on our body radiates at a maxi-mum energy wavelength of 9.82:m in the infrared range. 4.2 Earth's Equilibrium Temperature The Earth is not a blackbody. Significant solar radiation is reflected back into space. Figure 4 illustrates the complex incoming/outgoing energy interchange. The measure of a body's reflectivity is called its albedo. Black-bodies have a zero albedo. The Earth's prominent features like its oceans, land masses, clouds, etc. each have different albedo as illus-trated in Figure 5. Astronomers generally use a figure of 0.30 as Earth's average albedo. Therefore 70% of the Sun's incoming energy remains on Earth. Recall that the solar constant is 1368 w/m2. Therefore, given the Earth's 0.30 albedo, the amount of solar energy retained is 1368 w/m2 x 0.70, or about 958 w/m2. We can now predict the temperature of a blackbody Earth when it is in equilibrium, ignoring atmospheric interference. This occurs when the Sun's incoming radiation energy is equal to the Earth's outgoing radiation energy. The incoming radiation is captured by the cross- section area of the Earth, BRE2: 958 x (BRE2) watts (3) Where RE is the Earth's radius. Earth's outgoing radiation occurs over its entire surface, 4BRE2 at temperature equilibrium. Using Stefan-Boltzmann's Law (equation 1) its outgoing radiation is: (4BRE2) x (FT4) watts (4) By setting Earth's incoming radiation energy (3) equal to its outgoing radiation energy (4), we can solve for Earth's equilibrium temperature T. T = (958 / 4F)1/4 = 255K (5) The 255 K equilibrium temperature is about -10 F. It's generally agreed that Earth's actual average temperature is about 288 K (590 F). There are several reasons why our simplified calculation is 33°K smaller than the actual temperature: a) The Earth is not a blackbody. b) We ignored the effect of atmospheric molecules which prevent outgoing lower wavelength radiation from escaping, leading to the 288°K temperature. We are fortunate for the presence of greenhouse gases because life as we know it wouldn't be possible without them. Carbon dioxide is an essential fuel that plants need in photosynthesis. Also, since seawater freezes at 28.5°F, a frozen Earth is not consistent with human survival. Figure 6 shows the impact of these gases on incoming and outgoing radiation. Notice that water is by far, the most important greenhouse gas because it is so prevalent in the atmosphere. 5. Final Thoughts Climatologists have a difficult task attempting to accurately forecast future climate. Factors such as cloud and ocean behavior as well as changes in atmospheric molecular content over time are not well understood. For example, methane is a 25 times more potent greenhouse gas than carbon dioxide, and its atmospheric percentage is expected to increase with time. There are also unknowns relating to future solar activity. Many factors must be understood for accurate long-term forecasts. Recent publicity on global warming has bombarded the public about future climate possibilities. Most cli-matologists insist that man- made CO2 increases are the root cause for global warming. Some scientists feel that human-based CO2 increases could not be the major reason for global warming, and that solar effects have been understated. It's certain that radiation energy-changes from small solar constant variations would have only a very minor impact on Earth's temperature. However, cloud formation effects from changes in solar wind may be consequential. There appears to be a striking relationship between the Sun's activity, solar wind intensities, galactic cosmic ray (high speed protons) intensity, and cloud formation. Low solar activity results in smaller solar wind magnetic forces which permit more cosmic rays entering our atmosphere, thereby creating aerosols necessary for cloud formation. A multinational study in the year 2010 at CERN called CLOUD has been proposed to simulate cosmic rays in a cloud chamber, and assess the viability of cosmic ray/aerosol formation relationships. "We want to reproduce what happens in the atmosphere", said Jasper Kirkby, leader of the CERN CLOUD team. "We want to understand how you could get from a cosmic ray to a cloud droplet, and in which parts of the atmosphere this could be occurring". (http://www.swissinfo.ch/chi/swissinfo.html?siteSect=43&sid=7253462) Given the paucity of sunspots in the past year which is an indicator of lower solar activity, some concern has even been recently expressed on the possibility of global cooling. In the 12 months since January 2007, the average global temperature has dropped an anomalous 0.64°C according to NASA's GIIS and three other monitoring organizations. Most experts believe this was due to the influence of the current La Niña Southern Oscillation. In spite of this decrease, 2007 was still one of the warmest years in history. Short term changes like this can of course, be reversed. More data and research are necessary for a credible long range forecast of climate. 6. References http://aerosols.ucsd.edu/classes/sio217A_07/SIO217aLecture03b.pdf http://arxiv.org/abs/physics/0104048v1 CERN CLOUD project http://en.wikipedia.org/wiki/Albedo http://en.wikipedia.org/wiki/Greenhouse_effect http://sidc.oma.be/index.php http://solar.physics.montana.edu/reu/2004/sgaard/flare.html http://solar.physics.montana.edu/reu/2004/sgaard/structure.html http://wattsupwiththat.wordpress.com/http://www.shef.ac.uk/physics/ teaching/phy103/solspec.html http://www.swissinfo.ch/chi/swissinfo.html?siteSect=43&sid=7253462 http://zebu.uoregon.edu/1998/es202/l13.html Taylor, E. W., 2005. Elementary Climate Physics. Oxford University Press. Astronomy Day Saturday, May 10th The Observatory will open at 12 Noon. Talks are planned throughout the day and they will run approximately one hour including Q&A. There will also be solar viewing through the Hydrogen-alpha filter on the 10-inch tele-scope. We will have a dinner break from 5:30 to 7:30 pm, after which, the observatory will be reopened for additional talks and celestial viewing. Updated schedule of events is on the Special Notice page of our web-site. Stewart's Skybox by Stewart Meyers W hen I was deciding on a topic for this month's column, several ideas presented themselves. I could have gone with a piece about a possible resurgence of the Pluto circus inspired by AAI member Laurel Kornfeld's recent appearance on AAI member Karl Hricko's radio program, "Contours" where she opined that the Pluto horse was still alive enough for some more flogging. Another possibility was the numerous obstacles to interstellar flight. This would have been in response to Ronald Held's presentation at a recent convention. Held is an astrophysicist who is a gung-ho advocate of manned interstellar flight. But, I nixed those ideas and was going to do a piece about planetary rings, since Saturn is well placed for observation, and also because of a new discovery by the Cassini space mission. But some sad though poorly reported news intervened. On March 19th, Sir Arthur C. Clarke passed away at the age of 90 in a hospital in Colombo, Sri Lanka. Clarke was one of the great geniuses of the last several decades. While he is best known as a science fiction author, in my opinion one of the top three of modern times (the other two being the late Isaac Asimov and the late Robert A. Heinlein) and is considered the most prophetic one since Jules Verne, he was also a noted sci-ence writer who wrote a large number of books and essays on science, mainly relating to astronomy and space. Yet, despite his long and distinguished career, Clarke's death received limited notice in the mainstream media, especially in broadcast news, an area of media that was largely made possible through one of his early ideas. Print media and the Internet did a better job. Clarke, his career, and accomplishments deserved a better tribute. Perhaps some day, someone will make a documentary about his life and work. While his achievements are too numerous and significant for a mere col-umn in an astronomy club newsletter to do full justice, this tribute will focus on just a few of them. Glide Path Sir Arthur C. Clarke was born in Minehead, England in 1917. While a boy, he discovered two things that would have great influence on his life: astronomy and science fiction. In his youth, Clarke made a few small refractors using cardboard tubes and old lenses through which he started looking at the night sky. This interest would stay with Clarke for the rest of his life. Then, in 1928, he came across his first science fiction magazine. He soon started reading all the science fiction he could get his hands on, including the works of Jules Verne, H.G. Wells, and later Olaf Stapledon. In 1939, World War II broke out in Europe, and, in 1941, Clarke joined the Royal Air Force. This would also be very influential to him and would also lead to one of his first contributions to society. While in the RAF, Clarke learned about electronics and engineering. One of the major issues facing the RAF in the war was safely landing planes when the weather was poor. One early solution essentially was to set a row of fires on each side of a runway. This would heat the air and prevent fog from forming. Besides the obvious safety prob-lems, this approach also wasted lots of fuel that was desperately needed for the war effort. Clarke was on a team that found the solution, a system called Ground Control Approach, which was the forerunner of the mi-crowave landing system used at airports throughout the world. So, when your plane lands safely at the airport on a cloudy, foggy night, you can thank Sir Arthur. Clarke wrote accounts of his RAF experience in a number of his non-fiction works. A fictionalized version can be found in his only non-science fiction novel, "Glide Path". Wireless World World War II also inspired another great Clarke idea - - his most famous one. During and after the war, people in Europe were frustrated by the poor quality of communications service between Europe and America. Shortwave radio had long range but is dependent on the variable ionosphere. Transatlantic cables had what today would be called limited bandwidth. In 1946, Clarke wrote a paper that was published in the magazine Wireless World in which he offered a solution. The paper proposed that radio communication between conti- nents could be greatly aided if a relay station could be placed in orbit around the Earth. The desired orbit was a circular one at the equator with an altitude of 22,300 miles. An object in such an orbit would complete one orbit in the same amount of time it takes the Earth to rotate once. Therefore, the satellite would appear to hover at about the same point in the sky as seen from the ground. If this sounds familiar, it should. It is the first detailed description of a communication satellite in geosynchronous orbit. That is why Clarke was considered the father of the communication satellite. However, Clarke himself admitted that he was not the first to conceive of the idea of a geosynchronous orbit (Konstantin Tsiolkovskiy was) and that German scientists Herman Oberth and Herman Noordung first mentioned communications with satellites in geosynchronous orbits back in the 1920's. However, Tsiolkovskiy's work was little read outside Russia and it made no mention of radio or communica-tions. Oberth and Noordung's papers, which were pretty much published only in Germany, advocated using mirrors and signal lights instead of radio (the long distance radio equipment of the 1920s was considered too bulky and unreliable). Their papers did not go into any great detail. On the other hand, Clarke's paper was the first very detailed discussion of the use of satellites in geosynchronous orbit for radio communication appearing in a publication that had international circulation. So the claim that Clarke invented the idea of the communica-tion satellite is still valid. While prophetic, Clarke was a bit off on some aspects of the communication satellite. His work in electronics was with vacuum tube technology (transistors would not be invented until 1947). And from his experience in the RAF, he knew that it took quite a bit of work to maintain the early electronics. Clarke first imagined the communication satellite as something akin to a space station with a human crew to maintain the relay equip-ment. By the time it was feasible to launch satellites higher than low Earth orbit, electronics and miniaturization had advanced enough to make Clarke's vision of manned relay stations obsolete. But the basic idea of the communication satellite remained valid. So, anyone who makes use of modern telecommunications has a rea-son to thank Sir Arthur. Naturally, Clarke's interest in spacecraft did not end with communication satellites. He had joined the British Interplanetary Society (BIS) (http://www.bis-spaceflight.com/) in 1934, and was a very active member (except for the time of his military service). His involvement with the BIS, as well as his dry sense of humor, inspired one of his earliest short stories which was a parody about a society like the BIS. It told of their comic misadven-tures when they decided to put some of their ideas into practice. Getting back to Clarke and the real BIS, in 1954, he took part in a debate about manned interplanetary flight. Clarke and his fellow BIS member Val Cleaver took the position in favor of it, and his opponents were none other than the author, C.S. Lewis (who wrote the "Narnia" series of books), and J.R.R. Tolkien of "Hobbit" fame. Lewis based his opposition of inter-planetary flight on a belief that it would allow mankind to spread sin to other worlds - a theme of the reli-gious/science fiction "Perelandra" trilogy that Lewis wrote. All These Worlds Are Yours Except Europa While much of Clarke's writing that is of interest to amateur astronomers and others who enjoy space sci-ence were the books and essays that he wrote which explained how space travel would work, his science fic-tion frequently delved into the nature of what was in space. Sometimes, their science was later found to be wrong, such as in his story "The Star" (1955) in which a Catholic astronaut visits an alien star system whose civilization was destroyed when its sun became a supernova that was seen on Earth as the Star of Bethlehem. Stars that can go supernova have life spans too short to develop habitable planetary systems. And, in "A Fall of Moondust" (1961), a layer of lunar dust, deep enough to swallow spacecraft, plays a prominent role. But most of those errors could be explained by the fact that Clarke was basing his tales on the knowledge of as-tronomy at the time they were written. As will be seen below, when he got things right, he really got things right. Probably Clarke's most famous work of science fiction was "The Sentinel". In this story, astronauts on the Moon come across a pyramid-shaped structure. All attempts to open it are unsuccessful and they eventually resort to explosives. This triggers a signal from the object. "The Sentinel" would form the basis for "2001: A Space Odyssey", one of the greatest films of all history. Clarke and Stanley Kubrick wrote the screenplay. The sometimes turbulent collaboration between the two men was well documented in the book "The Lost Worlds of 2001" which also includes samples of alternate versions of the story. Another source is the diary Clarke kept while working on the film. It has been converted to an online version and can be read at http://www.visual-memory.co.uk/amk/doc/0073.html. Clarke then wrote the novelization of the screenplay (using the version where the monolith is on Iapetus, instead of in orbit around Jupiter as it was in the film) as well as the sequel novels "2010", "2061", and "3001". Watching "2001", especially on DVD, it is amazing to see how accurate the space hardware appears. This is because Clarke knew enough about how spacecraft work to advise Kubrick on those matters. The scene in "2001" where Bowman boards the Discovery through an airlock without a space helmet was an example of where Clarke's knowledge was utilized in the film. Clarke knew that, based on research conducted by space agencies, the human body would not explode if exposed to space. He also realized that, if one prepared for it, they could have some seconds of functional time while exposed to a vacuum. And of course, Clarke also knew that noise cannot propagate in space, so the scene was silent, something that surprised many viewers. Also, to the credit of Clarke and Kubrick, no effort was made to show the moons of Jupiter in great detail since nobody really knew what they were like at the time. As a result, the scenes of the Discovery in the Jovian system still look reasonable today. About the only major error in "2001" was the timetable. However, that was not Clarke's fault. Because of his knowledge of the Apollo program (he was a consultant for CBS News during the Apollo 11 mission), he was aware of how developments in spaceflight progressed. So, Clarke simply assumed that space exploration would continue at the same pace it did during the Apollo era. That did not happen. What could be Clarke's greatest act of science fiction prophecy can be found in "2010". Inspired by informa- tion from the Voyager missions, the story has a Chinese expedition arriving at Jupiter while a Rus-sian/American mission is investigating what happened to the Discovery and Dave Bowman. The Chinese land on Europa and discover the hard way that there is an ocean full of life beneath the cracked ice crust. This was published shortly before the idea of a subsurface ocean and possibly life on Europa was widely accepted in the science community. However, we will have to wait decades for a probe to reach the Europan ocean to see if Clarke guessed correctly about life on Europa, though the idea of a subsurface ocean is the consensus view in science today. 1984: Spring Even after "2001" and "2010", Clarke still had a few prophetic tricks up his sleeve. As early as his 1967 book "The View From Serendip", a collection of essays about science, writing science fiction, and life in Sri Lanka, Clarke predicted a system where people would have consoles in their homes and offices which would use communications networks to distribute information, images, and eventually video information. Sound familiar? Clarke pretty much described the Internet, back when DARPANet (the ancestor of the Internet) was still being planned by the Department of Defense. Yet, in a later book, "1984: Spring", Clarke seems to downplay the Internet and he believed that the use of personal wireless communications devices would spark revolutionary changes in society. While ruling out the Internet was wrong, he was right about the communications devices. Today, we call them cell phones. And Clarke was extremely accurate in his prediction that many nations would be very reluctant to restrict them (Clarke believed that attempts to restrict them would alienate business people and be bad for the economy). For instance, the US government has always nixed legislation that would have allowed businesses to employ cell phone jamming technology, even though lots of people would like to see it in places like restaurants, schools, and theaters. Clarke's view on cell phones was no doubt influenced by his work advising Sri Lanka and occasionally India on communications issues. In those countries, telephone cables are expensive and frequently, in rural areas, are stolen and sold for scrap. Wireless technology with cheap, mass-produced cell phones would get around those problems. And his fictional prophecy also continued. In 1999, Clarke co-wrote the novel "The Trigger" with Michael Kube-McDowell, which depicted a 21st century climate of intense security and fear of terrorism within the United States, a full two years before the September 11th attacks. However, the terrorists in the story were American right-wing Christian white supremacists, not Middle Eastern Muslim radicals. The Last Theorem In 1987, Peter Diamandis, Todd Hawley, and Robert Richards founded the International Space University (ISU) (http://www.isunet.edu) in Strasbourg, France to better educate tomorrow's space policy makers. By 1989, the ISU needed a chancellor, and Arthur C. Clarke was named to the position. Despite having to do his job via long distance phone and video from his home in Sri Lanka, he held the post until 2004. Clarke also served as chancellor of the University of Moratuwa in Sri Lanka from 1979 to 2002. A full listing of all the posts he held, as well as the many scientific and charitable organizations he was involved with can be found at the website for the Arthur C. Clarke Institute for Modern Technology (http://www.accimt.ac.lk/darthur.html). In the 1990s Clarke's health seriously declined as a result of Post-Polio Syndrome. However, his mind was still sharp, and he continued to write stories, essays, and he even worked on some documentaries. One of his final TV appearances was as host of "The Colours of Infinity", a documentary about fractal geometry. He also wrote works in collaboration with other authors, partly to reduce his workload, partly to pass on his techniques. His final book, "The Last Theorem", a collaborative effort with Frederik Pohl, will be published later this year. One of Clarke's last acts on Earth was to review the final draft of the manuscript. Even as his health was failing, he continued to pursue astronomy, eventually observing the Moon and plan-ets on a video monitor using a camera hooked up to a remote control Schmidt-Cassegrain on the roof of his house. He kept observing until he was too ill to do so. In addition to his interests in science, Clarke was also a humanitarian. Throughout the time he spent in Sri Lanka, he never used a rickshaw because he did not believe that humans, regardless of race, should be beasts of burden. And, in "The View From Serendip", Clarke recounts how he always treated his servants fairly, even the ones who probably did not deserve it. At his 90th birthday, when asked what his three wishes for the future were, one was for the end of the civil war that has raged in Sri Lanka since the 1970s. Maybe his passing might inspire the Sri Lankans to make that wish come true. When this great man passed away, too much of the world failed to take any real notice. Mainstream broadcast news, which benefits considerably from the very communication satellites that Clarke foresaw, gave only short little blurbs or, in many cases, just a mere sentence on the crawling message at the bottom of the screen. Entertainment news outlets gave even less notice, evidently forgetting about his involvement in "2001". Print media did better, but most papers just ran the wire service copy of his obituary without adding any further commentary. NASA, an agency that benefited greatly from Clarke, was absolutely silent, probably because many who truly appreciated Clarke and would have had the class to honor him were no longer working there. The Internet was a far different story. Tributes and commentaries about Clarke and his works sprouted throughout the online world. People praised his writings as well as his vision. Finally, it seems that perhaps the universe itself honored him. On March 19th, no less than four gamma ray bursts were detected, a new world record. And one of these bursts was truly a whopper with an optical after-glow that may have peaked at between magnitude 5 and 6, another record that was set that day. Seems Sir Arthur might have received the cosmic version of a 21-gun salute. Though mainstream media might have hardly mentioned his passing, he has left his mark on popular cul-ture, mainly through the film "2001". Scenes from the film have been referenced and parodied in everything from newspaper comic strips, "Monty Python's Flying Circus", the Mel Brooks film "History of the World Part I", "Futurama" (they parodied both "2001" and "2010" in one episode), the "Stone Trek" Internet cartoon series, (http://www.angelfire.com/fl/sapringer/STONETREK.html), and even "The Simpsons". While some might argue that those references and parodies were tributes to Stanley Kubrick (Kubrick does deserve some credit), it should also be remembered that, if it wasn't for Clarke, there would have been no "2001", period. He was one of only a few authors to have that kind of influence on popular culture. Fortunately, the work of Sir Arthur C. Clarke is preserved. All his science fact articles can be found in "Greet-ings, Carbon Based Bipeds!: Collected Essays", 1934-1998 Edited by Ian T. MacAuley (c). "The Collected Sto-ries of Arthur C. Clarke". is a volume devoted to all of his short stories. Both are well worth reading. Then there is the large number of books he has written. Clarke may be gone, but he will be remembered as long as there are literate, intelligent people on Earth, and eventually far beyond it. What If The Earth Spun In The Opposite Direction? On those Fridays when he is not conducting his Fridays At Sperry presentations, Dr. Lew holds free seminars for AAI members. Here's his report from one such session. Why not sit in on one of these seminars? Several times at our seminar, we have considered hypothetical situations just to highlight how much our lives depend upon the Earth behaving as it does. One such session investigated what would happen if the Earth rotated in the opposite direction; that is from east to west. There are certain immediately obvious results. They are: 1) the Sun would rise in the west. 2) the fixed stars would rotate clockwise around the North Celestial Pole. 3) We would have prevailing easterly winds in the temperate zones. 4) Time zones would be in reverse order; i.e. London time would be earlier than New York time. 5) Cyclones would rotate clockwise in the Northern Hemisphere. All these events immediately come to mind, but there are several relatively obscure effects which would also occur. These are: 1) Labrador would become warm and eastern Europe colder. This is because the North Atlantic Gulf Stream would move northwest. 2) Hurricanes would occur in eastern Europe rather then western USA for the same reason 3) A reverse spinning Earth would subtract energy from the Moon causing it to spiral closer to the Earth 4) Lunar tides would increase for the same reason. 5) Warmer Japan and colder northwest USA since the Japanese current would flow northwest. What's Your Point of View? By Jeremy Carlo A ncient peoples associated certain traits with the sky's "wanderers" (translated from Greek as "planets") based upon their observed properties. The innermost planet, which quickly zips across the sky but never strays far from the Sun, came to be associated with Mercury, the fleet-footed Roman messenger god. The second planet, whose brilliance at magnitude -4 to -5 alternately dominates the morning and evening skies, was paired with Venus, the goddess of love, fertility and beauty. The red planet was identified with Mars, the war god, and a 'fixed' star with similar appearance was named Antares, the rival of Ares (Mars' Greek counterpart). And so on. While color is solely an attribute of the planet's surface characteristics, other properties - how it moves through the sky, how bright it appears, how much that brightness fluctuates over time, and so on - depend not only on the intrinsic properties of that planet, but also from where it is being viewed. I recently started to think about what the solar system would look like as viewed from other members of the solar system, and came to some pretty surprising conclusions. The View From The Moon Let's travel first to our nearest neighbor. Since the Moon is only about 1/100th the distance from the Earth as even its nearest neighboring planets, Venus and Mars, the solar system looks essentially the same from the Moon as it does from the Earth, except that instead of seeing the Moon in the sky, they see the Earth. While parallax differences cannot be neglected if you want to be accurate, they are rather small and (aside from rare exceptions such as transits or Mercury or Venus which may be visible from one but not the other) don't contrib-ute to vast changes in the sky's appearance. But there are a few significant differences between the view from the Moon and the view from the Earth. Since the Moon has no atmosphere, in addition to the obvious problems in breathing, there are several observational consequences. (To answer the eternal question: No, your eyes won't bulge out like Arnold Schwarzenegger in Total Recall.) Most importantly to a putative lunar astronomer, there is no air to scatter Sunlight, so stars are visible during the daytime! As long as we take care not to point the telescope at the Sun, and find a way to shield our eyes so they can dark-adapt, we can do serious observing at any time of day or night, with the "day" being about equal to a month in length, due to the Moon's slow rotation. The Earth would appear to be some 2 degrees across, 4 times the Moon's angular diameter from a terres-trial perspective, since the Earth is about 4 times larger in diameter than the Moon. That is large enough that one could make out the shapes of large continents, the polar icecaps and even large cloud systems (particu-larly the one that hangs around New Jersey on weekends) with nothing but the naked eye. Telescopically, a wealth of detail would be visible - one could make out large islands, land features such as peninsulas, and even large lakes. All but the largest manmade structures would be invisible to amateur-sized telescopes, how-ever. The Earth would go through the same phases as we see for the Moon - new Earth, crescent Earth, first quarter Earth, gibbous Earth, full Earth, and back to new. These phases would be staggered 2 weeks with re-spect to the terrestrial view of the Moon's phase; new Earth would happen at the same time as full Moon, and last quarter Earth would be simultaneous with the first quarter Moon. The Earth, moreover, would not move across the sky, but rather hang in roughly the same position while everything else drifts behind it. This is because the Moon is in a spin-orbit lock, and perpetually keeps the same face pointed toward the Earth. From any position on the Moon, the Earth remains stationary for all time, aside from small drifts due to libration, the Moon's wobbling with respect to this fixed position. And from half the Moon's surface (the far side), the Earth would not be visible at all. In fact, an observer who spent their entire life on the far side of the Moon might not even know that the Earth exists. What about eclipses? As seen from the Earth, there are two types of eclipses. Solar eclipses occur when the Moon's dark silhouette passes between us and the Sun. A lunar eclipse occurs when the Earth casts its shadow on the Moon. It turns out that what we see as a solar eclipse would be described as a lunar (a better term would be "Earthly") eclipse from the Moon, and what we perceive as a lunar eclipse is what lunar observ-ers would call a solar eclipse. But there are several significant differences between eclipses as observed terrestrially and those seen from the Moon. Since the Moon's shadow is not nearly big enough to fully block the Earth, you'd see (with a telescope) an inky dark spot which over the course of several hours would drift across the Earth's disc, quite similar to a shadow transit of one of Jupiter's Galilean Moons, except that you're standing on the object that is casting the shadow. A terrestrial observer standing in that blackened spot, of course, is at that moment within the Moon's umbral shadow and is witnessing a total solar eclipse. A larger but far less apparent penumbral shadow would also be seen to cover the regions where terrestrial observers see a partial solar eclipse. By sheer coincidence, from the Earth's perspective the Sun and Moon subtend nearly the same angle of sky, so the Moon's silhouette fits almost precisely over the Sun's disc during a solar eclipse. With the Sun's brilliant photosphere neatly concealed, the delicate corona can be seen during the few minutes of totality. If the Moon is farther from the Earth than usual, it's not quite big enough to completely cover the Sun, and we have an annular eclipse, in which a thin ring of Sunlight peeks out from around the Moon's limb. But the Earth's sil- houette is 4 times larger than the Sun as seen from the Moon; what would occur when the Earth passes in front of the Sun is usually described by astronomers as an occultation. Aside from perhaps a short time at the beginning and end of totality (which itself would last several hours) when a portion could be glimpsed, the corona would be essentially invisible, rendering the lunar observer's view of a solar eclipse somewhat less spectacular than it is from the Earth. But the dark disc of the Earth would be surrounded by a thin ring of reddish atmosphere-refracted Sunlight, casting a dim ruddy illumination across the lunar surface; this refracted light is the origin of the blood-red Moon that we observe in the totality phase of a lunar eclipse from the Earth. Now that we've seen what the sky looks like from our nearest neighbor, let's take a trip to some of our plane-tary companions. But first we should understand some of the most important factors in the observed behavior of a planet. A note on Pluto: I will assume Pluto to be a full-fledged planet for the purposes of this article, both because including Pluto leads to some interesting conclusions, as well as for my own personal safety from AAI's pro-Pluto faction! (Just kidding.) The Ecliptic The planets orbit in roughly the same plane. In other words, if you extended an imaginary plane outward from the Sun's equator, all the planets' orbits would lie within a few degrees of that plane. The sole exception is Pluto, whose orbit is inclined 17 degrees. At second place is Mercury, at only 7 degrees of inclination, with the other planets all within 5 degrees or less. The chief observational consequence is that from any of the planets, the other planets (again, with Pluto ex-empted from both cases) will appear to be strung out along an imaginary line across the sky known as the ecliptic. Inferior vs. Superior Planets Also crucial is whether the observed planet orbits more closely or farther from the Sun than the home planet. This, of course, is a relative phenomenon. From Mercury, all the planets are farther away. From Neptune or Pluto, the other seven planets are all closer (Neptune and Pluto behave toward each other in a more complex way, to be discussed in the second part of this article next month). A planet whose orbit is wholly contained in your planet's orbit, an inferior planet, is constrained to stay within a maximum angular distance along the ecliptic from the Sun, known as a greatest elongation. Further, at the time of greatest elongation, since the side we see is about a quarter of the way around from the side facing toward the Sun, we see a roughly "half-Moon" appearance. An inferior planet makes its closest approach when it is between you and the Sun; this is known as inferior conjunction. Since we see only the "nighttime" face of the inferior planet in this configuration, we see it only in silhouette, as during a transit. Slightly away from inferior conjunction, we see a thin crescent, but of course observation is difficult due to its proximity to the Sun's glare. We see the fully-lit face of the inferior planet when it is on the opposite side of the Sun; once again it is lost in the Sun's glare. This configuration, when the inferior planet is also at its maximum separation from the Earth, is known as superior conjunction. Therefore, the best period to observe an inferior planet is at or near greatest elongation, when it appears (from our perspective) farthest from the Sun; by following the planet as it courses from one conjunction to the next we can witness the inferior planet go through a full sequence of "phases." A planet whose orbit is larger than our own is known as a superior planet, and its behavior is much simpler. Its closest approach occurs when we are directly between it and the Sun. At that point the superior planet is at its biggest and brightest, and appears directly opposite the Sun's position in the sky, which is why this is called an opposition. Conveniently, at opposition, the superior planet is well-placed for observing all night long. From our terrestrial vantage point, Saturn was at opposition on February 24th, and Jupiter will reach opposition over the summer. Mars is currently receding from its most recent opposition in December 2007. When a superior planet is 90 degrees around from our position, this is called quadrature. Since we're seeing the planet from a different angle than the Sun "sees" it, we see a rather gibbous phase; this is generally only noticeable from our perspective in the case of Mars since the orbits of Earth and Mars are rather similar in size. Finally, when the superior planet is on the opposite side of the Sun, this is known as superior conjunction, in analogy with the same configuration for an inferior planet. And just as in the case of the inferior planet, the superior planet is at its maximum distance, and thus minimum size, at superior conjunction, and is also lost in the Sun's glare. Now we're ready to begin our tour of the solar system. First Stop: The View From Mercury To start off on the most obvious point, Mercury is much closer to the Sun than is the Earth. For this reason, the Mercurian year is only 88 Earth days long. Mercury's rotation is, however, rather slow and only completes one rotation relative to distant stars every 59 days. Its rotation axis is inclined nearly zero degrees from the ecliptic, which means it doesn't experience seasons for the reason that the Earth does; from any given point on Mercury, the Sun will traverse the same course across the sky every single six-month-long solar day (the solar day is a function of both the orbital period and the rotation period, and in this case is not nearly equal to either). But Mercury, like the Moon, has no atmosphere, meaning that we can observe during both night and day. It also means that Mercurian ground telescopes are not limited by atmospheric turbulence, and large-aperture instruments can, like orbiting Earth observatories, function to diffraction-limited performance. The final point to note is that Mercury has a very elliptical orbit, carrying it from 0.31 to 0.47 astronomical units (AU) from the Sun. This is significant enough that there are observationally significant differences between when Mercury is at perihelion and aphelion. The sky, as one would expect from this location, is ruled by the Sun. While from the Earth the Sun shines at magnitude -26.7, from Mercury the Sun would appear to be magnitude -28 to -29, depending on Mercury's distance from it. Instead of a 30' disc as seen from the Earth, from Mercury the Sun's bloated disc would sub- tend from 1.2 to 1.7 degrees, approximately three times larger in diameter. Due to Mercury's highly eccentric orbit, the Sun does not move smoothly across the sky. In fact, when Mer-cury is at its closest approach to the Sun, its orbital angular velocity exceeds its rotational angular velocity, so the Sun appears to move retrograde (i.e. west to east) across the sky. From either of two spots on Mercury, one of which is known as Caloris Planitia (Latin for "the hot plain"), the Sun is straight overhead when Mercury is at perihelion, so this retrograde loop occurs near the zenith, giving rise to an extra long, hot day - the Sun rises in the east to the zenith and a little past it, then stops, reverses back across the zenith, stops again, then continues traveling in the original direction until setting in the west. From some other points on the surface the retrograde motion occurs when the Sun is near the horizon, giving days that have two Sunrises and two Sun-sets! Mercury has no Moon, which considerably diminishes the richness of the Mercurian sky. But this loss is miti-gated by the absolute brilliance of Venus, which would shine at opposition at a magnitude of approximately -7, comparable in brightness to our view of the crescent Moon! To the naked eye, Venus would be a brilliant white starlike point, and the brightest object in the sky aside from the Sun. Telescopically, Venus at opposition would present a nearly featureless white disc some 40 to 65 arc-seconds in diameter. As a superior planet to Mercury it would not show any phases aside from a stout gibbous phase near quadrature (somewhat like Mars as seen from Earth). What about the Earth? To the naked eye the Earth would appear as a pale bluish star at a magnitude of -5, second only to Venus in sheer brilliance. To a sharp-eyed observer (preferably with some sort of neutral den-sity filter to cut down on the glare) the Earth would be joined by the Moon, itself of opposition magnitude -1, and some 13-17' from its parent planet. Telescopically, the Earth/Moon system would be the showpiece of the Mercurian sky. At opposition the Earth's disc would be 25-32" across, comparable to our view of Mars at an ideal opposition, while the Moon would by 6-8". Both would fit within a medium-power eyepiece field and be simultaneously resolved as fully illuminated or gibbous discs. It would be possible to identify the largest conti-nents and polar icecaps on the Earth at this distance, and even the Moon would display some subtle shading. Mars, in contrast, would be rather disappointing. With a maximum brightness of magnitude -1 (compared to -2.5 to -3 from the Earth), it would be a far less imposing naked-eye sight, especially overpowered as it is by Venus and Earth. Since Mars doesn't come nearly as close to Mercury as it does to the Earth (0.89 AU versus 0.38 AU), Mars' disc never exceeds 11" in size, less than even the poorest apparitions from Earth. Only the largest features, such as the polar caps and Syrtis Major, would likely be visible in amateur- sized instruments. But it would come to opposition every 3 months or so, in contrast to the two-year delay between its terrestrial oppositions. The outer planets look more or less the same as they do from the Earth, except that there is somewhat less of a difference between opposition and superior conjunction. Jupiter's maximum angular diameter would be about 43", versus 48 as seen from the Earth, and would be about half a magnitude dimmer. The rest of the planets would show even less of a discrepancy. They would, however, reach opposition about once every 3 months, some four times more frequently than as seen from the Earth. From Mercury everything seems to move a whole lot faster than we're used to, except for the Sun, which takes its sweet time. Second Stop: The View From Venus With our Mercurian observing tour done, let's get in our spaceship and head out to Venus. The first point to note is that as inhospitable to humans Mercury seems, it's an observer's paradise compared to Venus. Venus is perpetually enveloped by opaque clouds, and the surface temperature is a consistent 750 degrees. (Kelvin, not that it makes much of a difference.) Images returned by (rather short-lived) Soviet landers indicate the sky is probably a uniformly drab yellow-orange color due to scattered Sunlight. But if we were to set up on Venus' surface with a telescope that could see through the clouds (and come on, the public knows we can do that), we'd notice two very strange things. Firstly, the solar day is about 117 Earth-days long. The Sun shines at magnitude -27.5, and its disc subtends an obtuse 45' . Further, since Venus ro-tates in retrograde (opposite in sense from the other planets), everything would rise in the west and set in the east! Like Mercury, Venus has no Moon. And from Venus, Mercury is a rather more interesting planet to observe than it is from the Earth. From the Earth, Mercury can get no more than 29 degrees from the Sun, which means that simply observing Mercury is somewhat of a challenge even for the experienced observer. Seeing it requires quite a bit of advance preparation, not only in selecting the right place to observe (clear, unobstructed horizon), but also the right time (about an hour after Sunset or before Sunrise, when Mercury is near greatest elongation, with the ecliptic coming up from the horizon at a favorable angle for your latitude). But from Venus, Mercury can get up to 40 degrees from the Sun, making detailed observation possible. It would be significantly brighter than as seen from the Earth, at times perhaps up to -4 in magnitude, and its disc would subtend 6" at superior conjunction and up to 24" at inferior conjunction (the equivalent numbers from the Earth are 5 and 12). From Earth few, if any, real surface features on Mercury can be seen, owing both to the small apparent size of Mercury's disc as well as its invariably low altitude, but from Venus a wealth of subtle detail should be detectable. The Earth would be an even more spectacular sight than from Mercury, and would dominate the Venusian sky. Its opposition magnitude would be -6.5, and its disc would subtend up to 70" (nearly 50% larger than the terrestrial view of Jupiter). At this scale even an amateur-sized instrument would reveal many fine details - large weather patterns would be visible, and distinctive land features such as India, Florida and the tip of South America would be clearly detectable. The Moon would itself shine at about -2.5, separated by up to half a de-gree from the Earth; with the naked eye (and a "Moon filter" to cut down glare) it is possible to follow the Moon's path around the Earth over the course of a month. Through a telescope both could be simultaneously viewed at low power, and the Moon's disc at opposition would be up to 16" across, comparable to a typical poor terrestrial opposition of Mars; some of the maria would be detectable at this distance. Mars is again somewhat disappointing, although not as much so as from Mercury. Its maximum brightness would be almost -2, and at opposition its disc would range from 10-16" in diameter (compare to 14 to 27" as seen from the Earth). The outer planets, once again, look pretty much the same, somewhat intermediate between the familiar Earthly experience and the more muted behavior we saw from Mercury. Next Stop - Mars After visiting the last three alien worlds, we may take some comforts in the view from Mars. Mars rotates with a period slightly under 25 hours, making the Martian day (called a sol) rather similar in length to what we have at home. Its rotation axis is tilted about 25 degrees to the ecliptic, so Mars has seasons just like the Earth, although its year is about twice as long. We might be tempted to call the seasons super-winter (average temperature -70 degrees F) and super-duper-winter (-100 degrees F or colder). Interestingly, it is now technologically possible to do some basic astronomy from the surface of Mars with the cameras aboard the Mars rovers Spirit and Opportunity. In this respect, Mars is unique among all the other planets in this tour. Indeed an article entitled "Astronomy on Mars" has recently arisen on Wikipedia. Mars has a rather tenuous atmosphere. It's not enough to breathe, but enough to scatter Sunlight, filling the daytime sky with a ruddy brown glow. The Sun's disc is some 19 to 23' in diameter, variable due to the considerable eccentricity of Mars' orbit, and shines at a magnitude of -25.5 to - 26. This is somewhat smaller and dimmer than what we see from Earth, although not noticeably so to the casual observer; the most immediate consequence is that solar panels would only generate about 40% as much electricity as they do at home. So we wait for the Sun to go down. Interestingly, the rovers observe the otherwise reddish Martian sky to take on a purple or bluish tinge near the setting Sun, essentially the reverse of the familiar situation on our home planet. But once the Sun is down, the night sky looks rather familiar, albeit with Deneb doing yeoman's work as the de facto North Star (it's currently within 10 degrees of the Martian north celestial pole). Mercury, Venus and the Earth are seen from the Martian vantage point as inferior planets. Mercury never gets more than about 19 degrees from the Sun (and even then only rarely so, only if greatest elongation occurs when Mercury is near aphelion and Mars near its perihelion), and is all but lost in the Sun's glare. Even Venus and the Earth are constrained to 32 and 46 degrees maximum separation from the Sun. Venus shines with a maximum magnitude of about -4, the Earth maxes out at about -3, and Mercury never gets brighter than around -1.5. All can be followed through a full range of phases, with Mercury's maximum apparent disc being 8", Venus's up to 26, and the Earth's, 46". The Earth, of course, would be an imposing naked-eye "double star," paired up with the +1 magnitude Moon, itself having an apparent diameter of up to nearly 12", with an easy naked-eye separation of 25'. The Earth and Moon would simultaneously go through the entire sequence of phases - the crescent Earth would be paired with the crescent Moon, increasing to approximately half-lit discs at greatest elongation, followed by a "full Earth" and "full Moon" as superior conjunction is approached, and so on. Interestingly, though, from Mars Mercury is observed to transit the Sun about once every three years, considerably more frequently than is observed from the Earth. Venus transits and Earth transits, as seen from Mars, are considerably rarer; there are about seven Venus transits per century (which is still more than the two per century visible from Earth), and about 1-2 Earth transits per century. The next Venus transit visible from Mars will be in 2030, and the next Earth transit will be in 2084. 2030 looks unlikely, but perhaps there will be astronomers on Mars to witness the 2084 Earth transit. The outer planets, once again, look rather similar. Jupiter, at opposition, would subtend an angle of about 53-57", compared to the familiar 48" maximum disc seen from Earth, and would shine about half a magnitude brighter, slightly more than -3.0. The remaining outer planets would appear essentially the same as from Earth. But the Martian skies would be dominated by its two Moons, Phobos and Deimos. Both would go through a full set of phases, just like our own Moon. But since both are irregularly shaped, the phases appear unusual, with misshapen crescents and gibbous blobs featuring long, irregular shadows. The inner moon, Phobos, shows an irregular disc subtending a maximum angle of about 12', slightly less than half the size of the Moon as seen from Earth, but still big enough to resolve its ovoid shape with the naked eye. Phobos is near enough to Mars that it is about 30% smaller when it is rising or setting versus a closest approach as it passes the zenith. (Think of an airplane - when down near the distant horizon it's farther away and appears smaller than when it passes overhead.) In fact, equatorially-orbiting Phobos is so close to Mars' surface that it is never visible at latitudes above about 70 degrees. Phobos' disc is smaller than the Sun's, so total solar eclipses never occur. Rather, when Phobos passes in front of the Sun, as it does almost every orbit for an observer someplace on Mars, its irregular potato-shaped silhouette causes a rather unusual "annular" eclipse, whose entirety from first to fourth contact lasts less than a minute! Several Phobos transits were observed by the Opportunity rover on the surface of Mars in 2004; Pho-bos blocks out about half the diameter of the Sun's disc. Since Phobos orbits Mars in 7.5 hours, faster even than Mars turns on its own axis, Phobos will, like a manmade satellite in low Earth orbit, rise in the west and set in the east, opposite the sense of all other objects in the sky, and complete one orbit of the sky in about 11 hours. Phobos' maximum brightness, at "full Phobos," is about magnitude -9, compared to -13 for the Earth's Moon. But "full Phobos" would rarely be seen because it passes through Mars' shadow on almost every orbit; there would be a "Phobos eclipse" once almost every 11-hour "Phobos month." Indeed, the "Phobos eclipse" is more closely analogous to the phenomenon of a satellite "blinking out" as it passes into the Earth's shadow than it is to what happens to our Moon. Deimos, the outer moon, is equally bizarre. Somewhat dimmer with its magnitude ranging from about 0 to - 5, its maximum angular size is approximately 2', small enough to appear stellar to the naked eye; its phases would be detected by the eye as variations in brightness. But Deimos and its irregular phases are easily seen in tripod-mounted binoculars or a telescope. In the considerably rarer, generally once-monthly, event that Deimos' small silhouette passes in front of the Sun as seen from somewhere on Mars' surface, the effect is rather similar to that of a Venus transit as seen from the Earth, except that the whole event transpires in a few minutes rather than a few hours. Just like the Phobos solar eclipses, a Deimos transit was first observed by the Opportunity rover in 2004. Deimos completes one orbit of Mars in just over 30 hours, rather close to Mars' rotation period, somewhat like a manmade geostationary satellite around the Earth. From the perspective of a Martian observer, Deimos appears to almost "hover" in position as the sky rotates about behind it. While the stars go around once every 24.6 hours, Deimos takes nearly six days to do the same. And in the time it takes Deimos to make one complete path around the sky, (from one "Deimos-rise" to the next) it goes through more than four complete phase cycles (from one "new Deimos" to the next). As we leave Mars for our next destination, we pause to land on Phobos and take a look back at the Red Planet. Mars, from our new vantage point, is a swollen red orb subtending an angle of nearly 45 degrees, comparable to the field of view of a Kellner or Orthoscopic eyepiece. It's not even strictly correct to speak of Mars as presenting a "disc" since we're still close enough that Mars is distorted much like a view through a fish- eye lens; only about 1/3 of Mars' surface is visible at any given time from Phobos, and vice versa. While it's difficult to determine accurate brightnesses for objects so large and distorted, the total light emitted from Mars at this distance amounts to a magnitude of about -20. This is still about a thousand times less light than is re- ceived from the 100-times smaller diameter disc of the Sun. Seen from Deimos, Mars is a more reasonable 17 degrees in diameter (about the size of an outstretched hand at arm's length), but since both Phobos and Deimos are in spin-orbit lock like the Earth's Moon, from any vantage point on either moon Mars will hover in the same position in the sky, aside from any wobbling due to librations. Next month we will travel to Jupiter and beyond, exploring how the planets look as seen from the outer solar system. GENERAL MEETING April 18, 2008 "Life in Space" Robert J. Cenker, Aerospace Systems Consultant What's it like to live and work in space? Robert J. Cenker found out firsthand when he flew on the Space Shuttle Columbia (STS 61-C) as the Pay-load Specialist for a six day mission from January 12th to 18th, 1986. In addition to overseeing the deployment of the RCA Satcom Ku-1 satellite, he performed a variety of physiological tests and operated an infrared imaging camera. Today, he works as a consultant with various firms on spacecraft design, assembly, flight operations and micro-gravity research. Mr. Cenker will share his experiences while showing slides taken dur-ing his flight as well as a short video. 8PM IN THE ROY SMITH THEATER EMAIL CONTACTS presi-dent@asterism.org President of AAI editor@asterism.org Editor of The Aster-ism Ray Shapp, Editor Deadline for submissions to each month's newsletter is the first Friday of that month. member-ship@asterism.org AAI Membership Chair trustees@asterism.org All three Trustees of AAI ray@asterism.org Ray Shapp for the website exec@asterism.org Executive Committee plus Trustees QOs@asterism.org All Qualified Observers Info@asterism.org AAI president, corresponding secretary, and computer services chair MEMBERSHIP DUES Regular Membership: $21 Sustaining Member-ship: $31 Sponsoring Member- ship: $46 Family Membership: $5 First Time Application Fee: $3 Sky & Telescope: $32.95 Astronomy subscription: $34 (Subscription renewals to S&T can be done directly. See "Membrship- Dues" on website for details.) AAI Dues can be paid in person to Membership Chair or Treasurer, or by mail to: AAI, PO Box 111, Garwood, NJ 07027-0111 DR. LEW'S SEMINARS See Dr. Lew Thomas for possible upcoming seminar topics. (Choice of topic at Dr. Lew's seminars is determined by par-ticipants' interest) DOME DUTY April 25 Team D May 2 Team E May 9 Team A May 16 Team B FRIDAYS AT SPERRY April 25, 2008 Ask The Astronomers Dr. Lew May 2, 2008 What's Up: A Down-to-Earth Sky Guide Kathie Vaccari May 9, 2008 Edmond Halley: More Than a Comet Hank Adams All schedules above were accurate at time of publication. Please check www.asterism.org for latest information (click on "Club Activities") Astronomy Day May 10 Noon to 5:30pm; 7:30 to 11pm See Special Notice page for events schedule May 2008 provides wonderful viewing opportunities for naked eyes, binoculars, and telescopes alike. First, something easy for everyone. Since before the beginning of winter, Saturn has been slowly moving backward, to the right, toward Regulus, the heart of Leo, the Lion. That little six degree gap between them that held the magnificent total lunar eclipse in February is down to just over two degrees as May begins, but on the 3rd, the journey is over. That's when the Ringed Planet resumes its direct motion to the left, not to get this close to Regulus again for almost thirty years. A low western horizon is needed to appreciate this year's best apparition of Mercury. The speedy little planet attains its maximum altitude above the western horizon around elongation from the Sun on the 14th, but don't wait that long. Mercury is only half illuminated by this time and is rapidly fading. The planet is half a magnitude brighter as the month begins and is only slightly lower. Break out the binoculars on the 6th when the 36-hour-old Moon is just five lunar diameters (2.5 degrees) to the upper right of Mercury. Once you find this pair, scan to the left to find Aldebaran, the eye of Taurus, the Bull, then continue directly to the left to see the horizontal belt of Orion, the Hunter. Both of these objects are usually very difficult to observe in the month of May. Because of the Full Moon, a telescope will probably be needed to see Mars pass just above Eta Cancri, a 5th magnitude star in Cancer, the Crab. At least we are in the perfect time zone. The planet and star will be less than a twentieth of a degree apart from 8:00 PM through 9:30 PM. Exactly four days later, telescope users will be able to see Mars pass so close to a star that the real time motion of the planet might be observable. Around 9:00 PM on the 23rd, the center of Mars passes only 16 arc seconds above the 7th magnitude star HD 73974. That's 1/225 of a degree, and only about three times the apparent diameter of the planet! Since Mars is moving 1.4 arc seconds every minute, its motion may be de-tectable over a single observing session. Between these last two events, Mars passes through The Beehive at the center of Cancer. This open star cluster, also known as M44 or The Praesepe (pray-SEE-pee), is a lovely binocular object even without the presence of the Red Planet. Finally, night owls will have to stay up until well after midnight to see Jupiter rising. Venus watchers will have to wait until August. Science Outreach and Update by Ken Kremer Cassini Flies through Erupting Geysers of Enceledus On March 12, the Cassini spacecraft tasted and sampled a surprisingly rich mixture of organic materials dur-ing an extremely close flyby just 30 miles above Saturn's Geyser Moon. Cassini flew directly into the plumes of water and a brew of simple and complex organic chemicals erupting through 95-mile long fractures at hot spots at the south polar region of the tiny moon Enceledus. "A completely unexpected surprise is that the chemistry of Enceladus, what's coming out from inside, re-sembles that of a comet," said Hunter Waite, principal investigator for the Cassini Ion and Neutral Mass Spec-trometer at the Southwest Research Institute in San Antonio. "To have primordial material coming out from inside a Saturn moon raises many questions on the formation of the Saturn system". "New heat map data also discovered that the temperatures at the fissures were warmer than expected, which could mean that liquid water exists not far beneath the surface of Enceladus. Therefore the moon has most of the essential ingredients believed required as precursors to life: water, heat and organic molecules. NASA Link to image and cool animation: http://www.nasa.gov/mission_pages/cassini/multimedia/pia10354.html STS-123 Mission: Space Shuttle Endeavour landed in darkness at 8:39 PM on March 26 after a tremen-dously successful record breaking 16-day mission to the International Space Station (ISS) to deliver and install the Canadian Detrxe robot and the Japanese manned Logistics Module. 15 minutes before the shuttle landing at the Kennedy Space Center, I observed the ISS and new European ATV cargo ship speedily passing over-head. It was the brightest and most spectacular ISS viewing that myself and other astro friends had ever seen. DAWN Asteroid Orbiter: All systems are "Go" at T-minus 1 year from the Mars gravity assist fly-by to pick up speed on the way to Asteroid Vesta. My review articles about Dawn and the Delta Rocket Launch Complex 17 have just appeared in the March & May 2008 issues of Spaceflight Magazine from the British Interplanetary Society (see links below). Learn more at my upcoming talk on April 26 at NorthEast Astronomy Forum (NEAF) (see dates and times further below). http://www.bis-spaceflight.com/sitesia.aspx/page/184/id/1649/l/en-us http://www.bis-spaceflight.com/sitesia.aspx/page/183/id/1678/l/en-us http://www.bis-spaceflight.com/sitesia.aspx/page/183/id/1715/l/en-us Science and Engineering Expo in Princeton, NJ: On March 19th, I participated with a 3-D Solar System Exploration display at the 5th annual Science and Engineering Expo which was attended by over 1,000 middle school students from central New Jersey. This science fair extravaganza is sponsored by Princeton University and it exposes children to the thrills of a wide range of research disciplines including Biology, Chemistry, Com-puters, Geology, Physics, Ecology, Engineering, Astronomy and more. The goal is to enlighten the students and interest them in careers in science and engineering. Please contact me for more info or science outreach presentations. My upcoming Astronomy talks include: Orchard Hill Elementary School: Montgomery Twp, NJ, April 14,16,28,29, 6:30 PM. "Twin Robots Exploring Mars in 3-D". May 5 & 8 at 6:30 PM Gloucester County College: Sewell, NJ, April 23, 8:30 PM. "Exploring Mars (and Asteroids), the Search for Life, and a Journey in 3-D". Heath Sciences Building, Room 500 Website: http://www.gccnj.edu/ & http://www.gccnj.edu/general_information/ken_kremer.cfm NorthEast Astronomy Forum (NEAF) at Rockland Community College: Suffern, NY, April 26 & 27. "Launching DAWN to Asteroids"+"Exploring Mars (3-D)". Sat Apr 26 at 2:30 PM & Sun Apr 27 at 1 PM Website: http://www.rocklandastronomy.com/neaf/NEAF_Schedule.html United Astronomy Clubs of New Jersey (UACNJ) at Jenny Jump Observatory/Park: Hope, NJ, Sat, Jun 28, 8 PM. "Twin Robots Exploring Mars (in 3-D)". Website: http://www.uacnj.org/ Dr. Ken Kremer Email: kremerken@yahoo.com NASA JPL Solar System Ambassador