Volume XIX No. 7 March 2008 Calculating Dark Matter Index of Binary Galaxies By Ed Carlos An AAI Research Committee Project I n May of 2007, I presented a talk titled, "Measuring Galaxy Mass Using SDSS SkyServer" in the Fridays At Sperry series for Amateur Astronomers, Inc. I demonstrated how to use the SkyServer website of the Sloan Digital Sky Survey (SDSS) in determining the luminosity mass and the velocity mass of galaxies. The premise was to use binary galaxies for de-termining the orbital velocities and total masses of the galaxy pairs. I have since adopted that presentation as the basis for one of the Research Committee's projects: "Calculating Dark Matter Index of Binary Galaxies". The goals of the project are to calculate the "Mass to Light" ratio of binary galaxies and to compare our results with the "Dark Matter Index" published by professional astronomers. Our project has multiple objectives in order to meet these goals. These ob-jectives are: " Learn about the Sloan Digital Sky Survey and the tools available on their SkyServer website " Learn how to mine the large amount of data avail-able on the SDSS SkyServer via the internet. " Define proper criteria for selecting binary galaxies " Calculate luminosity mass of galaxies " Calculate velocity mass of galaxies " Determine the mass to light ratio or Dark Matter Index " Publish findings I would encourage all AAI members to participate in this project. It is relatively easy to do. Just access the internet, use simple math, and have plenty of enthusi-asm for learning. So what is this Sloan Digital Sky Survey anyway? It is simply the largest effort to map the universe. The survey was undertaken by the Astrophysical Research Consortium which owns and operates the Apache Point Observatory, located in Sunspot, New Mexico. The APO houses the 2.5 meter SDSS telescope. So far, the SDSS has produced 40 terabytes of data. They imaged eight thousand square degrees of the sky and detected over 200 million objects. They collected spectral data for more than 675,000 galaxies, 90,000 quasars, and 185,000 stars. Even more impressive is that they have made all of this data easily available to the public using many of their tools. The tools vary from simple ones like the "Navigate Tool" to more advanced tools such as SQL Query. Each tool is easy to learn, and they provide plenty of tutorials and help menus. The SDSS website is at www.sdss.org. The SkyServer is at http://cas.sdss.org/dr6/en/. Follow the Help menu on the SkyServer site to learn how to use its tools, to find definitions of the data elements in its database, and for much more. Once you get familiar with the site and the available tools you can try out some of their interesting projects like the very simple and intuitive "Scavenger Hunt" (which is highly recommended for school children) or the more advanced projects such as the "Hubble Diagram". In the Hubble Diagram project you will learn about galaxy distances, their redshifts, and how they relate to each other. You will also create your own Hubble Dia-gram based on data that you will retrieve from their database. Understanding galaxy distances and redshifts and learning to use the Navigate Tool will be critical in our project. Our "Calculating Dark Matter Index of Binary Galaxies" project will require many data points in order to get satisfactory results. Cooperative participation among AAI members will allow us to validate our approach and our calculations by cross checking our selection criteria, formulas, and results. We begin by finding suitable galaxies using the Navigate Tool for simple searches, or the Query Tool for more advanced searches. Candidate galaxy pairs should be separated by a minimum of about 300,000 light years to a maximum of about 5 million light years. The "Famous Places" tool shows a selection of interacting galaxies, however, to make a more precise selection, we will need to find them using "Visual Tools". The Navigate Tool (see Figure 1) allows users to specify Right Ascension and Declination of the objects or the vicinity of the objects that we want to retrieve. It then provides a user-friendly navigation window to retrieve photometric and spectral data. This tool is sufficient for photometric values, but we need to use the "Query Tool" to get redshift values. That's because the "Query Tool" provides enough significant digits for use in our formulas. For example to select all galaxy objects within a redshift range of 0.02 to 0.019, we execute the Standard Query Language statement in the Query Tool as shown in Figure 2 below. The following table contains a sample result set of the query above. Notice that the values of z in the redshift column are very high. These will need to be scaled back before using them in any of our calculations. specObjID z modelMag_r RA DEC '211612124965765120 1928.64001 18.09078 0.72963331 14.36000905 '109434742599843840 1938.66003 17.126781 2.31540189 0.81259077 '109998151309459456 1906.33997 17.28809 5.00714814 0.65394921 '184027122854002688 1999.12 17.02256 5.69338232 -9.90956466 '184027122908528640 1997.93005 17.421446 5.95133203 -9.65272937 '110560641441333248 1954.54004 16.926638 7.68242045 -0.29956853 '110279120163700736 1913.44995 15.682716 7.71735774 0.52874649 '184308601874022400 1992.46997 14.179066 7.72403524 -9.20785945 '110279120335667200 1917.31995 15.707749 7.75249079 0.43574902 '110279118154629120 1946.23987 14.089925 7.80037989 -0.40734756 Once we have the candidate galaxy pairs, we can start filtering them using their right ascension, declination, photometric magnitude value, and their redshift values. These attributes will be used to calculate the distance between the two galaxies in a pair, and the distance from that pair to us. To account for the error between the galaxies in a pair introduced by projection onto a two-dimensional coordinate system, we can use the Pythagorean Theorem and the RA/DEC coordinates of the two galaxies. The pair of RA/DEC values will produce a hypotenuse that can be converted to light years. To obtain true distances, we must compensate for redshift. Applying this redshift data to a known constant, i.e. the age of the universe, we can estimate the distance of the galaxies from us. From those distances we can further refine the distances between the two galaxies in a pair by using the Pythagorean Theorem again. Knowing the adjusted distances, we can calculate the Luminosity Mass of the galaxies by using the photometric value of the galaxies found by the tool, and then converting it to the flux value, and dividing it by the square of the distance: Lg / Ls = (fg / fs )* (dg / ds)2. In other words, the luminosity produced by the galaxies is spread out onto an area. Using a known reference, i.e. the Sun, the luminosity of each galaxy can be calculated in units of Suns. Calculating the velocity mass requires the proper value of separation distance of the two galaxies. Employing the process described above, we can simply calculate the mass using the velocity of the two galaxies as they orbit a common center of mass using Newton's formula M = ()v)2R / G. Were v is the velocity based on the redshift of the pair, R is the distance between the pair, and G is the gravitational constant. Similar to the luminosity mass, we will convert this to units of Suns: Mgal / Msun = (vgal / vsun)2 * (Rgal / dsun). After both Luminosity Mass and Velocity Mass are calculated, the Dark Matter Index is simply the ratio of Velocity Mass over Luminosity Mass otherwise known as Mass to Light ratio or M/L. Applying this technique to NGC799 and NGC800, I obtained the results shown in the following table. Galaxy Mag-nitude Flux (rela-tive to the Sun) RedShift Distance from Us* Distance Between Pair* Luminosity Mass** Velocity Mass** M/L NGC799 13.01 1.30617e-16 0.019709 260 3 34 586 11.26 NGC7800 13.84 6.08135e- 17 0.019885 263 same 16 same same *(Million Light Years) **(Billion Suns) As you can see the formulas that we will use for our project are very basic, and the tools are very intuitive, not to mention fun to use. So, it is more difficult to find an excuse not to participate than it is to join with us. If any of these concepts seem too complex, I am always available to walk any AAI member through the process. As a matter of fact, I will be scheduling a few training sessions on the SDSS SkyServer tools and, of course, I will have regular Research Committee meetings to discuss the project itself. So, I encourage you to speak to me during our meetings or to email me at edcarlosm51@gmail.com. To-gether we can bring this project to fruition. The Mayan Eclipse Prediction Technique By Dr. Lew Thomas and Anita Glick To me, the ancient Mayan civilization of Mesoamerica was a remarkable culture. Beginning in the BCs and extending into the Greek and Roman classic eras, the Mayans had developed a number system superior to that of their European counterparts. While the Romans struggled with their cumbersome counting system, the Mayans had, for hundreds of years, developed the concept of zero. Their numbers consisted of only three symbols. A dot was a one. Five was represented by a horizontal line and their zero was an empty clam shell. They wrote their numbers in vertical tier and their system was based on units of 20 (why not, if you ran about in bare feet you would probably do likewise). Today astronomers use the Julian Day Numbers which are a count of days since noon on January 1, 4713 BC. (Ed note: See Dr. Lew's article on page 10 in the February 2008 issue of this newsletter for a discussion of Julian Day Numbers.) The Mayans had the "Long Count" which was also a count of days since some far distant event, probably mystical. Mayans produced a Venus table of great accuracy to indicate when Venus would first appear in the evening and then in the morning before sunrise. Their greatest achievement was the prediction of solar eclipses. When such an event had been viewed they could forecast to the day when the next should be expected to occur. It might not occur at that predicted time, but it could not occur on any other day near the time predicted! Let's examine their method. A solar eclipse must occur somewhere on the Earth each time the Sun arrives at a lunar node which is the place where the lunar orbit intersects the ecliptic. This is because the Sun's motion is slow enough that the Moon surely will pass through a node while the Sun is close enough to be eclipsed. Therefore, a solar eclipse must occur at least every half eclipse year1 of 173.31 days on the average. Of course, a solar eclipse demands a new Moon which occurs each synodic month of 29.5306 days. We start by asking how many days should elapse between each successive solar eclipse. At first you may think that 173 days would be a good approximation since it is close to half an eclipse year (173.31 days). However, we note that this figure divided by a synodic month yields the non-integer value of 5.85. Using 174 would yield 5.87. An eclipse table based upon these figures would quickly creep away from the time of new Moon. What approximation did the Maya use? Examining whole numbers in the vicinity of 173.31, we see that 177 and 178 result in the least departure from an integer when divided by the synodic month. This is shown in Table 1. Table 1: Approximating Integers Near 173.31 Days Approximating Integer Result When Divided By Synodic Month Departure From An Integer 171 172 173 174 175 176 177 178 179 180 5.79 5.82 5.86 5.89 5.93 5.96 5.97 6.03 6.07 6.10 0.21 0.18 0.14 0.11 0.08 0.04 0.03 0.03 0.07 0.10 It is also possible for the Moon to eclipse the Sun just one synodic month short of an eclipse year. This oc-curs when, in the first instance, the Sun is west of a node, but eclipsable, and then half an eclipse year later, minus one synodic month later, the Sun is within 0.5 degree of the minor limit and again eclipsable. Subtracting one synodic month from 173.31 yields 143.779 days. Table 2 shows that the best integer value to represent this span is 148 days. Table 2: Approximating Integers Near 143.779 Days Approximating Integer Result When Divided By Synodic Month Departure From An Integer 142 143 144 145 146 147 148 149 4.80 4.84 4.88 4.91 4.94 4.98 5.01 5.05 0.19 0.16 0.12 0.09 0.06 0.02 0.01 0.05 It is remarkable, that the ancient Mayans of Mesoamerica chose these very numbers -- 177, 178, and 148 -- with which to construct their solar eclipse tables. When an eclipse occurred, they predicted that another eclipse 177, 178, or 148 days later would be possible. These spans are the very best choices possible and, more sur-prisingly, this was accomplished before the Greek and Roman empires flourished! Generally, 177 or 178 days occur between successive solar eclipses and for this interval to be valid, a lunar eclipse must occur between successive solar eclipses. When the generally intervening lunar eclipse is not present, the interval between successive solar eclipses is reduced to 148 days. In the Dresden Codex of the Mayans, this 148 day interval is marked by placing a picture immediately after its notation. Stewart's Skybox by Stewart Meyers C oming up with a topic for this month's column was a challenge. I was considering discussing the problems of astronomical webcasts since it looked like the lunar eclipse on February 20th was going to get clouded out for AAI members. Fortunately, that was not the case. But, the eclipse and two other events helped in picking a topic. First was Bonnie Witzgall's fine presentation that evening titled, "A Tale of Two Moons" which compared Jules Verne's vision of a mission to the Moon and the actual Apollo program. Especially amazing was how close Verne came when he computed the cost of the mission. When adjusted for inflation, he got within the correct order of magnitude and was only off by about two billion dollars. The other event was the passing of veteran actor Barry Morse. While most people remember him for his portrayal of Lt. Philip Girard, the persistent detective who pursued Richard Kimble on the original "The Fugitive" TV series (probably what he would have preferred to be remembered for), Barry Morse did have a connection with the Moon that he probably regretted. Back in 1976, he portrayed the intelligent, but low key Professor Victor Bergman on Gerry Anderson's special effects laden but quality-challenged science fiction series "Space: 1999". With these fictional examples of lunar activities, one good (Verne's books) and one poor ("Space: 1999"), it might be a good idea to take a look at some of the real issues involving the return of humans to the Moon as the United States, Russia, and China are proposing. The Saga Begins (Again) Most sane people who know anything about space history know that Apollo 11 landed on the Moon in 1969 and that the last time humans went to the Moon was the Apollo 17 mission in 1972. After that, interest in the Moon faded away. Except for the Soviet Lunokhod rovers in the early 1970's, the Clementine mission in 1994, Lunar Prospector in 1998, and the European Space Agency (ESA) SMART-1 mission in 2003, the Moon was pretty much left alone. However, that changed in January of 2004. Likely out of concern about the steady pace of the Chinese space program, President Bush proposed what has been billed as the Vision for Space Exploration (VSE). This plan calls for, among other things, sending humans back to the Moon. After some debate of the design of the rockets and the required vehicles, it was decided to take a bit of a leap backward and use what amounts to warmed-over Apollo-era designs with rela-tively minor improvements. For example, the Crew Exploration Vehicle (CEV) is essentially an enlarged ver-sion of the Apollo command module. The service module is somewhat similar to the Apollo version but will use solar panels to generate electricity instead of fuel cells. Some of these features can be seen above in the NASA artist's conception of the CEV. And the engines in the Ares heavy lift rocket are almost the same as those of the Saturn V of the Apollo mission. However, this article is not about the technology of the VSE and its relative lack of innovation, though this might be covered in a future article. Other nations are trying for the Moon as well. China has launched Change'e 1, which now orbits the Moon and is mapping its surface. The Chinese also plan to send people by the year 2020. India is planning to launch a lunar orbiter called Chandrayaan 1 later this year, possibly this summer. Also, the Russians have announced that they are working on plans to send humans to the Moon by the 2020s. While they are not planning any manned missions, the Japanese have sent the Kaguya probe, which is taking amazing images of the Moon such as the one seen here. Kaguya also transmits high-definition video. All this, along with proposed NASA lunar probes, shows a resurgence of interest in the Moon. If the VSE manages to survive the current recession and upcoming change of administrations in Washington or one of the other spacefaring nations succeeds in their lunar plans, there are certain things that have to be considered when setting up a human presence on the Moon. In fact, there are three major issues that have to be addressed or at least analyzed if any lunar base is to succeed. A Matter of Gravity One fact that was known about the Moon even before the space age was that the pull of gravity at the lunar surface was only one sixth that of the Earth's. H.G. Wells made use of this in his book, "First Men in the Moon". While the Apollo astronauts seemed to have little difficulty in moving around while on the lunar surface, the effect of living for an extended period in somewhat reduced gravity is not well known. The effects of micrograv-ity on humans who are in space for months are well documented and include loss of bone mass, muscle atro-phy, and a weakening of the immune system. While it is not very likely that the reduced lunar gravity would be as bad, some have suggested that the effects would be scaled down versions of what happens in microgravity. A number of science fiction stories have been written where people who spend long periods of time in reduced gravity (like on the Moon or on Mars) are unable to return to Earth because of the effects which would leave them unable to function. But it is possible that even lunar gravity would be sufficient to avoid those consequences. I suspect that this will likely be the case. Dust in No Wind One of the benefits of setting lunar bases is that metals useful for space travel can be mined, saving the ex-pense of building and sending up spacecraft from Earth. Contrary to what was shown on the episode "Demons" of "Star Trek: Enterprise" which depicted lunar mining as similar to mining on Earth, the process would be much different. As discussed in the September 2006 column as well as what was shown in the recent AAI display about the minerals of the Moon, there are only a small number of minerals on the Moon, and most of them are metallic oxides, mainly oxides of aluminum, titanium, and chromium. Many of these are found in the regolith, a techni-cal term for the layer of dust that is just lunar rock that has been ground up by billions of years of micrometeor-ite impacts as well as by larger impacts. Most proposals for lunar mining call for scooping up the regolith and dumping it into a processing system that would separate the oxygen (which would be used for life support and rocket oxidizer) from the metallic oxides, leaving the metal. Unfortunately, lunar dust has a dark side, a very serious dark side. When examined under microscopes, the dust was found to consist of very jagged particles and tiny bits of glass. This should not have been surprising since there has never been any substantial atmosphere or liquid water on the Moon. As a result, there is no erosional process that can soften the edges of the particles. The bits of glass form when micrometeorites strike the surface and melt tiny quantities of regolith, which quickly solidifies into glass. These particles can be extremely abrasive. In November of 1969, the Apollo 12 mission landed within 600 feet of the Surveyor 3 lander, which landed in April of 1967. During the 31 months Surveyor 3 had sat on the lunar surface, the exposure to the varying temperatures of lunar day and night and the intense sunlight plus the other aspects of the lunar environment had darkened the paint on the probe. One of the objectives of Apollo 12 was to examine the probe and return parts of it to Earth for analysis. It was found that the side of Surveyor that faced the lunar module was no longer darkened. In a recent study of the Surveyor 3 camera, which was sent back to Earth, Philip Metzger of NASA's Kennedy Spaceflight Center discovered that the part of the camera that was facing the lunar lander was covered in microscopic pits and cracks, as if it was hit with a sandblaster. That was because the exhaust gases from the lunar module descent stage kicked up lunar dust and sent it flying far enough and fast enough to scour part of the lander. Further analysis of footage taken by Apollo astro-nauts during lunar landings as well as computer modeling confirmed this, and found that some of the smaller dust particles could travel considerable distance from the landing site. If there are regular landings and take-offs at a lunar base, this could be a serious problem. One suggested solution would be to create an artificial hill or berm between the landing area and the base. It turns out that the crew of Apollo 17 narrowly avoided a serious dust-related problem. The abrasive dust got into the shoulder joints of the spacesuits and as well as the glove locking rings. Fortunately, the damage was not serious or the results might have been disastrous. Besides the known detrimental effects of these par-ticles on machinery, it is unknown what effect exposure to lunar dust would have on the crew over the long term if it gets tracked into a lunar base. Also on Apollo 17, Harrison Schmitt developed a respiratory ailment which was thought to be due to inhaled lunar dust. Controlling lunar dust is easier said than done. It clings to just about everything. Part of this is due to the jagged shapes of the particles, but there is another factor involved. The total lack of any real atmosphere or significant magnetic field on the Moon means that dust particles pick up an electric charge from ionization while exposed to solar x-ray emission. Dust in the shaded areas do not. This electrical difference between shaded and exposed particles creates an electric potential, which can levitate very small dust particles about a foot or so off the ground. Images taken from Surveyors 5 through 7 shortly after sunset show a glow along the horizon near the sunset point. It was discovered that this glow was the result of levitated dust particles on the horizon. Adding support to this view was that the glows faded away in less than three hours. This property of lunar dust will no doubt complicate efforts to reduce its harmful effects. Bricks and Fields Since the Moon has no real magnetic field, though some very weak localized fields have been detected, the lunar surface is subject to the full effects of cosmic radiation as well as to bombardment by charged parti-cles from the Sun. This can create some curious phenomena as described above, and it allows the lunar re-golith to store a history of the solar wind. It can have negative consequences on people working at a lunar base as well. This is not hypothetical. Astronauts and cosmonauts have reported seeing sudden flashes of light, even while in their spacecraft. These flashes were caused by cosmic ray particles zipping through the eyeball. The vitreous humor acts like water in a particle detector and the eye registers the resulting flash. And, according to recent medical studies, this causes space travelers to have a higher risk of developing cataracts. It is also likely that other kinds of disorders caused by radiation would be more prevalent among space travelers as well. It could be worse. Back in August of 1972, there was an enormous solar flare. Fortunately, it happened during the period between the Apollo 16 and Apollo 17 missions. If the flare had happened while the astronauts were aloft, they would, at the very least, have returned with acute radiation sickness. The obvious answer to protecting a base crew from radiation is to have some sort of shielding at the base. But this is a bit more complicated than it seems. On Earth, if you want to shield someone or something from radiation, you would use lead. That is why people who are getting x-rays wear a heavy apron (contains lead), and the x-ray technician stands behind a thick metal wall. However, that approach would not be very effective in space. First, lead or any other metal suitable for radiation shielding is very heavy and therefore extremely costly to launch from Earth. Next, when cosmic ray particles strike an atom, they can create secondary parti- cles that are sometimes even worse than the original particle. Shielding made of heavy metal would suffer from this problem. Another way to shield against radiation is to go underground. On Earth, neutrino detectors are usually placed at the bottom of mines since the overlying rock keeps cosmic rays from reaching the apparatus causing false detections. This same idea has been proposed for lunar habitats. Excavating an area of lunar surface sufficient for a habitat will not be cheap. And such large-scale projects on the surface would undoubtedly run into problems caused by lunar dust. An alternative would be to find a crevice or a narrow rille in the lunar surface and to put the base at the bot-tom. This would shield the sides of the structures while leaving only the upper parts exposed. Some planners have proposed piling lunar regolith over the base structures, except for the parts that need to be exposed to the surface. Given the properties of lunar dust, it might not be such a great idea to cover the base with what amounts to abrasive grit. Another version of the idea calls for the lunar regolith to be put into containers (lunar sandbags?) which would then be piled around the structures. Then there are those who ad-vocate putting the regolith into molds, heating it until it melts to form bricks. These bricks could then be stacked around the base structures. Actually lunar bricks are not as farfetched as you might think. Experiments have been done with lunar soil simulants as well as with tiny quantities of actual lunar material. Lunar regolith is not difficult to melt, especially when one uses microwave heating. Then there is another proposal for radiation shielding on the Moon that was inspired by an Earthly example. On Earth, we are protected from cosmic radiation by the Earth's magnetic field. Charles Buhler of ASRC Aerospace has come up with a plan that calls for creating an electromagnetic field by using conducting spheres mounted on masts surrounding the lunar base. In fact, the artist concept is somewhat reminiscent of the infamous "Bergman shield" from "Space: 1999". These spheres would then be charged so as to generate an electromagnetic field that can repel cosmic ray particles as well as particles from the Sun. However, this concept may have a problem given the electrostatic properties of lunar dust. The Future You might get the impression that I am pessimistic about lunar bases. I am not, though I do question the chances of the VSE to succeed. Yes, there are some serious obstacles to lunar settlement, but they are proba-bly not insurmountable. These problems can be solved, though it might take quite a bit of time. But the benefits of solving them are immense. Such knowledge would allow humanity to set up settlement on not only the Moon, but Mars as well. There are benefits to setting up bases on the Moon besides exploration. In his book, "The Survival Impera-tive", William E. Burrows cites the advice given by almost every Information Technology professional and prac-ticed by most companies: Back up your important information and keep the backups at a separate location. In this case, Burrows refers to not only computer data but our cultural information as well. A lunar base could function to maintain a backup of the collected knowledge and culture of humanity. In event of a catastrophe on Earth, civilization could be jumpstarted using the data from the lunar archive. Also, the Moon would make a better spaceport than Earth. Lunar metals could be used to construct space-craft and the reduced gravity and no atmosphere would make launching said space vehicles much easier. Then there are the huge savings of not having to send spacecraft or materials needed for space up from Earth. Finally, the Moon would probably be a better place for high technology society than the Earth. This is proven regularly on the news. Almost weekly, the news media has reports of floods, tornadoes, hurricanes, tsunamis, earthquakes, etc., causing damage to cities and towns. The Moon with its lack of atmosphere and its very weak seismic activity would not have these problems. Aside from the dust problem, cosmic radiation, and the occasional solar flare, the lunar environment is rather static. So it is quite possible that there will be a human presence on the Moon in the future, maybe even in a few decades. Only time will tell. About The Recent Total Lunar Eclipse By Dr. Lew Thomas On February 20, 2008, many of us witnessed a total lunar eclipse. This occurs when the Moon passes totally within the dark or unbral shadow of the Earth. As you probably know, the Earth casts two shadows because the Sun is an extended body. The unbral shadow is shaped like a cone whose base begins at the Earth and whose tip extends beyond the orbit of the Moon. Within this shadow, the only solar light is that which is refracted by the Earth's atmosphere. In passing through the atmosphere, the sunlight is shifted toward the red end of the spec-trum. Indeed, the light may be so attenuated that the umbral shadow can become quite dark. The umbra colors can range from bright red, to brick red, to slate gray. It all depends upon the transparency of the atmosphere. Now, the Sun and Moon present approximately the same sized disk in the sky, because the larger physical size of the Sun is reduced angularly by its greater distance. If the Moon revolved around the Earth in an orbital plane positioned exactly in the ecliptic, we would have a solar and lunar eclipse each synodic month (29.5306 days). However, the lunar orbit is inclined 5.15 degrees to the ecliptic, causing the Moon to pass slightly above or below the half-degree solar disk most of the time. Again, because of the lunar orbit tilt, often the Moon will avoid the Earth's shadow during full Moon. The lunar orbit intersects the ecliptic plane at two points: (1) at the ascending node which is the intersection at which the Moon moves from south of the ecliptic to north of it; and (2), at the descending node where the Moon moves from north to south (about 180 degrees around the ecliptic). At these two nodes, solar and lunar eclipses can take place. Since the Sun, in its apparent yearly motion around the Earth, passes through these nodes about twice a year, solar and lunar eclipses occur at about that frequency. The least possible number of eclipses in a year is two, both of the Sun, while the maximum is 7: 5 of the Sun and 2 of the Moon, or 4 solar and 3 lunar. Usually, only 4 eclipses occur during a year. The region around each node where eclipses can take place is defined by the ecliptic limits. This states how far either the Sun (for a solar eclipse) or Moon (for a lunar eclipse) may be from the node and still produce an eclipse. These limits have both maximum and minimum values due to the eccentricity of the lunar and Earth orbits. For the Sun, the maximum values occur when the Earth is at perihelion (making the solar angular diameter largest) and the Moon is at perigee (making it largest angularly). The minimum solar ecliptic limits occur with the Earth at aphelion and the Moon at apogee. The major solar ecliptic limit is 18° 31' and the minor limit is 15° 21'. The Sun's apparent speed is such that it cannot pass through even the minor limit without having the Moon pass in front of it to produce a solar eclipse. At least one solar eclipse must therefore occur at each node or two per year. There are also lunar ecliptic limits. As you might expect their maximum value occurs with the Earth at perihe-lion (largest shadow) and the Moon at perigee (largest Moon). The minimum value is with the Earth at aphelion and the Moon at apogee. The major lunar ecliptic limit is 12° 15' and the minor is 9° 30'. Since the lunar limits are smaller than the solar ones, it is possible for the Moon to cross a node without encountering the Earth's shadow. Therefore, a year can go by without a lunar eclipse. That will happen in 2009. Lunar nodal regression also affects eclipses, but this effect is more evident for solar eclipses which present a small lunar shadow on the Earth. It has little effect on lunar eclipses which can be viewed by everyone on the Earth's hemisphere facing the Moon. Now For The Fun Of Recording Our Observations Most of us have viewed many total lunar eclipses and have noticed how they vary in brightness. The light penetrating the Earth's shadow (umbra) is, of course, sunlight which has been refracted into the shadow. This refracted light has traveled through the atmosphere of Earth whose clarity varies. Sometimes the eclipsed Moon is brick red, sometimes bright red, and sometimes you can't see it at all. The variations as we know, are due to varying amounts of water in the form of clouds, mist, and rain or snow, and to solid particles such as dust and volcanic ash. A volcanic eruption will spew thousands of tons of ash into the atmosphere which can persist for several years. Lunar eclipses following great volcanic eruptions are usually very dark. It has also been suggested that eclipses following hydrogen bomb explosions in the atmosphere (now outlawed) have decreased the brightness of refracted light. Those of you who have recently viewed this lunar eclipse might try to quantify your impressions. French as-tronomer A. Danjon proposed a scale to meter lunar eclipse brightness and color as shown in the following ta-ble. The following quote is from Fred Espenak ( http://sunearth.gsfc.nasa.gov/eclipse/OH/Danjon.html ): The assignment of an 'L' value to lunar eclipses is best done with the naked eye, binoculars or a small telescope near the time of mid- totality. It's also useful to examine the Moon's appearance just after the beginning and before the end of total-ity. The Moon is then near the edge of the shadow and provides an opportunity to assign an 'L' value to the outer umbra. In making any evaluations, you should record both the instrumentation and the time. Also note any variations in color and brightness in different parts of the umbra, as well as the apparent sharpness of the shadow's edge. Pay attention to the visi-bility of lunar features within the umbra. Notes and sketches made during the eclipse are invaluable in recalling details, events and impressions. Observers are encouraged to make Danjon brightness estimates and to report them to Sky and Telescope and to Dr. Richard Keen (richard.keen@colorado.edu). If you do follow Mr. Espenak's advice, please send a copy of your email to us at info@asterism.org. A Report On Near Earth Objects By Dr. Lew Thomas So called Near Earth Objects (NEOs) are asteroids or comets whose orbits cross that of the Earth. Hun-dreds of these have been tracked, and we have their orbits established to various degrees of accuracy. There are three which have recently become important; two of which pass close to Earth and the other which will have a close fly-by or a collision with Mars. The first NEO under consideration was called Toutatis. It passed close to Earth on September 29, 2004. This was a rather large NEO being an asteroid measuring 2.9 miles long and 1.5 miles wide. This one was large enough to produce global devastation if it had impacted Earth. Fortunately its orbit was well refined by NASA observers and others for over a decade. Its orbit was known to a precision of about its size. So on Sep-tember 29, Toutatis was predicted to miss Earth by a million miles and it did just that! (Continued next page) GENERAL MEETING March 14, 2008 "Plasma Propulsion and the Exploration of Space" - Prof. Edgar Choueiri, Princeton Univer-sity Professor Edgar Choueiri highlights next generation rocket technology that is crucial to enabling advanced missions to explore deep space. A brief history of rocketry will explain why the chemical rockets cur-rently used to send humans to the Moon are not feasible for ambitious deep space exploration. He will describe the basic physics of more advanced spacecraft propulsion concepts, such as nuclear and plasma propulsion, and show how the plasma rockets that have been successfully used on several recent small spacecraft are being evolved for the more ambitious missions that will define the next age of space exploration, such as a Jupiter moon tour, a Pluto or a Neptune orbiter, and sample return missions to Mercury, Titan, Europa, comets, asteroids and Kuiper Belt objects. Professor Choueiri leads a large team of researchers at Princeton University and at various NASA centers to develop new plasma rocket technology. His experiments have flown on the Space Shuttle and Russian scientific spacecraft. Professor Edgar Choueiri is Director of the Engineering Physics Program at Princeton University as well as Princeton's Electric Propulsion and Plasma Dynamics Laboratory where he works on a new generation of rockets for spacecraft. See photos and description of special tour of Prof. Choueiri's lab beginning on page 19. 8PM IN THE MAIN LECTURE HALL Note: This meeting is on the second Friday of March because Union County College is closed on our usual meeting night, the third Friday of the month. Near Earth Objects (continued from previous page) Toutatis has an orbital period of about 4 years, so it will be around again. Fortunately, the Earth will be in a different position so such a near approach will not recur. However, orbits of asteroids are affected by the gravi-tational pull of nearby planets making it impossible to predict positions thousands of years into the future. So maybe, just maybe, this asteroid may revisit us and come even closer. The next NEO of recent interest is Apophis, originally called 2004 MN4. It is expected that this asteroid, which is substantially smaller than Toutatis, will have a very close approach to Earth in 2029 but no impact is anticipated This forecast is the result of orbit refinements based upon observations in December of 2004 and January, 2005 and radar observations from Arecibo at the end of January 2005. The orbits of NEOs which are classified as Virtual Impactors are constantly being refined using current ob-servational data to remove as many as possible from this list. The third NEO of current interest is asteroid 2007 WD5 which had been predicted to impact Mars on January 30th of this year. In early January, the impact probability was increased from 1.3% to 3.9% which is about 1 in 25 odds. Pre-discovery observations of this asteroid taken on November 8, 2007 resulted in orbit refinement yielding the above percentages. The uncertainty region near the Martian encounter is an ellipsoid extending over 400.000 km in length but only 600 km wide. This uncertainty region includes Mars itself so that a collision was still considered possible during the weeks prior to January 30th. Additional observations did shrink this uncertainty region, and impact was ruled out. According to Steven Chesley of JPL's Near Earth Object pro-gram, WD5 probably missed Mars by 6.5 Mars radii as reported by The Planetary Society's blog at http://www.planetary.org/blog/article/00001316/. This asteroid's orbit extends from just outside Earth's orbit to the outer reaches of the asteroid belt. This orbit was definitely perturbed by its close encounter with Mars, and it is now lost. 2007 WD5, however, is now very unlikely to pose a threat to the Earth. 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 March 14 Team C March 21 Team D March 28 Team E April 4 Team A April 11 Team B FRIDAYS AT SPERRY March 21, 2008 The MESSENGER Mission to Mer-cury Al Witzgall March 28, 2008 Ask The Astronomers Dr. Lew April 4, 2008 What's Up: A Down-to-Earth Sky Guide Kathie Vaccari April 11, 2008 Retro Rockets! A Space Race in Art Featuring the Imaginative Paintings of Chesley Bonestell Al Witzgall All schedules above were accurate at time of publication. Please check www.asterism.org for latest information (click on "Club Activities") April 2008 finds the planets widely spaced across the sky from dusk to dawn. Mars begins each evening high in the west as it races through Gemini. Its conjunction with Pollux on the 26th provides an interesting comparison. The orange planet is less than five degrees below the yellow giant star and calculated to be, at magnitude 1.2, exactly the same brightness. Will the steady light from the planet contrast to the twinkling light of the star? Saturn begins each evening equally high in the south as it continues its long, slow retrograde march toward Regulus that started in mid-December. The six degree gap that held the beautiful lunar eclipse in February is down to three degrees as April begins and two degrees just before the Ringed Planet resumes its leftward motion on May 3rd. At ten de-grees, the rings are near their maximum tilt of the year, not to be attained again until December 2009. Jupiter rises just as Mars sets around 3 AM. The Giant Planet will be the brightest point of light in the sky for the next four months. Jupiter crosses the ecliptic, the plane of the Earth's orbit, this month as it does just once every six years. For most folks, Venus has been an unnoticed morning object since last August. Well, from now until this August nobody at all will be able to see it! We do get one last chance to say good-by. On the 4th, look for the very thin crescent Moon just before sunrise. For a few minutes, the Brilliant Planet hangs about five degrees to its lower left. Then it's gone in the glare of the Sun until midsummer. Although Mercury passes beyond the Sun on the 16th, the last week of April begins its best evening showing of the year. At magnitude -1.4, the Speedy Planet starts out almost as bright as Sirius. Guide-posts are hard to find, but Betelgeuse-Aldebaran-Mercury make a long, equally spaced straight line from west to westnorthwest an hour after sunset. The Moon finds good company this month. On the 8th use binoculars to look for the Pleiades just above a thin crescent Moon. The northernmost members of the star cluster are actually occulted by the earthshine-lit part of the Moon. Other lovely grouping are listed in the calendar. Science Outreach and Update by Ken Kremer Mill Lake Elementary School: Monroe Twp, NJ, Feb 13. Well over 250 second grade students and their families attended this annual astronomy night extravaganza. It was tons of fun and excitement for all which included 4 presentations by myself on "Twin Rovers Exploring Mars in 3-D" and an armada of AAI Telescopes for demonstration viewing which was indoors on account of the rainy weather. The school teachers and prin-cipal Lynn Barberi set up about a dozen astronomy activity stations including a Starlab, Constellation Detec-tive, Name that Planet, Toilet Paper Solar System, Make Your Own Star Finder, Clay models of the Planets to scale, Space Stations and Telescopes. And they feasted on the ever popular Milky Way snack bars, Oreo Orbit cookies, Pluto pretzels and astronaut space drinks and food. . Photos: Ken Kremer These notes and pictures are posted on the Mill Lake school homepage for Astronomy Night on 13 Feb 2007 A great big "Thank You" goes out to all the astronomers who graciously volunteered their time and their own tele-scopes and binoculars for all to use. Unfortunately, the weather did not cooperate so we were not able to see views of the night sky. However, all were treated to learn about and look through the equipment in the gym. Dr. Ken Kremer, NASA JPL Solar System Ambassador, presented "Twin Robots Exploring Mars in 3-D". Thanks, Dr. Kremer, for taking us along with you to Mars. What a different planet it is! Is there water on Mars? The robots search for just that. What amazing pictures they have sent back to Earth too! Mill Lake staff Photos from Ken's Solar System Exploration Display Read more about Astronomy Night at the Mill Lake Elementary School and see lots more pictures here: http://monroenj.schoolwires.com/8602011112104530/blank/browse.asp?A =383&BMDRN=2000&BCOB=0&C=55336 Total Lunar Eclipse at the Franklin Institute with the Rittenhouse Astronomical Society (RAS): Philadel-phia, PA, Wed, Feb 20, 8 PM. Website: http://www.rittenhouseastronomicalsociety.org In spite of the gloomy weather forecast, a giant and enthusiastic crowd of over 400 people attended the mag-nificent and rare 20 Feb 2008 Total Lunar Eclipse event in the heart of Philadelphia jointly sponsored by The Franklin Institute and the Rittenhouse Astronomical Society. The festivities included roof-top viewing, astron-omy displays and my interactive multimedia presentations titled "Lunar, Solar and Martian Eclipses". Prior to the start of totality at 10:01 PM, about 100 folks came to 2 presentations to learn about the many different types of beautiful eclipses of our solar system illustrated at Earth, Mars, Saturn, manned space stations, ro-botic spacecraft and more ! The gracious crowd asked numerous excellent questions. In response, the weather gods cleared the skies of the evening snow showers and parted the heavens of clouds in the nick of time to reveal the eclipse by about 9 PM. Thereafter, hordes of kids and adults flocked to the roof-top Bloom Observatory for naked eye and telescopic viewing of the partial and then totally eclipsed and eerie copper col-ored moon, flanked by Saturn and Regulus. RAS members and myself helped enlighten all to this awesome astronomical event of nature. Not for another millennium, will the triangular nature of this eclipse be repeated! AAI member Ray Shapp has helped me with previous astronomy outreach events here. 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 Dawn review article has just appeared in the March 2008 issue of Spaceflight Magazine from the British Interplanetary Society (see links below). Learn more at my upcoming talk on April 2 at the Raritan Valley Community College Planetarium (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 Please contact me for more info or science outreach presentations. My upcoming Astronomy talks include: WNTI 91.9 FM Public Radio Interview: Centenary College, NJ, Sun, Mar 23, 7:30 AM. "DAWN Asteroid Or-biter" and more is the topic of my Radio interview with Karl Hricko from the WNTI "CONTOURS" program. Website: http://www.wnti.org/Raritan Valley Community College Planetarium: Somerville, NJ, Wed, Apr 2, 7:30 PM. "Launching DAWN (and Phoenix): From Behind the Scenes at Kennedy Space Center Press Site". Website: http://www.raritanval.edu/planetarium Washington Crossing Nature Center: Titusville, NJ, April 12, 1 PM. "Mars, Saturn, Asteroids and Beyond' Orchard Hill Elementary School: Montgomery Twp, NJ, April 14,16,28,29, 6:30 PM. "Exploring Mars in 3-D" NorthEast Astronomy Forum (NEAF):Suffern, NY, April 26&27. "Launching DAWN" +"Exploring Mars in 3- D" 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 Electric Propulsion Lab Tour at Princeton University By Ken Kremer Princeton University Professor Edgar Choueiri is the speaker at the 14 March 2008 AAI General Meeting. His lecture is titled "Plasma Propulsion and the Exploration of Space" and he will introduce AAI members & friends to his group's research. Prof Choueiri is the Director and Chief Scientist of the Plasma Propulsion Lab located in the Department of Mechanical and Aerospace Engineering (MAE) lab, officially designated the Electric Pro-pulsion and Plasma Dynamics Laboratory (EPPDyL). I have collaborated on astronomy outreach with Prof Choueiri in the Princeton area and at his kind invitation I led a tour of his lab on 21 June 2007 (see pictures below). EPPDyL has been at the forefront of research in the physics and application of plasma thrusters for spacecraft propulsion for more than three decades and is currently involved in active space experiments. Lab Website: http://alfven.princeton.edu/index.htm Research activities encompass performance studies of plasma thrusters, basic research in plasma problems relevant to plasma acceleration and development of probe and optical diagnostics. The activities also include some non-propulsive topics in plasma dynamics like space plasma physics problems. Prof Choueiri warmly greeted our group of 8 enthusiastic amateur astronomers from the New Jersey area in-cluding myself and AAI members Ray Shapp and Steve Krisocki. The EPPDyL lab tour gave everyone on the tour a fabulous and rare behind the scene's view into the nuts and bolts of cutting edge research that can revo-lutionize our ability to explore the cosmos and unlock her deepest mysteries with futuristic scientific instrumen-tation. The laboratory facilities include an array of large vacuum chambers for operating pulsed and steady-state thrusters under realistic space conditions, specialized optical and probe diagnostics, a broad spectrum of high speed digital data acquisition instruments and computers. Prof Choueiri was quite generous in spending over 2 hours to show us all 4 of the fully operational vacuum facilities and described how they are used in experi-mental research (pictures below). The Large Dielectric Pulsed Propulsion (LDPP, left) and Steady-State Low-Power (SSLP, right) Facili-ties: The vacuum vessel for the LDPP facility is an 8 ft diameter, 25 ft long fiberglass tank with thirty-one opti-cal access ports. This tank currently holds the record for vacuum level achieved at EPPDyL at 2.5x10-6 torr and is maintained by a 48 inch diameter CVC diffusion pump with a pumping capacity of 95,000 l/s and is backed by a roots blower (3000 cfm) and two mechanical Stokes roughing pumps in parallel. This vessel is equipped with liquid Nitrogen cooled baffles (see the LN2 cylinder foreground), which are used to lower the level of con-taminates present in the vacuum. These baffles halt the migration of pump oil into the test section which has been shown to skew experimental performance data. Photo Credit: Ken Kremer A plasma thruster is an electric rocket that accelerates a plasma to velocities of tens of kilometers per second making it a propulsion option that is well suited for energetic deep-space missions as well as attitude control and orbit raising for near-Earth spacecraft. By contrast, the best of today's chemical thrusters give exhaust velocities an order of magnitude lower (4-5 km/s). High exhaust velocities will be required to efficiently trans-port large masses of equipment, cargo and some day even people for ambitious missions to Mars and beyond in Deep Space and using as little propellant as possible to do it. NASA's next step in human exploration of the solar system, a trip to the red planet Mars, can be accomplished with one tenth the fuel payload for plasma vs chemical thrusters. That's the reason for all the excitement about high power electric propulsion! Examples of deep space missions using ion propulsion include NASA's successfully completed DS1 (Deep Space 1) which provided the closest view ever of a comet nucleus when it flew past Comet Borelly in 2001 and the DAWN Asteroid Orbiter which was successfully launched on September 2007. The highly ambitious DAWN mission to orbit the 2 most massive asteroids, Ceres and Vesta, is NOT possible using chemical thrusters. DAWN was the topic of my lecture at the 19 Oct 2007 General Meeting of AAI: "Launching Dawn: From be-hind-the-scenes at the Kennedy Space Center Press Site" and also my upcoming talk on 2 April 2008 at Rari-tan Valley Community College Planetarium at 7:30 PM (details elsewhere in this issue). Read the Nov 2007 issue of the Asterism which features my eyewitness account and pictures on the launch of DAWN and the complete list of my DAWN Launch Guest Blogs at the Weblog of The Planetary Society. Prof Choueiri and myself co-hosted Dr Marc Rayman from NASA's Jet Propulsion Lab when he presented a lecture on DAWN and DS1 and ion propulsion technology at the March 2006 monthly meeting of the AAAP astronomy club in Princeton. Dr. Rayman serves as Chief Engineer on both missions, DS1 and DAWN. Please check my blog report here, for the complete details of my interview with Dr. Rayman at the Kennedy Space Center about ion propulsion and DAWN: http://www.planetary.org/blog/article/00001160 All who attended the Plasma lab tour in Princeton were ecstatic at the opportunity to experience cutting edge research up close and personnel. We thanked Prof Choueiri, who also appreciated the enthusiasm and knowledge of our group. To learn more please plan to attend Prof Choueiri's exciting upcoming AAI lecture on 14 March 2008. Please contact me for further details: Dr. Ken Kremer Email: kremerken@yahoo.com NASA JPL Solar System Ambassador Photos from Plasma Lab Tour at Princeton University PHPP chamber (side view): Prof Choueiri gives us the "inside scoop" on a brand new research proposal he submitted to NASA on the day of the tour for a Plasma based Spectrometer to detect organic molecules on Mars. Photo Credit: Ken Kremer Left: Prof Choueiri describes EPPDyl lab history. The vacuum tanks were installed prior to constructing the Engineering building on top. Photo Credit: Ken Kremer Right: Lab tour group, including AAI members Ray Shapp and Steve Krisocki, enjoy Q&A with Prof Choueiri next to the LPDD. Photo Credit: Ken Kremer Left: Prof Choueiri explains how the Large Dielectric Pulsed Propulsion (LPDD) vacuum chamber facility (orange colored tank at right) contributes to pulsed propulsion and micropropulsion research since being brought online in 1998. Photo Credit: Ken Kremer Right: Lithium Lorentz Force Accelerator (LiLFA) Thruster: LiLFA is one of the most promising candidates for planetary exploration and heavy payload orbit raising missions. EPPDyL research deals with the basic physics at play in such devices and which require new theoretical models to be developed and tested. These research efforts are supported by The Jet Propulsion Laboratory (JPL) and focus on lithium safety and han- dling issues, the development of a mechanical liquid lithium feeding system, and integration and demonstration of the LiLFA thrusters. The Pulsed High-Power Diagnostic (PHPD) Facility: Perhaps the coolest looking chamber is the custom-made plexiglass chamber of the PHPD measuring 1.83 meters in length and 0.92 meter in diameter. The pumps maintain background pressure levels on the order of 10-5 torr for mass flow rates on the order of a few grams per second. Recent studies have included mass-injection split, thruster power scaling, discharge asymmetry characterization, anode power deposition and anode-region turbulence investigations. The mass injection system has been operated with various propellants including argon, xenon, krypton, helium, hydrogen and deuterium. Photo Credit: Ken Kremer