|
|
|
|
|
the Net Updated Weekly Moon Meteorite - Moon rock found on earth. - MSNBC, August 18, 2000. Linear Breakup - Hubble images record the event. - CNN, August 10, 2000. National Security Agency Files Released - UFO hunters hope to find evidence of ET. - CNN, August 8, 2000. Save Pluto - Congress may cut budget. - CNN, July 29, 2000. 2004 Mission to Mars - NASA unveils plans. - ABC, July 28, 2000. Parts Break Off Comet - Hubble Space Telescope took pictures of Comet LINEAR. - ABC, July 28, 2000. Supernovae Spreads Key Elements of Life - Chandra X-ray Observatory shows details. - SSN, July 18, 2000. Comet Linear - Update on path of a comet you can see with binoculars. - BBC, July 17, 2000. New Type of Solar Flare - NASA's Chandra X-ray Observatory discovered a solar flare that is not a brown dwarf, or failed star. - SSN, July 12, 2000. Large Impact Crater Found on Europa - The Crater is the size of a city. - BBC, July 11, 2000. Black Hole’s Spotlight - Picture shows Galaxy M87 with electrons and other subatomic particles coming from the galaxy's center. - MSNBC, July 7, 2000. Solarmax - New IMAX film. - CNN, July 4, 2000. Gamma-Ray Burst Found Where Stars are Being Born - Intense radiation explosion are caused. - CNN, June 30, 2000. Water on Mars - Update. - SSN, June 29, 2000. Astroid Map - Astronomers are keeping track of near-Earth asteroids. - ABC, June 28, 2000. Information Collected on Martian Oceans - Evidence suggests it may have been a salt water ocean. - ABC, June 23, 2000. Asteroids May Have Seasons - Sun will rise over the south pole of asteroid Eros. - SSN, June 21, 2000. August 15 - Full Moon August 22 - Last Quarter August 29 - New Moon Skywatching Center - Current Month's Skies. Astronomy Magazine - This Month's Sky Show. Sky & Telescope - August 2000 Skies. Meteor Showers for August Alpha Capricornids (CAP) Duration: July 15-September 11 Peak: Aug. 1-2 Southern Iota Aquarids (SIA) Duration: July 1-September 18 Peak: Aug. 6-7 Perseids (PER) Duration: July 23-August 22 Peak: Aug. 12 Northern Iota Aquarids (NIA) Duration: August 11-September 10 Peak: Aug. 25-26 
30 years ago Two Micron Sky Survey (TMSS; Neugebauer & Leighton 1969) scanned 70% of the sky and detected ~5,700 celestial sources of infrared radiation. This was the last large-area near-infrared survey of the sky was carried out. Technology has greatly improved since the last sky survey. New infrared detectors can now detect astronomical objects over 100 million times fainter than those detected in the TMSS. The Two Micron All Sky Survey (2MASS) project, with this new technology, will once again map the skies. 2MASS will obtain a large-scale structure of the Milky Way. Using space infrared telescopes such as HST/NICMOS, the Space Infrared Telescope Facility (SIRTF), and the Next Generation Space Telescope (NGST), and ground infrared telescopes such as Keck I, Keck II, and Gemini, will provide the detail information needed to map our galaxy. The University of Massachusetts (UMass) heads the overall management of the project, and for developing the infrared cameras and on-site computing systems. The Infrared Processing and Analysis Center (IPAC) is in charge of all data processing through the Production Pipeline, and construction and distribution of the data products. 2MASS is receiving funding from National Aeronautics and Space Administration (NASA) and the National Science Foundation (NSF). 2MASS will create: An unprecedented view of the Milky Way nearly free of the obscuring effects of interstellar dust, which will reveal the true distribution of luminous mass, and thus the largest structures, over the entire length of the Galaxy. A digital atlas of the sky comprising approximately 4 million 8´ × 16´ Atlas Images, having about 4´´ spatial resolution in each of the three wavelength bands. A point source catalog containing accurate positions and fluxes for ~300 million stars and other unresolved objects. An extended source catalog containing positions and total magnitudes for more than 1,000,000 galaxies and other nebulae. 2MASS will release the data products on the approximate schedule: The 2MASS Sampler of one northern night's of data (63 square degrees of sky). The First large Incremental Release of northern hemisphere data occurred in 1999 Spring. This release covered about 2483 square degrees, i.e., ~6% of the sky. The Second large Incremental Release - Now Available! - of northern and southern hemisphere data in 2000 Winter. This release covers more than 19,600 square degrees, i.e., ~47% of the sky. Incremental releases every 6 months to 1 year thereafter, of both northern and southern hemisphere data. Each night of released data will consist of about 250,000 point sources, 2000 galaxies, and 5000 images, or, equivalently, about 0.5 GB of data. The Catalogs alone for the Second Release consist of more than 65 GB of uncompressed data. The Survey, when completed and fully processed, will consist of about 2 TB of catalogs and compressed images. 2MASS web site is well worth a visit. It will take some time to load some of their detailed pictures. Atlas Image obtained as part of the Two Micron All Sky Survey (2MASS), a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. The above photograph is of the Center of our Milky Way Galaxy. Now you can get Free Email that shows you enjoy astronomy. You can use your name, (yourname)@astronomydigest.com . Or, you can use an astronomy name like orion@astronomydigest.com . Right now there are many names available. I only ask that if you get an account that you plan to use it. And, if you no longer plan to use it, you simply delete it. This will help keep the astronomy names available for others to use. I am very pleased to offer this service for Free. To get your Free Email account use the Free Email box located at the top right column on this ezine. 
Astronomy Digest Help support "Astronomy Digest" and get paid for doing it. All Advantage is a program that puts a banner at the bottom of your screen. They rotate ads when you are on the internet. You get paid 50 cents per hour. When you get someone else to join, you get 10 cents per hour for each hour they are earning 50 cents. So you can earn money and help support "Astronomy Digest" at the same time. Join Here I would like to thank everyone who is earning money and helping to support Astronomy Digest through AllAdvantage. I am actually receiving checks from them. I also find myself clicking on their banners and going to places on the web that I would have never found. Thanks again.  Solar Filters . In 1610, Galileo was the first to observe the sunspots with his new telescope. Daily observations were started at the Zurich Observatory in 1749. Currently there are two "official" sunspot numbers reported. The International Sunspot Number is compiled by the Sunspot Index Data Center in Belgium, and the NOAA sunspot number is compiled by the US National Oceanic and Atmospheric Administration.  Sunspots occur over an 11 year cycle. During this 11 year cycle the number of sunspots seen on the Sun increases from nearly zero to over 100, and then decreases to near zero again as the next cycle starts. This year, and next year, will be the peak time for sunspots. If you are interested in observing sunspots using your telescope, you will need a solar filter and a low power eye piece. Solar filters can be purchased at your local astronomy store. Never use your telescope to look at the sun, without a solar filter. The filter must be specially designed to look at the sun using a telescope. Otherwise, eye damage will occur. Never look directly at the sun without proper eye protection. See your eye doctor for details. 
Mars: Uncovering the Secrets of the Red Planet National Geographic presents a state-of the-art report on the planet itself, the technology that allows us to explore it, and the prospects for further exciting discoveries. Mars includes a stunning, three-dimensional, eight-page panoramic gatefold with images that capture the genuine wonder of discovery at the Pathfinder landing site. With an authoritative text by Paul Raeburn, an award-winning science journalist, and a foreword and insightful commentary by Matt Golombek, chief scientist on the hugely successful Pathfinder mission, Mars traces the long history of our fascination with the red planet, explains the current state of Mars exploration, and interprets the amazing images transmitted across the vastness of space in clear, easy-to-understand language.
|
Barnaveddoge – a 4,000-year-old astronomical marker. By Anthony Murphy and Richard Moore This stone is one of a pair on the Barnaveddoge ridge – the other, measuring 3.2m in height, is the tallest standing stone in this part of the country. These stones are among 40 in County Louth. But the small stone at Barnaveddoge is a very special astronomical and calendrical device, recording no fewer than four major solar events in the calendar. The stone is shaped like a square in section, but is oriented so that the corners face roughly north, south, east and west. The flat sides of the stone can be used as viewing lines, just as many of the standing stones in Ireland have flat sides which point towards significant risings and settings of the sun. It was on the evening of June 19th, two days before the Summer Solstice, that we visited the stones – just in time to witness a spectacular Summer sunset which occurred directly in line with one of the straight edges of this stone. We took detailed notes and some photographs of the event and made further measurements which showed that the stone has a very unique system of alignments. The Summer Solstice sunset occurs diametrically opposite to the position of the Winter Solstice sunrise, so immediately we knew we had a stone which marked two very important calendrical moments. But we further discovered that another of the straight edges of the stone is aligned to the position of the rising sun on Summer Solstice, therefore also marking the Winter sunset. It is this double alignment which makes Barnaveddoge special among ancient sites. At Baltray, for instance, which is located at the mouth of the Boyne River some 20 miles away, a large, flat standing stone points to Rockabill Island and marks the position of the rising sun on Winter Solstice. It also marks Summer sunset, but it does not mark the other line – Summer sunrise and Winter sunset. Another stone which we found to have an astronomical alignment is one at Drumshallon, where this flat monolith has been aligned directly East-West, marking sunrise and sunset on the equinoxes. These standing stones are located in a andscape which is literally littered with ancient sites which have an astronomical and calendrical function. Only 15 miles from Barnaveddoge lie the huge burial mounds of Newgrange, Knowth and Dowth, all of which have been shown to contain alignments on the Solstices and Equinoxes. Also, a massive embanked enclosure, or henge site in the Boyne Valley has openings which are aligned on the Summer Solstice sunrise and Winter sunset. The construction phase of Newgrange began around 3,150 BC, so it seems the ancient people of the Boyne Valley region were astronomically astute long before the great stones were hauled into place at Stonehenge in England, and a whole thousand years before the great pyramids of Giza were constructed. In light of the number of ancient sites in the area with astronomical alignments, much debate has centred on the reasons for the construction of these monuments. At Newgrange, where the sunlight penetrates the central chamber briefly on the morning of Winter Solstice, it is believed the purpose for this tied in with cremation and burial ceremonies at the great mound, and that somehow the soul of the deceased was transferred from Earth to Heaven in this great moment. One thing which can be said with certainty about the Boyne sites is that their builders were very aware of the celestial movements, and had a great consciousness of the seasons. At Knowth there is a 5000-year-old carved stone which showed the builders to be aware of what we call the “Metonic Cycle” of the moon. At nearby Dowth there is a stone which features representations of a heliacal rising of the Pleiades. The Barnaveddoge discovery is our fourth astronomical discovery in 18 months, and we plan to continue our research into the amazing prehistoric astronomers of the Boyne Valley for a long time to come. For more information on Barnaveddoge visit the Mythical Ireland website. I found this to be an enjoyable web site if you like astronomy or history. It is worth a visit. If you have an astronomy related article you would like to have published, email it to Astronomy Digest. 
by William H. Clark II The Russians never did reach Mars, in half a dozen attempts. Lately, the U.S. is 0-for-2 in reaching the Red Planet. Gambling that the problem is in the flight path, Bill Clark, a Ph.D. student at the University of Texas at Austin, has written a computer simulation of the Earth-to-Mars trajectory. As it turns out, Mars is as intractable in model space, as it is in real space! Mission: Mars Clark’s first attempt at a computer simulation was two years ago for his Master’s Thesis. The model of the trajectory is quite complex to program, with many intricate, interdependent schemes. The only way to know your simulation is correct is to compute the Jacobi Integral for each iteration. This is a measure of the energy of the spacecraft and should remain constant. The value was not constant in Clark's routine, though, and the program had to be discarded when, months later, the cause was still unknown. So, the first question his advisor asked when told of the new program was, “Is the Jacobi Integral constant?” Dr. Roger Broucke, professor emeritus in the Aerospace Engineering Department at Texas, is an expert in Celestial Mechanics. His forte’ is the Three Body Problem (3BP), the most famous unsolved problem in the history of mathematics. The Mars trajectory is a Four Body Problem: Sun, Earth, Mars, and the spacecraft (s/c). Only a half dozen papers have ever been written on the 4BP. Dr. Broucke suggested a new, analytical approach based on the notion that there is a point in every Mars mission trajectory where Earth and Mars are along the same straight line from the Sun. This alignment is called conjunction (see Figure 1). He had Clark divide the trajectory into two 3BP's that could be evaluated independently: Sun-Earth-s/c and Sun-Mars-s/c. The equations of motion are integrated backward in time from conjunction to reach Earth; and forward in time from conjunction to reach Mars. Optimization The problem is set up for a basic Hohmann Transfer on which, as indicated in the figure, the spacecraft (s/c) leaves Earth on the positive x-axis and arrives on the negative x-axis. This is the standard, lowest energy trajectory. What if we want to get to Mars faster, as indicated by the dashed line? Well, you must speed up somewhere along the path. The best place to increase velocity on an elliptical path is at an angle of 90 degrees (ie when the s/c crosses the y-axis in the Figure). This is exactly where the s/c is when the planets are at conjunction, so it is a perfect place to add velocity since the problem is already segmented there. Theoretically, the thrust can be applied in a magnitude and an angle, going both toward Earth and toward Mars. This gives four variables with which to vary the flight path. The problem is still quite difficult to solve, though, so the computer program varies only the two thrust parameters going to Mars. The computer program is a Fortran routine compiled into a windows executable file. It can be downloaded free from http://get-me.to/mars When you run the program, it prompts you for the two inputs: magnitude and direction of the mid course thrust correction. The best scenario so far is with a 0.9 km/sec thrust at 0 degrees. You try something close to these values. A minute or two later two pages of sixteen digit numbers careen down the screen (see Figure 2). You can scroll up to review the whole listing, or save the data to a file. Either way, though; what do they all mean? First, a little more theory. The Problem To optimize something you must have the same beginning and end point for all cases. Here, the s/c starts from a 200 km parking orbit around Earth and finishes on a 100 km parking orbit around Mars. The next thing to realize is that the Earth-to-Mars trajectory is three problems juxtaposed: (1) a hyperbolic escape trajectory with Earth as the central body, and the Sun as a perturbing third body (2) an elliptical transfer orbit from Earth to Mars, with the Sun as the central body and Earth and Mars as perturbing third bodies (3) a hyperbolic capture trajectory, with Mars as the central body and the Sun as the perturbing third body Where “central body” is the one with the greatest gravitational force on the s/c. For example, when closest to Earth, the foci of the orbit is Earth. The Sun, though weaker by comparison, still exerts a strong enough force to “perturb,” or physically change, the path of the spacecraft. The transition between these regimes is called the “Sphere of Influence” (SOI). There is one centered at Earth, another at Mars. At Earth SOI the forces on the s/c due to the Sun and the Earth are equal. Similarly, the gravitational pull of Sun and Mars are equal at Mars’ SOI. The program integrates the entire trajectory numerically, using a Rung-Kutta variable step integrator to compute the position of the s/c to 1/10th of a centimeter accuracy. The path is integrated in either direction from conjunction, through the SOI and down to a point close to the planet. The numerical integration stops then and the program computes a simple minimum energy transfer to the final parking orbit. This is the typical five thrust Mars mission profile used by NASA. They maneuver carefully from the initial Earth parking orbit, using very little energy, to a point where a large enough thrust is applied to escape Earth’s gravity. Similarly, when approaching Mars, there is a large thrust followed by one or two small maneuvering thrusts, to get the s/c to a stable parking orbit around Mars. End Game The key to remember about reaching Mars is that the s/c is going only about half as fast as Mars. So the only way to intercept Mars is to get ahead of the planet, at as oblique an angle as possible. If you are just a little too slow, Mars skips ahead of you and you’re lost in deep space. If you are too far ahead, you either zoom off into never-never land, or Mars zooms right into you. A more elegant solution, for the less venturesome, is to apply very little extra thrust at conjunction (if you apply negative thrust, or at too high an angle, the s/c passes inside of Mars’ orbit altogether and goes into its own heliocentric orbit). Then, as the s/c approaches Mars near the negative x-axis, it nudges into Mars’ SOI, after which time it’s in orbit around Mars. Geometrically, the s/c just follows Mars around on its ellipse and stays there for two or three months before inching close enough to Mars to ease nonchalantly into the final parking orbit. “Mars Pathfinder” is not a passive game. You need to draw pictures, plot points, and think about coordinate systems in two or three dimensions. These are all the convolutions the experts go through, though. Who knows, perhaps you’ll find a better solution than NASA. Bill Clark is a fourth year doctoral student in Celestial Mechanics at UT Austin. As the last grad student in the major (Dr. Broucke, now retired, was the last CM professor), he still hopes that someone else will take the plunge.
|
(yourname)@astronomydigest.com 
|
|
|
|
Promote Your Site
|
|
|
|
|
|
|
|