Greetings, greetings fellow email readers, Here's your reminder -- AAS meeting Friday December 1st, 8:00pm, in room 302 of the aerospace building. * * * For anyone who missed the November meeting, you missed some of the most beautiful hi-res images from Hubble of the star forming regions in M-16 shared by Rhon at his SUN workstation.. * * * Well , it's just over a week now until Galileo sends its probe into the Jovian atmosphere. It's certainally had its share of problems. Let's hope all goes well. Can anyone with access to NASA Select tape it for a future meeting??? Here is a file from JPL giving "Galileo Amazing Facts": A new amazing fact about the Galileo mission to Jupiter appears on the Galileo home page every day: http://www.jpl.nasa.gov/galileo/ . Here are the Galileo amazing facts that have appeared so far: The Galileo probe weighs 339 kilograms (750 pounds) and will enter the atmosphere at a top speed of 170,000 kilometers per hour (106,000 mph), or about 50 times faster than a bullet shot out of a rifle. The probe will experience deceleration forces as high as 230 times Earth's gravity. In about two minutes, the orbiter's speed will be slowed to about 1,600 kilometers per hour (1,000 mph) as it begins its 75-minute mission to measure the planet's atmosphere and clouds, while descending into the dense atmosphere under its parachute. It's possible that the probe will also encounter lightning and rain. ------------------------------------------------------------------------------- Engineers have taken several steps to boost the performance of the ground antennas that will be receiving Galileo's signals. One trick is to use arrays of antennas instead of single antennas. How big (in diameter) would a single antenna be to provide the same performance as, say, the combination of the Canberra Deep Space Network site, the Parkes Radio Telescope, and the largest Goldstone antenna? 125 meters (410 feet)! That's about the distance from home plate to the wall in center field in Shea Stadium! ------------------------------------------------------------------------------- There's usually not that much dust for Galileo to plough through: a 1300 square foot house has maybe 290 cubic meters of space inside (about 10,000 cubic feet). At a usual interplanetary dust density of .00006 particles per cubic meter, you'd find one particle of dust in every 57 houses! Equivalently, that's the volume that you'd get if you covered a football field with a 4 meter high roof-- and you'd only find one dust particle in that entire volume! ------------------------------------------------------------------------------- How big are those dust motes that were slowing Galileo? The dust motes are .01 to .1 micrometers in diameter, which is 1/100th to 1/10th the size of airborne dust that you might see floating in sunlight in front of a window, or, several hundred times smaller than a human hair. ------------------------------------------------------------------------------- Galileo was somewhat slowed by having to plough through a dust storm originating from Jupiter--after three weeks, Galileo's speed dropped by a whopping 25 angstroms per second (1 angstrom is one ten-billionth of a meter, or about 4 billionths of an inch)! ------------------------------------------------------------------------------- The Galileo spacecraft is designed to survive extreme environmental hardship. The temperatures on various parts of Galileo can range from -220 to +220 degrees celsius. The average radiation dose per minute absorbed by Galileo during its orbital mission is equivalent to what the average person receives in a whole year on Earth. On 7 December, as it makes its closest approach to Jupiter, the radiation dose per minute to Galileo will exceed by several times what a person on Earth would receive in their entire lifetime! ------------------------------------------------------------------------------- Jupiter's volume is about 1,400 times that of the Earth. In fact, its volume is half again bigger than all of the Solar System's other planets, moons, asteroids, and comets combined. ------------------------------------------------------------------------------- The radio signals from Galileo will be incredibly weak (about a billion times fainter than the sound of a transistor radio in New York as heard from Los Angeles). Radio science tries to measure effects that are very minute (about the same as measuring the distance between Los Angeles and New York to the accuracy of a human hair). ------------------------------------------------------------------------------- It's not necessarily true that the shortest distance between two points is a straight line: as of November 15, 1995, Galileo still has 9,329,160 kilometers to travel along the curved arc that will take it to Jupiter. However, if you drew a straight line between the spacecraft and Jupiter on November 15, they'd be separated by 16,141,701 kilometers. What's going on? If Galileo headed out for where Jupiter is right now, it would arrive to find Jupiter long gone--the planet's orbital motion would have carried it further along its path around the Sun. Instead, the spacecraft is heading towards the point where its trajectory and Jupiter's orbit will intersect. Since Jupiter's speed going around the Sun is much faster than Galileo's current speed with respect to the Sun, Jupiter's orbital motion will eat up much of the distance between spacecraft and planet. That means that Galileo itself doesn't have to travel as far. ------------------------------------------------------------------------------- Galileo has already bagged a number of scientific firsts, including: the first close-up look at an asteroid (Gaspra), the first discovery of an asteroid moon (Ida's moon Dactyl), the first and only documented direct observation of a collision between solar system bodies (the impact of Comet Shoemaker-Levy 9 with Jupiter), and the first global scale multi-spectral (i.e. using several different wavelengths of light) imaging of the Moon's far side. ------------------------------------------------------------------------------- Typical home insulation has a rating R=19, and is 4" thick. Galileo's insulating blankets are 3 times as effective, and 1/20th the thickness (2/10ths of an inch thick). The spacecraft insulation is 65 times "better" than the fiberglass insulation that you'll find in your home! ------------------------------------------------------------------------------- Since Galileo is going into orbit around Jupiter (unlike the two Voyager spacecraft, which flew by the planet), it can fly by Jupiter and its moons at far closer distances than did Voyager, which means that Galileo's pictures will be a dramatic improvement over those from Voyager. Comparing Voyager images with those to be sent back from Galileo is like viewing a book at the base of the Empire State Building from the top story, as opposed to holding that book in your hands. ------------------------------------------------------------------------------- Galileo's power sources, radioisotope thermo-electric generators, are putting out only about 520 watts on 7 December. That's not even enough to run a kitchen toaster! * * * A Puzzler (from the ASTRO Mail List) : Who am I, what did I do, what did I predict? In the days of yore, I wrote before those tiny things were found. And in advance,without a glance, envisioned both go round. Only fiction? Firm prediction, with orbits neatly bound? But years must pass. Then through a glass they'll prove my vision sound. Hints: in fact he was (past tense) a great English novelist and to my knowledge was not an astronomer. * * * Did anyone else catch the lunar occultation of beta CAP Sunday evening? See you at the meeting, Russell Russell Whigham rwhigham@mont.mindspring.com