The Planetarium at UT Arlington

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• When will the Milky Way collide with Andromeda? Are those estimates accurate?
• The Andromeda Galaxy will collide with the Milkyway in 3 billion years as they are separated by 2.2 million light years and approaching to each other at approximately 500,000 km/hour speed. Are those numbers accurate? Yes and No. We measure distances and velocities accurately. That would allow us to give a specific date and time for the collision, if the galaxies were like solid objects. However, galaxy collisions are not similar to collision of 2 vehicles. Galaxies don’t have sharp boundaries that you can tell when the collision starts. Moreover, the collision will last approximately 1 billion years. During the collision, it is unlikely that any star will run into another! If there is life on a planet at that time, probably the life will not be affected. After the collision, galaxies change their shape, they either merge or form 2 “new” galaxies orbiting each other. Based on scientific data, numerous simulations have been computed and galaxy collision animations created. More specific information and animations can be found at the following link: http://www.galaxydynamics.org/tflops.html
  
  (Tags:  andromeda galaxy  milkyway galaxy  physics  star  universe)
• What is the best place and time to see a meteor shower?
• Meteors, sometimes called falling or shooting stars, are very common in the night sky. As Earth orbits around the Sun, it goes through debris fields, left behind by comets and other celestial objects and events. This debris falls towards the Earth, and burns up as it falls. That's what we see as a meteor. When the Earth goes through a large debris field, we can expect to see more meteors. Sometimes as many as 100 per hour. The Perseid meteor shower, which occurs every year in August, is one of the best meteor showers. To see the most meteors, go outside after midnight, when the sky is its darkest, and watch the show. Meteors will fall from all directions, but often they appear to start at one central point. In the case of the Perseid meteor showers, the meteors all appear to come from the constellation Perseus. If you can, get far away from the city to see the best possible show.
  
  (Tags:  earth)
• Why is the earth not at 0° solar longitude on March 21 (the vernal equinox, 1st day of spring), but at 180°? Confusingly, the vernal equinox supposedly marks the 0°
• In the diagram (http://ssd.jpl.nasa.gov/?ss_inner), Earth is about at 90 degrees, if you consider the vernal equinox at +X-axis. On March 21, Earth would be at 180 degrees, just like you said. Now, why Earth is not at zero degrees since it is vernal equinox? Because we determine equinoxes according to the Sun’s position, not Earth’s. Put Earth on the Vernal Equinox point (180 degrees). Which direction you see the Sun?
  
  (Tags:  earth  physics  sun)
• Every leap year, we add a compensatory day. In the interim, why is our official time never off by one-quarter or three quarters a day?
• The Earth orbits the sun once every 365.25 days, so every four years we add an extra day to the year (Leap Year). In the interim years we don’t have our “official” time off by any certain amount because each day is only off by 360 min/year. So to have an accurate “official” calendar, all we have to do is add an extra minute to each day, so that every day is 24 hours and 1 min. This number is so insignificant that we don’t calculate it in to our normal calendar, but over time, it will start to add up (1 day every 4 years), so that is why we add the leap day, but do not keep track of the time in the interim.
  
  (Tags:  earth)
• If I were to fast-forward into the future, and I was setting up a base on Callisto, what might be the best place to do that? Would somewhere like in the Lofn crater be a good place to put it? If so, what would the area look like? Would I be able to see Jupiter from there? Would the ground feel and look like snow? Would the thin atmosphere carry any sort of sound?
• Callisto is a tidally locked moon which means that the same side is always facing Jupiter (like our Moon). Unfortunately, the Lofn crater is located on the far side the moon (56˚ S and 23˚W) so your base would never see Jupiter. The surface of Callisto is covered by ice (water ice), carbon-dioxide and silicates; so it wouldn’t feel like snow, it would feel like hard ice. The thin atmosphere is so tiny; you can almost consider there is no atmosphere. It is surprising that this tiny moon has an atmosphere; however, it is not stable. The atmosphere is actually running away and is probably being replenished by the surface carbon-dioxide. Such an atmosphere wouldn’t carry any sound.
  
  (Tags:  jupiter  moon  physics  solar system)

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