The Planetarium at UT Arlington

Ask the Astronomer Q&A

Tag: "physics"

• 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)
• What is a light year?
• A light year is a unit of distance. The distances to the stars are so great, it is inconvenient to use terms like miles or kilometers. So we use "light year." A light year is the distance a beam of light travels in a year. Light goes around 186,000 miles per second (in a vacuum) and in a year travels almost six trillion miles. Now, instead of saying Alpha Centauri is 25,000,000,000,000 miles away, it is much easier to say "around 4.3 light years" away. As a consequence, things we see in space are also removed from our own time. The light reaching Earth now from Alpha Centauri left 4.3 years ago. So we are actually seeing what the star looked like 4.3 years ago, even if we use a telescope. Other visible stars are dozens to hundreds of light years away, and the galaxies are millions and billions of light years away.
  
  (Tags:  light  physics)
• What's the difference between 3rd dimensional and 4th dimensional?
• The main physical difference between 3-dimensions (3D) and 4-dimensions (4D) is that 3D refers to space and 4D refers to space-time, which means that the extra fourth dimension describes time. It is important to point out that time and space must be combined together and considered on the same footing. We do live in 4D space-time, however, in every day life we experience 3D space and 1D time as two separate entities.
  
  (Tags:  albert einstein  physics)
• 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)
• 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)
• Why is the speed of light referred to as the letter "c"?
• The letter 'c' used for speed of light stands for 'constant', which means that the speed is the same in all inertial frames of reference. It has become common to use 'c' after the formulation of the Special Theory of Relativity by Einstein in 1905.
  
  (Tags:  albert einstein  light  physics)