Practice with Calculations - Time and Distance in Astronomy

The appendices at the back of your textbook have a lot of useful information, including reviews of simple problem solving. Read through them if you need to brush up on topics such as units or scientific notation.

The following practice calculations should be completed before Thursday May 10, 2018. Given below is the speed of light and three useful conversion factors, where LY = light year and AU = astronomical unit. Aim for organization, accuracy, neatness, and clarity. Always show your work (the various steps) for maximum credit.

  • Speed of light = 186,000 miles/ sec = 300,000 km / sec
  • 1 LY = 63,240 AU
  • 1 AU = 9.29 x 107 miles = 1.50 x 108 km
  • 1 LY = 5.88 x 1012 miles = 9.46 x 1012 km
1. How long does it take a beam of light, such as a radio signal, to travel from an Earth laboratory to a spacecraft on Mars, a distance of about 35,000,000 miles (56,000,000 km)?

2. How many years would an "astro car" moving at 60 miles/hour (100 km / hour) need to cover the above distance?

3. If a radar beam, moving at the speed of light, needs 12 seconds to go from the Earth to a comet and back, then how far away is the comet?

4. M33, alias the Triangulum Galaxy, is about 2,400,000 light years away. (a) How many AU away is M33? (b) How many miles away is M33?

5. Sirius, the brightest night-time star, is 8.58 light years from the Earth. (a) How many AU from the Earth is Sirius? (b) How many years would a beam of red laser light need to reach Sirius?

Answers are here!
  • Pages maintained by Dr. Reggie Hudson
  • Last changed: December 8, 2015