In the following we will show how to solve simple problems in astronomy.
One of the most common type of problem in astronomy (and everyday life, for
that matter) is the distance - velocity - time problem.
1. For example, suppose you are driving cross-country at an average speed
of 60mph. If you drive for 12 hours how far will you get?

A).. B).. C).. D).. E).. |

2. How did you solve that problem?

A)... B)... C)... D)... E)... |

Notice that you used the basic relation that Distance = speed x time, or mathematically, D=Vt, where D is the distance you traveled, V is your average speed (more technically the velocity), and t is the time you traveled.

Now let's do a variation on that problem.

3. Suppose you are driving from Boston to New York. If you travel at an
average speed of 50 mph and the distance is 250 miles, how long will the trip take?

A)... B)... C)... D)... E)... |

Notice that you again used the basic relation D=Vt, but now in the form time = distance/speed, or mathematically, t=D/V.

Let's now do an astronomical version of this problem.

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4. The space shuttle travels around the Earth in a circular orbit whose
circumference is about 25,000 miles. The shuttle's orbital speed is about
17,000 miles/hr. About how long does it take the shuttle to complete one
orbit around the Earth? (Notice this is exactly like the driving problem
above.)

A)... B)... C)... D)... E)... |

Notice that in this problem none of the answers you chose from were the answer you found mathematically. Rather, you were asked to choose from rounded off answers. Such rounding off is very important in writing out answers. Generally 3 digits is accurate enough for our purposes.

For example,

5. round off 2.7248283...to three figures.

A)... B)... C)... D)... E)... |

Let's now do another astronomical distance/velocity time problem.

6. A radar pulse is sent from the Earth to an asteroid, bounces off and returns to Earth. The radar pulse travels at the speed of light (300,000 km/sec) and takes 150 seconds to travel out and return. How far away is the asteroid? (Notice that this is exactly like problem 1 above.)

A)... B)... C)... D)... ^{7} kmE)... ^{7} km |

To better comprehend how much time the pulse takes, let's express the 150 seconds in minutes.

7. 150 seconds is about how many minutes? (As a quick check on your answer,
will the number of minutes be more or less than the number of seconds?)

A)... B)... C)... D)... E)... |

You will often have to make conversions of this sort in problems. For example, suppose we ask the following: How many years does it take a ray of light to travel from a star 12x10

In this problem you will get an answer in seconds, but you are asked for the answer in years. Thus, you need the number seconds in a year. You can figure that out by multiplying the number of seconds in a minute by the number of minutes in an hour by the number of hours in a day by the number of days in a year. In doing all that you will find that the number of seconds in a year is about 3 x 10

8. Given this conversion factor, what is the answer to the above problem?

A)... B)... C)... D)... E)... |

If you had trouble getting this answer, check your powers-of-ten math. For example,

9. what is 10 ^{13} divided by 10 ^{5} ?

A)...^{8}B)... ^{2.6} C)... ^{18} D)... E)... |

Your AnswersQ1: Q2: Q3: Q4: Q5: Q6: Q7: Q8: Q9: |
Your answer to the question wasQ1: Q2: Q3: Q4: Q5: Q6: Q7: Q8: Q9: |