Name: ________________________ DUE 8/30 ID number: ________________________

Homework 1. The Sun & You

As you have seen in class, astronomers often compare objects by taking ratios. For example, we might compare the masses of Jupiter and the Sun by taking the ratio of the Sun's mass to Jupiter's mass, and find that the Sun is about 1000 times more massive than Jupiter. In this assignment you will compare yourself to the Sun.

The Sun's diameter, mass, and age can all be found in the book, but for convenience the numbers you need are given here. Notice the small `S' below and after the diameter D, mass M, and age A; this `S' indicates that these quantities refer to the Sun.

Diameter: DS = 1.4 × 109 meters.
Mass: MS = 2 × 1030 kg.
Age: AS = 4.5 × 109 years.

Now fill in your `diameter', mass, and age below, or if you'd rather not reveal personal information, feel free to use make-believe numbers. To keep things simple, assume that your diameter is equal to your height, and your mass is equal to your weight. Here, the small `Y' labels quantities which refer to you.

Diameter: DY = ________________
Mass: MY = ________________
Age: AY = ________________

Now divide the Sun's diameter, mass, and age by your diameter, mass, and age. If you used feet and inches for your diameter, or pounds for your mass, then you'll have to convert these to metric units -- meters and kilograms -- before dividing. See Appendix A in the book for instructions on converting to metric units.

DS ÷ DY = __________________________________________________
MS ÷ MY = __________________________________________________
AS ÷ AY = __________________________________________________

So far, this has all been pretty straightforward, and if you know how to use scientific notation then you shouldn't have any serious problem. But now I'd like you to answer a few questions based on your results above:

1. In which way are you least like the Sun? That is, of the three things -- diameter, mass, and age -- used for this comparison, which one shows the greatest difference between you and the Sun? Briefly explain your choice.

2. In which way are you most like the Sun? That is, which thing shows the smallest difference between you and the Sun? Again, explain your choice.

3. Are you surprised by your answers to the two questions above? Why or why not?

Finally, if all this makes you feel small and insignificant in comparison to the mighty Sun, don't worry. We'll come back to this and discover that, in one very surprising way, human beings actually outclass the Sun.

Joshua E. Barnes (
Last modified: August 25, 1999