# The Sun & You: Discussion

Most people did pretty well. One error which several people made was to write 101 (= 10) when they should have put 100 (= 1); for example,

 1.75 × 101 m = 17.5 m = 57.4 ft

Another somewhat common error was to mix units, for example:

 (4.5 × 109 yr) ÷ (5.7 × 108 sec) = 7.9 (yr/sec) = 7.9 × (3.15 × 107) = 2.5 × 108

My `diameter' (height), mass (weight), and age are:

 Dy = (6 ft) × (0.3048 m/ft) = (6 × 0.3048) m = 1.83 m My = (185 lb) × (0.454 kg/lb) = (185 × 0.454) kg = 84 kg Ay = 50 years

Dividing the Sun's diameter, mass, and age by my diameter, mass, and age, I obtain:

 D ÷ Dy = (1.39 × 109 m) ÷ (1.82 m) = 7.6 × 108 M ÷ My = (1.99 × 1030 kg) ÷ (84 kg) = 2.4 × 1028 A ÷ Ay = (4.5 × 109 years) ÷ (50 years) = 9.0 × 107

Note that the units cancel out, so the final numbers don't depend on the units used. I would have got the same final numbers with any choice of units, as long as I use the same units for myself and the Sun.

1. In which way are you most like the Sun?

• I'm most like the Sun in terms of age; the Sun is only (only???) about 108 times my age.

2. In which way are you least like the Sun?

• I'm least like the Sun in terms of mass; the Sun is about 2.4 × 1028 times my mass.

3. Are you surprised by your answers to the two questions above?

• The fact that the Sun is `only' about 108 times my age still seems amazing to me. I'm not surprised that mass shows the largest difference; for objects of similar density, mass is proportional to volume, and volume is proportional to the cube of diameter.