Question

Knowing without touching.
Even before we sent spacecraft to the planets, we knew a lot about them from telescopic observations. Temperature, composition, etc. you can get from the spectrum. Let's look at how we can figure out other things.. Give a short description of how it could be done--a couple of sentences is enough. Write down any equations you need to use.

(2 pt.) (a) How could you determine the distance from a planet to the Sun?

(2 pt.) (b) How could you measure the size in km? You can measure the angular size (in degrees, arc minutes or arc seconds) with a telescope. Then use the distance found in part (a) above and convert the distance to km. The size in km can be determined from the distance in km and the angular size--HOW?

(3 pts.) (c) How could you determine the mass of another planet, making observations from Earth?

(1 pt.) (d) From the above observations, how could you determine the density of the planet?

(1 pt.) (e) Why is it useful to know the mean density of a planet?

Answer 1

a) using parallex method we can find the distance.

the angular size of telescope=

the diameter of sun=D

so the distance

b)

the convert the distance to the Km

c)

First we must calculate the mass of the Earth, to do this we can calculate the planet'sphysical radius from the distance, d, and its observable angular diameter,

radius

then yse the Newton's law of gravitation

then use Newton’s version of Kepler’s third law and rearrange the equation to find the mass of the planet

d)

The average density of a planet can be determined by dividing the mass of the objectby the total volume of the object

volume of the planet

so density

e)

The average density of a planet is a good indicator of what it's composed of, or how the interior might be structured.