# What is the mass of the Milky Way?

We can consider the Sun to be a satellite of the Milky Way. The Sun revolves around the center of the Milky Way with a radius of 8 kpc. The period of revolution is 230 million years. What is the mass of the Milky Way?

# A string around the Earth’s equator

Place a string around the Earth’s equator and pull it snug. Add a length of one meter to the string and push it away from the equator an equidistant amount. What is the largest animal, from the list below, that would now be able to walk under the string?

Flea Mouse Dachshund Calf Horse Elephant

# A geostationary satellite

A geostationary satellite is a satellite in geostationary orbit, with an orbital period the same as the Earth’s rotation period. The geostationary orbit is a circular orbit directly above the Earth’s equator.

How high above the Earth’s surface must the geostationary satellite be placed into orbit?

# How long would it take to fall through the center of the Earth?

We have a hole that leads straight through the center of the Earth. We neglect air resistance and assume that the Earth has uniform density ρ. How long would it take to fall through the center of the Earth and reach the other side of the planet?

# What is the surface temperature of the planet?

A planet of radius r and mass M has a homogeneous atmosphere (density independent of height). The atmosphere has a height h and the atmosphere’s gas has a molar mass μ.
What is the surface temperature of the planet?

# Why Is The Milky Way A Spiral?

More than two-thirds of the galaxies are disc shaped. Most disc galaxies have spiral arms and are called spiral galaxies. Continue reading

# If the orbital speed was doubled

Each planet has its own orbital speed. If the orbital speed was doubled, the planet would

a) enter into a closer orbit around the Sun.
b) enter into a far orbit around the Sun.
c) warm up.
d) escape the Sun.