# 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 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?

# If the solar system were reduced

If all the linear dimensions of the solar system were reduced in some proportion, then what will be the length of Earth’s year?

# A Satellite Orbits The Moon

Image Credit: NASA Ames/Dana Berry

A satellite orbits the Moon in a circular orbit. The radius of the Moon is 1.74×10^6 m , the mass of the Moon is 7.35×10^22 kg. Calculate the speed of a satellite in a circular orbit, very near the Moon’s surface.

# Moon, Sun Or Both About Equally

Image Credit: NASA

The Moon is most responsible for Earth’s tides. Which pulls more strongly on the Earth and its oceans?

A) Moon

B) Sun

C) Both about equally

Source: forum.understandingbasics