Understanding Relationships How can it be that Earth is at perihelion during wintertime in the Northern Hemisphere?

Describe ways in which tides could be affected if Earth had two moons.

A $2150 \mathrm{~kg}$ satellite used in a cellular telephone network is in a circular orbit at a height of $780 \mathrm{~km}$ above the surface of the earth What is the gravitational force on the satellite? What fraction of this force of the satellite's weight is at the surface of the earth?

How far from Earth's center is the center of mass of the Earth Moon system?

The temperature at the surface of the Sun is approximately $5700 \mathrm{~K}$, and the temperature at the surface of the Earth is approximately $290 \mathrm{~K}$. What entropy change occurs when $1000 \mathrm{~J}$ of energy is transferred by radiation from the Sun to the Earth?

For about how many years of geological time have the dinosaurs existed on Earth?

What do we call the gravitational force between the Earth and your body.

How does ellipticity affect the total amount of solar energy that reaches Earth?

Describe the arrangement of the sun, the moon, and Earth during a solar eclipse and a lunar eclipse.

If a baseball were the size of Earth, about how large would its atoms be?

Does the Earth do any work on the Moon as the Moon moves in its orbit?

The orbital revolution of the Moon about Earth takes about 27.3 days and is in the same direction as Earth's rotation (24 h). Use this information to show that high tides occur everywhere on Earth every 12 h and 26 min.

A spaceship leaves Earth traveling at $0.65 c$. A second spaceship leaves the first at a speed of $0.82 c$ with respect to the first. Calculate the speed of the second ship with respect to Earth if it is fired in the same direction the first spaceship is already moving.

Briefly describe the basic characteristics that all living things on Earth have in common.