Grade 5 Science Practice Test: Sun, Stars, Shadows and Gravity

How bright a star looks depends a lot on its distance. The Sun is about 150 million kilometers away, while the next closest star is about 270,000 times farther. Many stars are bigger and give off more light than the Sun, but they look tiny because they are so far away.

If two stars give off the same amount of light, the one that is farther away looks dimmer, just as a flashlight looks dimmer from across a field than from across a room.

The stars are still there and still shining in the daytime. Sunlight scattered by the air makes the whole sky bright, so the much fainter light of distant stars cannot be seen until the Sun sets.

As Earth spins, the side facing the Sun has day and the side facing away has night. One full spin takes about 24 hours. Earth's trip around the Sun takes about a year, not a day.

The Sun only seems to move. Earth turns toward the east, so the Sun comes into view on the eastern horizon and drops out of view on the western horizon, the way trees seem to move backward when you ride in a car.

A shadow always points away from the light source. In the morning the Sun is low in the eastern sky, so the flagpole's shadow stretches toward the west. In the late afternoon it would point toward the east.

In the United States, the noon Sun is high in summer and much lower in winter. A lower Sun makes longer shadows, so the December shadow is longer. The time of day is the same, but the Sun's height at noon changes with the seasons.

Earth travels around the Sun once a year. In summer, Orion is on the same side of the sky as the Sun, so it is up during the day and hidden by sunlight; in winter, our night side faces it. The stars themselves do not move or stop shining.

One trip of Earth around the Sun, one orbit, takes about 365 days, or one year. About 24 hours is the time for one spin on Earth's axis, and about 30 days is close to the time the Moon takes to go through its phases.

Earth's axis points almost straight at the North Star. As Earth spins, the other stars seem to circle around that point, while the North Star hardly moves. The stars are not really orbiting the North Star.

Gravity is a pull between objects that have mass. Earth's gravity pulls everything near it toward Earth's center, which is why a thrown ball slows down, stops and falls back. Magnetism is a different force that acts only on certain materials.

Earth's gravity keeps pulling the Moon toward Earth while the Moon moves forward, so its path curves into an orbit. In the same way, the Sun's gravity keeps Earth in its orbit around the Sun.

Weight is the pull of gravity on an object. The Moon has much less mass than Earth, so its gravity is weaker, about one-sixth as strong, and the astronaut weighs less. Her mass stays the same, and the Moon does have gravity.

A low light source makes long shadows and a high one makes short shadows. This model shows why shadows are long in the early morning and late afternoon, when the Sun is low, and short around midday, when it is high.

Daylight rises from about 912 hours in January to about 15 hours in June, then falls to about 9 hours in December. The pattern repeats every year because of Earth's tilted axis as it orbits the Sun.