THE MOON

Satellites – natural or artificial bodies that revolve around larger bodies such as planets.

Except for Mercury and Venus, all of the planets have natural satellites called moons.

Earth’s moon is called Luna.

The lunar rocks brought back during the Apollo missions were found to be about 4.6 billion years old.

Because these rocks have hardly changed since they formed, scientists know the solar system itself is about 4.6 billion years old.

Before scientists had rock samples from the moon, there were three popular explanations for the moon’s formation:

1.) The moon was a separate body captured by Earth’s gravity.

2.) The moon formed at the same time and from the same materials as Earth.

3.) The newly formed Earth was spinning so fast that a piece flew off and became the moon.

When rocks brought back from the moon were studied, scientists found that the composition of the moon was similar to that of Earth’s mantle.

This evidence from the lunar rock samples supported the third explanation for the moon’s formation.

The current theory is that a large, Mars-sized object collided with Earth while Earth was still forming.

The collision was so violent that part of Earth’s mantle was blasted into orbit around Earth to form the moon.

From Earth, one of the most noticeable aspects of the moon is its continually changing appearance.

These different appearances of the moon result from its changing position relative to Earth and the sun.

The different appearances of the moon due to its changing position are called phases.

Waxing and Waning When the moon is waxing,

the sunlit fraction that we can see from Earth is getting larger.

When the moon is waning, the sunlit fraction is getting smaller.

Even as the phases of the moon change, the total amount of sunlight that the moon gets remains the same.

The positions of the moon, sun, and Earth determine which phase the moon is in.

Half the moon is always in sunlight, just as half the Earth is always in sunlight.

Because the moon’s period of rotation is the same as the period of revolution, on Earth you always see the same side of the moon.

Eclipse – an event in which the shadow of one celestial body falls on another.

A solar eclipse happens when the moon comes between Earth and the sun and the shadow of the moon falls on part of Earth.

The disk of the moon does not completely cover the disk of the sun.

A thin ring of sun shows around the moon’s outer edge.

When the moon is closer to Earth, the moon appears to be the same size as the sun.

During a total solar eclipse, the disk of the moon completely covers the disk of the sun.

A lunar eclipse happens when Earth comes between the sun and the moon and the shadow of Earth falls on the moon.

The view during a lunar eclipse is spectacular.

Earth’s atmosphere acts like a lens and bends some of the sunlight into the Earth’s shadow.

When sunlight hits the particles in the atmosphere, blue light is filtered out.

As a result, most of the remaining light that lights the moon is red.

The Moons of Mars

Mars’ two moons, Phobos and Deimos, are small, oddly shaped satellites.

They are very dark.

Scientists think that these two moons are asteroids caught by Mars’ gravity.

The Moons of Jupiter

Jupiter has dozens of moons.

The four largest moons – Ganymede, Callisto, Io and Europa – were discovered by Galileo in 1610.

They are known as the Galilean Satellites.

The Galilean satellite closest to Jupiter is Io.

Io is caught in a gravitational tug of war between Jupiter and Io’s nearest neighbor, the moon Europa.

This constant tugging stretches Io a little and causes it to heat up.

As a result, Io is the most volcanically active body in the solar system.

Recent pictures of the moon Europa support the idea that liquid water may lie beneath the moon’s icy surface.

This idea makes many scientists wonder if life could have evolved in the underground oceans of Europa.

The Moons of Saturn Saturn has dozens of moons. Most of these moons are small

bodies that are made mostly of frozen water but contain some rocky material.

The largest satellite, Titan, was discovered in 1655.

It appears to have a hazy orange atmosphere.

Earth’s early atmosphere may have been like Titan’s is now.

By studying Titan, scientists hope to learn more about how life began on Earth.

The Moons of Uranus

Uranus has several moons.

Uranus’s largest moons are made of ice and rock and are heavily cratered.

The Moons of Neptune

Neptune has several known moons, only one of which is large.

This large moon is Triton.

Triton

Triton revolves around Neptune backwards.

This orbit suggests that Triton may have been captured by Neptune’s gravity.

The atmosphere is very thin and made mostly of nitrogen gas.

The surface is frozen nitrogen and methane.

Ice volcanos eject nitrogen gas high into the atmosphere.

The Moon and the Tides

Tides are daily changes in the level of ocean water. They are influenced by the sun and the moon.

The gravity of the moon pulls on every particle of Earth.

But the pull on liquids is much more noticeable than on solids, because liquids move more easily.

How often tides occur and the difference in tidal levels depend on the position of the moon as it revolves around Earth.

The moon’s pull is strongest on the part of Earth directly facing the moon.

When part of the ocean is directly facing the moon, the water there bulges toward the sun.

At the same time, water on the opposite side of Earth bulges because of the rotation of Earth and the motion of the moon around Earth.

These bulges are called high tide.

The rotation of Earth and the moon’s revolution around Earth determine when tides occur.

The sun’s influence on tides is less powerful that the moon’s influence.

The combined forces of the sun and the moon on Earth result in tidal ranges that vary based on the positions of all three bodies.

A tidal range is the difference between levels of ocean water at high tide and low tide.

Spring tides are tides with the largest daily tidal range and occur during the new and full moons, or every 14 days.

Neap tides are tides with the smallest daily tidal range and occur during the first and third quarters of the moon.

After a tidal range has been measured, the times that tides occur can be accurately predicted.

In some coastal areas that have narrow inlets, movements of water called tidal bores occur.

A tidal bore is a body of water that rushes up through a narrow bay, estuary, or river channel during the rise of high tide and causes a very sudden tidal rise.

Tidal Bore