The Moon is the only natural satellite of the Earth and the fifth largest satellite in the Solar System.
It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having 27% the diameter and 60% the density of Earth.
It is in synchronous rotation with Earth, always showing the same face.
It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a similar reflectance to coal.
The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to appear almost the same size in the sky as the Sun, allowing it to cover the Sun nearly precisely in total solar eclipses.
The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day.
The Phases of the Moon:
Topics covered in this snack-sized chapter:
- The full Moon always rises just after sunset.
- A crescent Moon sets shortly after sunset.
- The lit side of the Moon always faces the Sun.
The lunar cycle is the basis of the month.
- Different amounts of lit and dark sides over the course of a month can be seen in a lunar cycle.
A Lunar Eclipse occurs when the Moon passes directly behind the Earth into its umbra (shadow).
A Lunar Eclipse is seen when the Sun, the Earth and the Moon come in the same line.
When the Earth comes in between the Sun and the Moon.
The Moon passes through the Earth’s shadow.
The shadow of an object has two parts:
- The umbra: “complete” shadow
During a total lunar eclipse, the Moon passes through Earth’s shadow.
- The penumbra: “partial” shadow
Tides are caused by the difference of the Moon’s gravitational attraction on water on the Earth.
The forces are balanced at the center of the Earth.
Excess centrifugal force pushes water away from the moon on the far side.
The Sun is also producing tidal effects, about half as strong as the Moon.
Near Full Moon and New Moon, those two effects add up to cause spring tides.
Near first and third quarter, the two effects work at a right angle, causing neap tides.