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Chapter 3: Problem 12

Why doesn't a lunar eclipse occur at every full moon and a solar eclipse at every new moon?

Short Answer

Expert verified
Lunar and solar eclipses don't occur at every full moon and new moon respectively because the Moon's orbit around the Earth is tilted about 5 degrees to the Earth's orbit around the Sun. Most of the time during the full and new moon phases, the Moon's position is such that it either overshoots or undershoots the Earth's shadow for a lunar eclipse or the Moon's shadow for a solar eclipse.

Step by step solution

01

Understanding lunar and solar eclipses

A lunar eclipse occurs when the Earth comes between the Sun and the Moon, and casts a shadow on the Moon. A solar eclipse happens when the Moon is between the Earth and the Sun, and the Moon's shadow is cast on the Earth. The Earth experiences day and night because it rotates on its axis, but the Moon orbits the Earth roughly once a month, causing the different moon phases we observe from Earth based on the amount of sunlight the Moon reflects back to us.
02

Why eclipses don't occur every month

Eclipses don't happen every full moon or new moon because the Moon's orbit around the Earth is tilted about 5 degrees relative to the Earth's orbit around the Sun. So, most of the time during full and new moons, the Moon is above or below the plane of Earth's orbit, causing the Sun's light to either miss the Earth's shadow or the Earth to miss the Moon's shadow.
03

When do eclipses happen

Eclipses can only happen when the Moon's orbit crosses the Earth's orbital plane (the line connecting the Earth and the Sun), a point known as a 'node'. If the Moon is at full phase and near a node, a lunar eclipse occurs because the Earth's shadow falls on the Moon. Meanwhile, if the Moon is at a new phase and near a node, it blocks the Sun's light causing a solar eclipse.

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Most popular questions from this chapter

The Moon is highest in the sky when it crosses the meridian (see Figure 2-21), halfway between the time of moonrise and the time of moonset. What is the phase of the Moon if it is highest in the sky at (a) midnight; (b) sunrise; (c) noon; (d) sunset? Explain your answers.

You are watching a lunar eclipse from some place on the Earth's night side. Will you see the Moon enter the Earth's shadow from the east or from the west? Explain your reasoning.

Suppose the Earth moved a little faster around the Sun, so that it took a bit less than one year to make a complete orbit. If the speed of the Moon's orbit around the Earth were unchanged, would the length of the sidereal month be the same, longer, or shorter than it is now? What about the synodic month? Explain your answers.

How many more sidereal months than synodic months are there in a year? Explain.

How would the sequence and timing of lunar phases be affected if the Moon moved around its orbit (a) in the same direction, but at twice the speed; (b) at the same speed, but in the opposite direction? Explain your answers.
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