Lunar eclipse

Lunar eclipse

Lunar eclipses occur when the Moon passes through the shadow cone of Earth

Geography

Keywords

lunar eclipse, Moon, shadow cone, penumbra, umbra, full moon, orbiting of the Moon, synchronous rotation, orbit of the Moon, orbital plane, Sun, Earth, astronomical object, astronomy, geography

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Questions

  • What is the relative position of the Sun, the Moon and the Earth during a lunar eclipse?
  • In which phase is the Moon when a lunar eclipse occurs?
  • When can we observe a lunar eclipse?
  • Do lunar eclipses occur at every Full Moon?
  • How often do lunar eclipses occur?
  • Do the orbital planes of the Earth and the Moon coincide?
  • Is it true that the Moon is in synchronous rotation with Earth?
  • Is it true that we always see the same side of the Moon from the Earth?
  • Is it true that the Moon must be located on or near the Earth's orbital plane for a lunar eclipse?
  • Is it true that the Moon has light of its own?
  • Is it true that lunar eclipses do not only occur during the Full Moon phase?
  • When does a lunar eclipse take place?
  • What does the term 'synchronous rotation' refer to?
  • How long does it take for the Moon to complete one orbit around the Earth?
  • What is the umbra?
  • What is the penumbra?
  • When does a full lunar eclipse occur?
  • When does a partial lunar eclipse occur?
  • What colour does the Moon appear during a lunar eclipse?

Scenes

Position of the Sun, the Moon and the Earth

  • Sun
  • sunshine
  • Moon
  • Earth
  • Lunar orbit - The Moon completes an orbit - in an elliptical orbit - around the Earth in 27.3 days. It takes the same amount of time to complete one orbit as it does to rotate on its axis. Therefore, we always see the same side of the Moon. This is called synchronous rotation.

A lunar eclipse occurs when the Moon passes into the Earth’s shadow. When this happens, the Sun is not visible from the Moon because of the Earth. The phenomenon only occurs at full moon, that is, when the moon is fully illuminated by the Sun, and the Sun, Earth, and Moon are arranged in a straight line.

The lunar eclipse is visible from the entire nighttime hemisphere of the Earth. It may last for up to 107 minutes, but it may take as much as 6 hours for the Moon to pass through the shadow cone of Earth.

Shadow cone

  • sunshine
  • Sun
  • Earth
  • Moon
  • Lunar orbit - The Moon completes an orbit - in an elliptical orbit - around the Earth in 27.3 days. It takes the same amount of time to complete one orbit as it does to rotate on its axis. Therefore, we always see the same side of the Moon. This is called synchronous rotation.
  • penumbra - A portion of sunlight reaches this region.
  • umbra - The region where the Earth blocks all direct sunlight.

The eclipse

  • sunshine
  • Sun
  • Earth
  • Moon
  • Lunar orbit - The Moon completes an orbit - in an elliptical orbit - around the Earth in 27.3 days. It takes the same amount of time to complete one orbit as it does to rotate on its axis. Therefore, we always see the same side of the Moon. This is called synchronous rotation.
  • penumbra - A portion of sunlight reaches this region.
  • umbra - The region where the Earth blocks all direct sunlight.

Animation

  • sunshine
  • Moon
  • Sun
  • Earth
  • Lunar orbit - The Moon completes an orbit - in an elliptical orbit - around the Earth in 27.3 days. It takes the same amount of time to complete one orbit as it does to rotate on its axis. Therefore, we always see the same side of the Moon. This is called synchronous rotation.
  • penumbra - A portion of sunlight reaches this region.
  • umbra - The region where the Earth blocks all direct sunlight.
  • orbital plane of the Moon
  • orbital plane of the Earth
  • - The angle between the orbital planes of the Moon and the Earth.

Orbital planes

  • Earth
  • Moon
  • orbital plane of the Moon
  • orbital plane of the Earth
  • - The angle between the orbital planes of the Moon and the Earth.

Narration

A lunar eclipse occurs when the Moon passes into the Earth’s shadow. For a thorough understanding of the phenomenon we need to clarify the positions of the Moon and Earth relative to each other.

The Moon is the Earth’s companion and its sole natural satellite. It orbits the Earth, more exactly, it revolves in an elliptical orbit around the common centre of mass of the Moon and Earth. The centre of mass of the Earth-Moon system lies inside the Earth. The moon completes one orbit in 27.3 days. It takes the same amount of time to complete one orbit as it does to rotate on its axis. Therefore, we always see the same side of the Moon. This is called synchronous rotation.

The Moon has no light of its own, but it reflects the light of the Sun. The Earth blocks the sunlight, thus a shadow is formed behind it. Since the Sun is larger than the Earth, the shadow of the Earth is composed of two cone-shaped components. The inner cone, or umbra, is a region of complete shadow which receives no direct sunlight. In contrast, the external part of the Earth's shadow is a region where sunlight is only partially blocked. This part is called the penumbra.

A lunar eclipse occurs when the shadow of the Earth falls on the Moon. Two conditions must be met for a lunar eclipse. First, the Moon must be on the opposite side of the Earth from the Sun, that is, it must be in the Full Moon phase. This is the only way it can be in the shadow cone. The second condition is that the Moon must be located on or near the Earth's orbital plane. Because the Moon's orbital plane is tilted by 5 degrees with respect to the Earth's orbital plane, i.e. to the ecliptic, full moon phases usually occur when the Moon is above or below the Earth's shadow. This explains why lunar eclipses do not occur every full moon, but only two-three times a year.

A total lunar eclipse occurs when the entire Moon passes through the Earth's umbra. A partial lunar eclipse occurs when only a portion of the Moon passes through the Earth's umbra. The third type of lunar eclipse, known as a penumbral lunar eclipse, occurs when the Moon passes through the Earth's penumbra, although this is more difficult to observe with the naked eye. Both total and partial lunar eclipses can be observed from the entire nighttime hemisphere of the Earth. The spectacle can last up to 107 minutes. It can take up to six hours between the moment the Moon passes into the Earth’s shadow until it leaves.

It is not even during a total lunar eclipse that the Moon disappears completely from the night sky; it usually appears to be a deep red colour. This is because the Earth's atmosphere refracts the sunlight, and reflects part of it into the Earth's shadow. Since the long-wavelength red light is less absorbed in the atmosphere, the moon appears red. The colour of the moon and the degree of its darkening depend on atmospheric conditions, but sometimes also on the dust content of the atmosphere.

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