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Course: NASA > Unit 2
Lesson 1: Modeling the solar systemTypes of lunar eclipses
Lunar eclipse
The heliocentric model contains one remnant from the geocentric model. Can you find it?
The geocentric model correctly assumed that the moon orbits the earth. We now know this is the reason for the phases of the moon. Why is this? First let's take a look at a sequence of photos taken of the moon over 29 days:
The following is a detailed animation that covers an entire year of the earth/moon cycle. In the center there is a large image of the moon as seen from earth each evening. Take this time to convince yourself why the moon has phases:
Notice that the moon passes directly through the shadow of the earth on days when there is a full moon. Only when the the sun, moon and earth are closely aligned like this is it possible to observe a lunar eclipse. Several cultures have myths related to lunar eclipses. The Egyptians saw the eclipse as a pig swallowing the moon other cultures view the eclipse as the moon being swallowed by other animals, such as a jaguar in Mayan tradition, or a three legged toad in China.
However, the lunar orbit is not perfectly aligned with the earths orbit. It’s shifted by around 5 degrees. This means the moon does not always pass exactly through the middle of the Earth’s shadow, causing the eclipse time to be much shorter. In some cases the eclipse doesn’t occur at all as the Moon sweeps outside the shadow cone.
Variations on an eclipse
Astronomers classify eclipses into three types depending on the position of the Moon around the Earth’s two shadows: umbral and penumbral:
Total lunar eclipse
This occurs when the entire moon passes through the earth’s umbral shadow. This video follows the moon during a total eclipse:
Partial eclipse
This occurs when the moon passes through the earth’s penumbral shadow but only a portion of the much darker umbral shadow.
Penumbral eclipse
In some cases the moon only passes through the penumbral shadow of the earth, these are much harder to observe as there is little change in illumination. Look closely as this is one of the most subtle phenomena in naked eye astronomy:
Challenge questions
Could the length of an eclipse tell us something about the size of the Moon relative to the Earth?
We have 12 full moons per year, how come we always have far fewer lunar eclipses?
Next, we have an interactive simulation which will allow you to explore these lunar eclipses in more detail.
Want to join the conversation?
have anyone heard of blue moon? if yes,then what is it?(10 votes)
A blue moon is when the full moon appears twice in a single solar calendar month. Basically, if a full moon appears twice in one month, such as if Febuary had two full moons, then it is called a blue moon.(15 votes)
With the second picture, does the moon really move in a bit of a circle on the bottom?(5 votes)
It's just two pictures in a GIF. The second picture is taken from a VERY slightly different angle, so it looks like the moon is shaking.(2 votes)
The title is "Types of eclipses" but, they only talk about "Lunar Eclipses" not "Solar Eclipses"
Why??(5 votes)
I think they meant “types of lunar eclipses”(2 votes)
Does it matter if the season changes?( earth's tilting)?(4 votes)
Can you name the eight phases of the moon?(4 votes)
new moon, waxing crescent, first quarter, waxing gibbous, full moon, wanning gibbous, last or third quarter, wanning crescent, then it returns to new moon.(3 votes)
why isn't there a solar and lunar eclipse each month.(3 votes)
for the Lunar eclipse:
The Moon's orbit around the Earth isn't in the same plane as the Earth's around the Sun , this is why we don't have monthly lunar eclipses.
For the Solar eclipse:
it is the exact same reason as the lunar eclipse.
It is good to know that the moon is 400 times closer to the earth than it is to sun, and since the moon is 400 times smaller than the sun, we have total solar eclipses.
This why we are the only planet who witnesses total solar eclipses.
furthermore, the moon is slowly getting farther and farther away from the earth, and this will result in the disappearance of total solar eclipses in the future!(3 votes)
- what is a lunar eclipse?(2 votes)
the time when the earth is between the sun and the moon(6 votes)
- when is the next red moon in 2017(3 votes)
If the solar system were geocentric, how would the eclipses differ?(3 votes)
Even if the solar system was geocentric, eclipses would still be formed by the shadows of the earth and moon. Since the sun would revolve around the earth every day, and the moon would revolve every month (or to be exact, 28 days), the eclipses would also have the same timing. So they actually wouldn't change at all.(3 votes)
Does the moon have to be full in order to have an eclipse?(2 votes)- On the day of Jesus's crucifixion there was a " blood moon " ( lunar eclipse ) and the sun was dark for three hours. How can that be? There is a plausible answer(2 votes)
