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Who doesn’t love a lunar eclipse! While not as spectacular as their solar counterparts, a total lunar eclipse is a beautiful sight at night, and gives the sky more sense of wonder! Unless you are severely unlucky when it comes to weather, or if you just never look at the moon, chances are you will see several, perhaps over a dozen lunar eclipses in your lifetime!

Lunar eclipses are much more commonly seen compared to Solar eclipses, mainly because the entire night side of Earth can observe a lunar eclipse as our moon enters and exits earth’s shadow. If the eclipse happens while you’re on the day side, well then… you get the idea.

Because lunar eclipses are not as hyped or promoted, there have often been nights where people have walked up to me because of the telescope and wondered why I was outside observing, only for me to tell them, “dude, look up! It’s a lunar eclipse!”

What Causes Them

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A Lunar eclipse, or eclipse of the Moon, can only occur during a full moon phase! What is actually happening is that there is a solar eclipse happening from the surface of the moon. From the Moon, the Sun appears to get eclipsed by Earth! Earth just gets a front row seat to watch the effects happening on the moon.

Just like a person or an object casting a shadow on Earth and blocking sunlight, Earth too has a shadow in space!

A lunar eclipse caused by the Moon going inside Earth’s shadow and getting deprived of sunlight.  Because of Rayleigh Scattering, the same mechanisms that give sunrises and sunsets the colorful appearances on Earth, the red and orange light from the Sun gets refracted by Earth’s atmosphere, and gets projected on the face of our moon during lunar eclipses, which is why we often have the “blood moon” appearance. One cool way to think about it is to consider the refracted light is every sunrise and sunset happening on Earth being projected on the Moon!

The Ancient Greeks were the ones who figured out the moon was going behind Earth and entering Earth’s shadow, and because they saw that Earth’s shadow was round, that made them conclude the earth was in fact round and shaped like a sphere!

Sometimes, you will have a sequence of four lunar eclipses happening within a span of two years. This is called a tetrad, and happens every couple of decades or so on average.

What Happens During the Eclipse

There’s two parts of Earth’s shadow. The penumbra is the outer edges, while the umbra is the central shadow.

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Here, the Moon only passes through the penumbra part of Earth’s shadow.

If the moon just crosses through the penumbra, even partially, then you get a penumbral eclipse. Very rarely, the moon crosses fully through the penumbra without touching the umbra. This would be called a total penumbral eclipse. However, as rare as they are, they are not very impressive.

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As you watch the moon cross into the penumbra, you won’t notice too much difference in brightness on the moon’s face. A penumbral eclipse can be happening and people wouldn’t know it. They literally just look like an edge of the moon is being dimmed by a thin cloud.

A partial lunar eclipse will happen once the moon crosses through the outer shadow into the umbra, and then you see what looks like something taking a “bite” out of the moon. Until the moon completely crosses through the umbra part of the shadow, the eclipse is in partial phase. As you see the “bite” get larger, you can start seeing the shadowed portions begin to turn into the familiar red color. Sometimes, the moon doesn’t cross completely into the umbra, so you’re left with just a partial eclipse.

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This was taken at the end ot totality from the last eclipse on 1/31/2018

But when the moon has completely crossed into the umbra, we have a total lunar eclipse! By this time, the entire moon is showcasing the familiar copper or red color. The brightness of the eclipses can vary depending on Earth’s atmosphere. Sometimes the moon is a vibrant orange-red color, other times it’s a deep brick color, and then there are times when the eclipse appears grayish and almost invisible – usually caused by heavy ash in the atmosphere by a major volcanic eruption!

The length of totality can last anywhere from a few minutes to over an hour, depending on how far into the central portion of the shadow the moon passes through. As the moon moves into the umbra, the outer edges get darker. mid eclipse occurs when the moon is closest to the central umbra, where the eclipsed moon shows deeper colors. When you start seeing the outer edge start to brighten up again, that means totality is almost over!

Totality ends when the moon begins leaving the umbra, and you start seeing a bright sliver of bright white start to drown out the red. This will take another hour before the moon exits the shadow completely. By then, the moon’s face has returned to normal.

The next total lunar eclipse visible from North America will be January 20-21, 2019.

Best Ways to View Them
  1. Always check your local times for your observing location.  Websites like timeanddate.com will give you exact times for each phase of the eclipse, from the moment our Moon enters Earth’s penumbra, to when partial eclipse begins, to when totality begins. If anything, these sites will tell you if your location will even see the eclipse at all.
  2. Depending on the exact time our moon enters Earth’s shadow, the eclipse from start to finish will happen at different times based on your location. Some places will see the eclipse happen at convenient times, others will see the eclipse during the middle of the night.
  3. You do not need any special equipment to view the eclipse either! They are beautiful sights with the naked eye, and are visible for a few hours.
  4. It’s not uncommon for people to make multiple trips outside from the comforts of their home to see the eclipse phases change with every brief glimpse. Only true dedicated watchers are outside during the entire eclipse.
  5. Through binoculars or a telescope, it’s best to view at low power so the entire lunar disc is visible in your field of view. Zooming in only shows the shadow gradually move across a smaller portion of the lunar surface, and at high magnification you won’t see too many details.
  6. The moon’s brightness will keep changing, so if you want to take pictures of it, you need to adapt to different exposures on your camera to get the best pictures.
  7. If there is cloudy weather, don’t worry! Chances are there will be another lunar eclipse visible from your location within 1-2 years!
  8. You don’t need any special protection for your eyes to view the event. All you need to do is dress appropriately, as you may be outside at night for a long period of time.
  9. If you have seen totality end and the Moon start returning to normal, it’s perfectly acceptable to stop watching, as the eclipse is now in the anti-climatic phase, and typically only those who are taking pictures or filming time lapses will view the eclipse to the very end.

 

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