Lunar Eclipse Anyone? Try January 31, 2018!
On January 31, 2018, the Moon is doing what it always does, wandering through its orbit of the Earth.
There are a couple of coincidental occurrences that make this particular time, in this particular orbit, a bit special. They all relate to the position of the Earth, Moon and Sun.
Honestly, the Earth Moon and Sun don’t care. They are inanimate celestial objects that obey the laws of physics and don’t have a thinking brain. But to those of us with a thinking brain, and who like to observe the Moon, these coincidences make it a pretty special day. We get to see:
- Full Moon Perigee Syzygy.
- Total Lunar Eclipse.
- Blood Moon.
The Moon is Full.
A full Moon occurs when the Sun and Moon are at opposite sides of the Earth. This happens about once a month. Actually every 29.5 days on average.
This is an exact time. The Moon appears full to us for a day or so. The precise time of Full Moon is UT 13:27 January 31, 2018.
The Moon is at Perigee.
The Moon has an eliptical orbit around the Earth. This means that sometimes it is closer to Earth at other times. When it is close we call that a perigee. When it is at its farthest point we call that an apogee.
Perigee happens once per orbit, every 27 days.
The Moon will enter the Earth’s shadow.
When the light of the Sun hits the Earth there is a shadow extending in the direction away from the sun. Sometimes the Moon passes through this shadow. When the shadow falls on the Moon we call that a Lunar Eclipse.
Here is a diagram that shows how it works:
Image: Public Domain
See the Umbra and Penumbra? These parts of the Earth's shadow occur because the sun is big, and relatively close. The light from the edges of the sun create different levels of light in the shadow the Earth casts out into space.
This Lunar Eclipse is visible as a Total Lunar Eclipse for a good part of Asia and Most of Australia and New Zealand. Other areas see a Partial Eclipse, which means that some of the Earth’s Umbra covers the Moon, or a Penumbral Eclipse, which means that the Moon is entirely within the Earths Penumbra. Penumbral Eclipses are difficult to see as the difference in luminosity is hard to recognise.
Lunar Eclipses are visible from Earth 2–4 times a year.
When three objects are lined up in this way, we call it a syzygy. On January 31, we have a Sun Earth Moon syzygy.
This is the name early astronomers gave to a Lunar Eclipse. The reason is that the Full Moon looks red from Earth during an eclipse. I imagine that must have been terrifying for people without astronomy to teach them why.
During a total Lunar Eclipse there is no light directly from the Sun to reflect back at us. The only light reaching the surface of the Moon has been refracted by the Earth’s atmosphere around the Earth. The Earth’s atmosphere scatters blue light, that makes our sky blue, and the remaining light has a red tint. This light makes the Moon appear red.
When a Full Moon coincides with a Perigee it is commonly known as a Super Moon. It appears up to 14% bigger and 30% brighter than a normal Full Moon.
SuperMoon is an astrology term. We do science here, so we’ll call it a perigee syzygy. It’s also way more fun to say out loud.
January 31, 2018
- We have the Moon at Perigee.
- We have the Moon at full phase.
- We have the Moon entering the Earths shadow for a Lunar Eclipse.
- Full Moon Perigee Syzygy.
WOW! How can I see it?
This diagram will tell you if you can see it from where you are.
Image: By PIRULITON (Own work) [CC BY-SA 3.0 (Creative Commons - Attribution-ShareAlike 3.0 Unported - CC BY-SA 3.0)], via Wikimedia Commons
If you are in any of the area that can see some or all of the Lunar Eclipse, all you have to do is go outside after sunset and look up at the Moon. A Lunar Eclipse takes quite a bit of time (unlike a Solar Eclipse), so plan to watch at the times that something is happening.
Watch the shadows change though. This page gives you the times. January 2018 lunar eclipse - Wikipedia
If you are not in the area of visibility, there will be plenty of streaming and photo sharing. The Internet makes everything accessible.
Blood Moon Feature Image: By George Navro (Own work) [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons
Adapted from article first published on Quora.