Total Lunar Eclipse

A total lunar eclipse occurs when the Earth is between the Sun and the Moon.  The alignment of the three celestial bodies needs to be close to perfect.

The dark part of the Earth's shadow (Umbra) will full encompass a Full Moon for a total lunar eclipse.  Penumbral eclipses occur when the Moon is only within the penumbra of the Earth's shadow.

Umbra and Penumbra (Image Credit: NASA)

When you see a total lunar eclipse you will notice that the Moon will appear red.  The reason for this is the blue part of the electromagnetic spectrum (visible light) is readily scattered by the Earth's atmosphere.  This leaves the red light to refract onto the Moon.  This is the same reason why a sunrise or sunset will appear to be shades of red and why the sky is blue during the day. 

Here is an easy experiment that you can try at home:

Put some water into a transparent drinking glass.  Next put a very small amount of milk into the same glass just so it is slightly cloudy.  Finally, shine a white flashlight up through the bottom of the glass.  The region of the water/milk mixture further away from the light will appear 'redder' while the region closer to the light will appear 'bluer'.

Total lunar eclipses are certainly not as exciting a total solar eclipse with the latter being considered one of the most amazing celestial visuals.  A total lunar eclipse may last more than an hour and be visible across entire continents.  Whereas a total solar eclipse lasts mere minutes in a relatively small zone of totality.

What will you expect to see during a total lunar eclipse?

1. Penumbral Eclipse - The Moon may appear slightly shaded during the first part of the total eclipse.
2. Partial Eclipse - The umbra of the Earth's shadow will be seen on the Moon and it will start to look like a bite of the Moon has been taken out.  The Moon will slowly start getting more red.
3. Total Eclipse - The Moon will be completely in the umbra and will appear very red.
4. Partial Eclipse - The eclipse will start to cycle out with the umbral bite getting smaller and smaller.
5. Penumbral Eclipse - The Moon will progressively get lighter as the eclipse comes to a close.

When the Moon is completely covered by the Earth's umbra it should look something like the image below.

Total Lunar Eclipse (Image Credit: NASA)

There are two more total lunar eclipses visible from Calgary this decade (2010s).  January 31, 2018 and January 20/21, 2019.

The eclipse on January 31, 2018 is quite interesting as it will occur during the second full Moon of the month.  Due to a publication error in the 1940s when there is a second full Moon in a month it has become colloquially known as a 'Blue Moon'.  The original traditional definition of a 'Blue Moon' is the third full Moon in a season that has four full Moons.

Depending on if you accept the colloquial definition this total eclipse will be a Blue Moon total eclipse.  A lot of memes on social media indicate this is the first time in 150 years.  This is not entirely true.  The last one was late in 1982, just not in the timezone of the Americas.  It is true that the last Blue Moon total eclipse in the American time zone was in 1866, just after the Civil War ended.

Another thing that makes the 2018 eclipse interesting is that the Moon will be close to perigee.  This makes it a Super Moon.

The red colour of the Moon cause people to call it a Blood Moon.

The details for the January 31, 2018 eclipse are below:

3:51am - Penumbral Eclipse Starts
4:48am - Partial Eclipse Starts
5:51am - Total Eclipse Starts
7:07am - Total Eclipse Ends
8:11am - Partial Eclipse Ends
8:18am - Moon sets

The eclipse in 2019 will not be a Blue Moon but will be a Super Moon.  In fact, people are referring to it as a 'Super Blood Wolf Moon'.  The 'Wolf' part coming from the Farmer's Almanac which named Full Moons based on learnings from Native American Tribes in the Great Lakes region.  It is important to note that most tribes have different names for the Moons.

These names are merely constructs to add to the hype of a relatively common event.  You will see them used quite a lot in the media.  Astronomers are content to merely call them Total Lunar Eclipses.  However, I like to use them on occasion to get more people out of their homes to astronomers with telescopes!  The more photons from astronomical events hitting eyes the better!

The details for the January 20/21, 2019 eclipse are below:

7:36pm - Penumbral Eclipse Starts
8:33pm - Partial Eclipse Starts
9:41pm - Total Eclipse Starts
10:43pm - Total Eclipse Ends
11:50pm - Partial Eclipse Ends
12:48am - Penumbral Eclipse Ends

I hope to hear your stories about the eclipses!

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