Images credit & copyright: Dan LaShomb (me). Check below for more links and information to figure out your viewing times.
Head’s up! This Friday, July 27, 2018, the Earth will pass directly between the Sun and Moon, creating the longest total lunar eclipse of the century where totality will last 103 minutes (1h 43m). I want to be clear fright from the beginning that this eclipse will not be visible from the Americas, much of Eastern Asia, Greenland or Iceland. It will however, be visible from most of Europe, All of Africa, Australia, the Middle East and most of Asia (especially Western Asia). That same night, Mars will reach opposition and will reside in the same constellation (Capricornus) as the Moon so you may get a special treat of two reddish lights close together on your night sky.
Here’s my post on the July 27 Mars opposition: https://danspace77.com/2018/07/11/now-is-the-time-to-observe-mars/
What is a lunar eclipse?
Typically there are two lunar and two solar eclipses every year to varying degrees. Sometimes it’s a partial and sometimes it’s a total with the Sun having a couple more possibilities like the annular and hybrid eclipses in there as well. When one happens, the other will take place two weeks later. Unlike a solar eclipse where the Moon passes between the Sun and the Earth, casting the Moon’s shadow upon us, a lunar eclipse is where the Earth passes between the Sun and the Moon, casting the Earth’s shadow upon the Moon.
The shadow of the Earth has a couple different conical regions that extend from the earth outward and are set up in a target-like fashion. It has the outer shadow cone; the penumbra and the inner shadow cone; the umbra. When the Moon wanders into the Penumbra (outer region) somewhere on the Earth will witness a partial lunar eclipse. If all the Moon does is enter and exit through the penumbra, the entire event will just be a partial lunar eclipse. However if the Moon’s path takes it through the center of Earth’s shadow it will encounter the umbra and thus somewhere on Earth will witness a total lunar eclipse. A total lunar eclipse always starts and ends with a partial eclipse.
Not anywhere near as dramatic as a total solar eclipse, the total lunar eclipse has some benefits of its own. Where a total solar eclipse can only be seen along a relatively narrow path called the “Path of Totality,” a total lunar eclipse is usually witnessed by half the planet. Also a total solar eclipse’s totality lasts only a few minutes while a lunar eclipse’s totality can last more than two hours.
Why will this total lunar eclipse’s totality last so long?
There are a few basic yet very important reasons why this totality will last 103 minutes (1h 43m) but even though they’re pretty basic reasons, they’re not something you’d think of unless you have a clear understanding of how the process works. The first reason is that when the Earth is further away from the Sun, the umbral shadow or umbral cone (where totality exists) expands. As we reach aphelion (Earth’s furthest point from the Sun in its orbit) during the first week of July every year (July 6th this year) so the umbral cone is slightly larger. In short, the area where totality exists is larger this time, thus the Moon takes more time to travel through it.
Second, if you look at the Sky and Telescope illustration showing the Moon’s path through the shadow you will see that it passes almost directly through the center of the shadow. If it were slightly high or low it would enter totality later and exit earlier but because of the direct pass through, totality will last slightly longer.
The final reason that we have an extended totality this time is because this full moon is a micromoon. That’s right, the opposite of a supermoon. The Moon reaches apogee (its furthest point from Earth in its orbit) also on Friday, July 27 and the further away the Moon is from Earth, the slower it goes.
Take that trifecta into consideration and what you have is a recipe for a long, beautiful red total lunar eclipse. If you’re in the viewing zone, do your best to get out there and have a look. Clear skies!
My 2018 eclipse page: https://danspace77.com/2018-eclipse-schedule/
Time and Date (use the bar about half way down on the right to find your specific times): https://www.timeanddate.com/eclipse/lunar/2018-july-27
Sky & Telescope page for this event: https://www.skyandtelescope.com/observing/red-moon-meets-red-planet-for-lunar-eclipse/
Dominic Ford’s “In The Sky” page for this event: https://in-the-sky.org/news.php?id=20180727_09_100
Fred Espenak’s “EclipseWise” page for this event: http://eclipsewise.com/lunar/LEprime/2001-2100/LE2018Jul27Tprime.html
Apogee & Perigee Calculator: https://www.fourmilab.ch/earthview/pacalc.html
The Danjon Scale of Lunar Eclipse Color: https://perfectastronomy.com/danjon-scale/