Total Lunar Eclipse Coming This Sunday Night

We’ll see a big, orange moon Sunday night (Jan. 20) when Earth’s shadow totally eclipses the Full Wolf Moon. Bob King

You won’t want to miss Sunday night’s total lunar eclipse. If you do, the next one won’t be till May 26, 2021. The eclipse takes place between about 9:10 p.m. (Central Time), when we’ll see the first hint of the Earth’s outer shadow darken the moon’s edge, until 1:15 the next morning, when the moon breaks its alignment with the sun and Earth and eases back into sunlight.

Lunar eclipses — penumbral, partial and total — always occur at full moon, when the moon, earth and sun line up squarely in a row in that order. Only then does the Moon pass through the shadow cast by our planet. Starry Night with additions by the author

A lunar eclipse can only occur during a full moon because full moons are always directly opposite the sun. From outer space, we’d see the sun, Earth and moon in that order. Earth casts a two-part shadow — a dark core called the umbra surrounded by the lighter penumbra. The penumbra isn’t fully dark because sunlight filters into it, diluting the darkness. From the viewpoint of someone standing on the moon looking back, the Earth has only covered part of the sun. The moonscape is twilight-like but not yet dark.

This diagram shows the key phases during the upcoming eclipse as he moon passes into and out of Earth’s shadow. Times are CST. See the table at the end of the blog for eclipse details for other time zones. Fred Espenak, NASA’s GSFC with additions by the author

During a lunar eclipse, the moon passes first through the penumbra and then into the much darker umbra. The umbra is only about 1.5° wide or the width of your thumb held at arm’s length toward the sky. For the moon to pass through that small target, the lineup has to be nearly exact. The “black bullseye” is always there, but because the moon’s orbit is tipped 5.1° to Earth’s orbit, most full moons miss it, passing a couple degrees above or below the shadow.

By the way, Sunday’s full moon will be a little larger than normal because it happens to be undergoing eclipse just one day before its closest approach to the Earth called perigee. That makes a supermoon, the first of three in 2019. Will it look bigger to your eyes? Probably not unless you’ve really been paying close attention to the moon’s size during recent full moons. The average apparent diameter of the moon is 31 arc minutes or just a hair more than a half-degree. That’s half the width of your little finger held at arm’s length. Sunday’s supermoon will be 2.2 arcminutes or 7 percent larger. Let us know if you can tell.

January’s total lunar eclipse is observable from North and South America, Europe, Northwest Africa, and the Arctic. It will be primarily an evening event for the Americas and a morning one for Europe and Africa. The star over Cuba marks the spot where the totality eclipsed moon will shine from directly overhead. Fred Espenak, NASA’s GFSC

Unlike a solar eclipse where you have to take precautions to shield your eyes against the sun, you can watch every part of a lunar eclipse. You don’t even need equipment to enjoy the view, but bringing binoculars along doesn’t hurt. They enhance the eclipse colors and show stars shining right next to the full moon during totality —  a beautiful sight only seen during an eclipse. Telescope users can track the shadow more closely and watch it cover the larger craters and lunar seas like a spilled tea slowly soaking into paper.

Times for the eclipse across the four main U.S. time zones.

You’ll first notice the penumbral shading around 9:10 p.m. (CST) or even a little earlier. It’s not a “hard bite” like the umbra makes but more of a dusky shading along the left-hand (celestial east) side of the moon. 25 minutes later, the moon eases into the umbra for that first nibble of shadow. As it progresses deeper into the gloom, look for the first signs of color, usually orange or red. Two things about the shadow — it’s curved and it’s fuzzy. I bet you can guess why it’s curved. If you said because the Earth is spherical and spherical objects cast curved shadows, give yourself 10 bonus points.

 

From the moon on Sunday, an observer would look back to see a total solar eclipse with Earth ringed by its reddened atmosphere set against the pearly solar corona. Stellarium with additions by the author

Earth’s shadow has a fuzzy edge for the same reason a tree casts a fuzzy shadow. Because the Sun is an extended disk rather than a point of light, light from one side of the disk spills into areas that the other side of the Sun can’t reach and vice versa. This “spillage” softens and diffuses the shadow’s edge. Only point sources like Venus can create sharp-edged shadows.

Once the moon is fully engulfed in shadow and totality has begun, the lunar disk is awash in yellows, oranges and reds. This sight of the moon painted in vivid colors is often the highlight of the eclipse. It looks almost alien up there among the stars. If you’re lucky enough to live where light pollution is low, you’ll see all the stars and Milky Way return for an hour when the moon is inside the umbra. A totally amazing transformation!

I put a bunch of photos together from the April 14, 2014 eclipse to make a collage showing the partial phases and totality. Bob King

If the Earth had no atmosphere the moon would be utterly black once fully within Earth’s shadow. But our atmosphere bends the light of the sun — located in front of the Earth, remember? — and focuses it inside the shadow. Because the light grazes the edge of the planet exactly the same way it does at sunrise and sunset, those are the colors that light up the moon! To gaze at the eclipsed moon is to see the light of every sunrise and sunset around Earth’s 360° perimeter. That’s what I call poetry.

If the moon is relatively bright in Earth’s shadow, it’s a sign our planet’s atmosphere is relatively dust-free. But if large volcanoes have been recently active, filling the atmosphere with ash and sulfur dioxide, the moon can appear unusually dark. Because the moon in this eclipse travels north of umbra’s center, its top half will probably appear brighter than the bottom.

During totality the moon will have company. Look for M44, the Beehive Cluster, about 6° east of the Moon with either the naked eye or better, binoculars. Stellarium

As the moon continues through the shadow traveling at an average speed of 2,288 mph (3,682 km/hour), it soon gets to the other side of the umbra and slowly emerges into the “partly sunny” penumbra again, signaling the end of totality. Another hour or so passes before it leaves the umbra.

The last lunar eclipse happened just shy of a year ago during the early morning hours of Jan. 31, 2018. I’d argue that this one will be a little easier to watch because it occurs during convenient evening viewing hours. Some of you will catch the entire eclipse, but if you’re short on time and just want the juicy parts, be out from 10:15 p.m. to 10:45 p.m. (CST) to watch the end of the partial phases and beginning of the totality. For the Eastern Time Zone, that would be 11:15-45 p.m.; Mountain 9:15-45 p.m. and Pacific 8:15-45 p.m.

Lots of us will be taking photos. That’s why I recommend Fred Espenak’s Mr. Eclipse site for everything you need to know. If you are using mobile phone, be aware that the moon will be very small in a black sky in your photos. I recommend waiting until shortly before, during and after totality to take pictures. At those times, the ambient city light will be a better match for the moon, which will allow you to frame the moon with a night scene. Be sure you bring something to steady your phone like a bean bag, otherwise it will shake during the exposure, blurring everything.

Good luck and clear skies!

10 Responses

  1. Troy

    The only thing regrettable about Change’e 4 landing on the lunar far side is that it would have a great platform to watch the eclipsed Earth with its red halo. (I’m pretty sure the other Chinese landers are no longer functional otherwise they could take it in)

  2. kevan hubbard

    I was looking forward to it and had planned on going out into the fields with my very unusual pocket Borg 25mm refractor,said to be the smallest astronomical telescope made(things like the 5×10 Zeiss mini quick monocular which I also own being mainly designed for land use although it gives a fair view of the Moon) and a collection of eye pieces.sadly I have an hospital appointment now at 1120 and staying up all night won’t be ideal!still I will see how I feel or better still,for me!,it’ll be cloudy and I won’t feel cheated!?

    1. astrobob

      Kevan,
      Good thing is, the eclipse lasts so long, you’re almost sure to see part of it as long as you’re not clouded out.Good luck!

  3. Sheila

    Where in the sky will the moon be when the eclipse happens? Which direction should I look? Hoping to find a window that we can see it out of at work tonight.

    1. astrobob

      Sheila, the eclipse happens SUNDAY night, just so you’re sure on your days. The direction depends on what part of the country you live in. Tell me your state and about what time you’ll be looking.

      1. Sheila

        SUNDAY night. ok. got it! Duluth MN. Working afternoon shift at the hospital.
        Hoping to sneak a glance or two out the window during my shift and catch the end of it outside after work.

        1. astrobob

          Sheila,
          The moon will way up over the lake at the start of the eclipse around 9:35 p.m. and will just keep getting higher after that. So just find a place where you can look toward Wisconsin over L. Superior.

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