The Best Total Lunar Eclipses Visible From the US Between 1990-2060

Specifics for the May 15/16, 2022 Total Lunar Eclipse: Excellent for all the US

Early Sunday evening May 15, 2022, there will be a lovely total lunar eclipse visible across North America. Here is a nice graphic of the eclipse showing the Earth's shadow and the path of the Moon (from the Espenak NASA website, which has similar graphs for all the eclipses). Here, UT is Universal Time. Subtract 5 hours for CDT, 4 hours for EDT, etc. The partial phase of the eclipse begins at 9:28 pm CDT, with the total phase from 10:29 pm through 11:54 pm CDT, and the partial phase ending at 12:55 am CDT. During the partial phase it will look as if a bite has been taken out of the Moon. During the total phase, the Moon will have a dull or bright red color, depending on how red the Earth's atmosphere appears for an observer located on the surface of the Moon. This eclipse ranks as one of the best ones we can see.

The pre-dawn Total Lunar Eclipse of November 8, 2022, nice for photography

The second total lunar eclipse visible of 2022 from the US will occur in the early morning hours of Tuesday November 8. Like the one earlier in May, this one is a nice long eclipse, also with 85 minutes of totality. In fact, the difference in totality length is only 5 seconds from the May eclipse. It's rare to have subsequent lunar eclipses have such nearly identical durations. The next time that happens to this level of precision will be in 2091, and then not again until 2998. Unlike the supermoon May eclipse the Moon is a little smaller than its normal size for this eclipse. The partial phase begins at 4:09 am CDT (are we still doing daylight time? Congress?), and the total phase goes from 5:16 am to 6:42 am CDT. The Moon emerges fully from the darkest shadow at 7:49 am, about the time that the Sun rises in the middle of the country. On the east coast, the Moon will set just as the total eclipse is ending. This eclipse will have some nice possibilities for photography, as the Moon will be low in the west for many during and around totality. It should be possible to frame the Moon against a backdrop of a landscape or a city skyline with a bit of preparation beforehand.

So which total eclipses are the best ones in the next several decades?

It seems to me for an eclipse to be a good one for US viewers it needs to be (in order of preference)

  • Visible from the US
  • Total (eliminate partials and penumbrals)
  • Central eclipse occurs at a convenient time of the evening
  • Have a long total phase
  • Have the Moon be close so it looks bigger (if we can get that, why not?)

    Let's look at some plots. First, of the total lunar eclipses visible from the US between 1990 and 2060, which ones have a long total phase and are at a convenient time in the evening:

    So the May 15-16, 2022 eclipse does quite well for itself:

  • It is visible in the early evening from the US
  • It has a good duration of about 85 minutes.
    The big triangles denote a supermoon, when the Moon appears somewhat larger than normal because it is closer to us than average. Supermoons are not rare, in fact about 1/4 of all full Moons are supermoons, and there is no discernible size difference between different supermoons. Here is a plot of the size of the totally-eclipsed Moons visible from the US during the 1990-2060 interval, with the red triangles being supermoons:

  • So the May 15-16, 2022 eclipse is a supermoon.
    The next total eclipse that satisfies all these criteria isn't until Oct 30, 2050! Of course, if we relax the supermoon constraint and just look for total lunar eclipses visible from the US that are of a reasonable duration and occur at a convenient time, we have:

    Convenient (early evening for USA) Total Lunar Eclipses out to 2060
    May 16, 2022Supermoon
    Mar 14, 2025
    Jun 26, 2029
    Aug 7, 2036
    Sep 19, 2043
    Jan 12, 2047
    Jan 1, 2048
    Oct 30, 2050Supermoon
    Apr 26, 2051
    Feb 22, 2054Supermoon
    Nov 30, 2058

    The dates listed for eclipses are UT, and therefore refer to the date after midnight for the night in question for the US. That is, the eclipse at 10pm on the evening of Jan 20, 2019 is labeled as '1/21/19', while the eclipse at 3 am on August 18, 2054 is labeled as '8/18/54'. Here I have defined normal to be 379000 km, equal to the semimajor axis of the Moon's orbit minus about 4000 km to compensate for a typical position on the Earth that sees the full Moon.

    It is interesting that there is a bit of a gap in the supermoon eclipses after 2022. In part this is caused by these eclipses being visible on the other half of the globe. We can see this in the following plot of the sizes of all full Moons between 2010 and 2040, where total eclipses are red dots, and partials have red X's (skip the penumbrals, which are pretty lame, the Moon barely gets dark in those). Triangles and asterisks highlight eclipses visible from the US:

    Sure enough, you can see there tend to be more red dots without triangles between 2025 and 2040. These will be total eclipses visible on the other half of the globe, e.g., India.

    Some general questions and answers that relate to lunar eclipses (more complicated stuff at the end):

    What is a lunar eclipse?
    A lunar eclipse occurs when the Moon travels through the Earth's shadow.

    What is a blood Moon?
    No astronomer I know uses this term (at least not when we are talking with each other), as it sounds more at home in a vampire novel. Usually it simply refers to an eclipsed Moon, which appears red because sunlight from all the sunrises and sunsets on Earth are simultaneously visible on the lunar surface. It is a poor description because few fully-eclipsed Moons appear blood-red. Most are a reddish-brown color. Some are grey or even black, and a few are copper-colored.

    What is a Supermoon?
    Another item of popular culture. This one refers to a full Moon that occurs when the Moon is near perigee, it's closest approach to the Earth (see my article on supermoons).

    Are there different types of lunar eclipses?
    Yes. The Earth's shadow has an 'umbra' and a 'penumbra'. If you are in the umbra and look towards the Sun, the Earth blocks the entire Sun. If you are in the penumbra you would see the Earth blocking only part of the Sun. Hence, there are three types of lunar eclipses: (1) Total eclipses where the entire Moon is in the umbra. During these, the only sunlight that reaches the Moon comes from the glow of the light refracted and scattered from the Earth's atmosphere, which would look like a fiery red ring everywhere on the Moon. For this reason the Moon looks reddish during a total eclipse. Most total eclipses last about an hour or so. (2) Partial eclipses occur when only part of the Moon is in the umbra. The Moon looks like it has a chunk taken out of it. Partial phases also bracket every total eclipse, each lasting about an hour, typically. (3) Penumbral eclipses occur when the Moon misses the umbra entirely. From the Earth these are subtle to detect, with only a weak dimming on one side of the full Moon. If you were on that part of the Moon, the Earth would only block part of the Sun. Total eclipses are by far the most interesting to observe.

    Why the red/brown color in a total eclipses?
    The Moon is not completely dark during a total eclipse because the Earth's atmosphere bends the Sun's rays around the Earth even when the Moon is in shadow. Mainly the red rays make it through the Earth's atmosphere to the Moon (like what happens at sunset and sunrise), because the blue light is scattered away by molecules in the atmosphere. If you were on the Moon during a total lunar eclipse, the Earth would appear as a dark ball that surrounded by a glowing red halo. Hence, the Moon often appears red during eclipse, though this can vary enormously between eclipses. Some lunar eclipses are very dark owing to volcanic dust if there has been a recent eruption.

    You may want to rank the eclipse on the `Danjon' Scale of brightness. Here is that scale; the term `umbra' refers to the dark part of the Earth's shadow.

    L-value   Description
    0  Very dark eclipse. Moon almost invisible,
       especially at mid-totality.
    1  Dark eclipse, gray or brownish coloration;
       details distinguishable only with difficulty.
    2  Deep red or rust-colored eclipse, with a
       very dark central part in the umbra and the
       outer rim of the umbra relatively bright.
    3  Brick-red eclipse, usually with a bright or
       yellow rim to the umbra.
    4  Very bright copper-red or orange eclipse,
       with a bluish, very bright umbral rim

    How frequent are all lunar eclipses and total eclipses?
    We usually get two or three, including all types, each year. On average we get about one total lunar eclipse every year, but sometimes we'll get two in a year and sometimes none. Since total eclipses are only visible from the side of the Earth that happens to be facing the Moon at the time, any given location on the Earth will be able to see a total lunar eclipse about once every 2-3 years. Including penumbral eclipses, which just make a corner of the Moon a bit dimmer, you can get as many as five lunar eclipses in a year, though that's pretty rare.

    Why doesn't this occur every month as the Moon orbits the Earth?
    The Moon's orbit is tilted about 5 degrees relative to the Earth's orbit around the Sun. So usually the Moon either misses the shadow above or below as it orbits the Earth. To line up the Sun, Earth and Moon well enough to get the Moon into the Earth's shadow you have to have the Moon lie nearly in the plane of the Earth's orbit around the Sun when the Moon is full. The points where the Moon crosses the plane of the Earth's orbit are called nodes. Lunar nodes are aligned with the Sun and Earth every 6 months, and during that time we get eclipses. For example, in 2022, the eclipse seasons are May and November.

    What is a tetrad?
    This is when four successive lunar eclipses are all total ones, without any partials or penumbrals interspersed. Typically the total eclipses will not all be visible from the same location, as the Moon will be below the horizon for some of the four.

    Do eclipse seasons change?
    Yes. For example, in 2017 the lunar and solar eclipses occurred in February and August, and by 2019 they've shifted to January and July. Eclipses occur a little earlier each year, and return to their original starting point after about 18.6 years. This `regression of the nodes' is caused by the lunar orbit wobbling like a top around the Earth in response to the torques acting on it by the bulge of the Earth and the pull of the Sun, both of which are inclined to the lunar orbital plane.

    Does the fact that perigee occurs during eclipse make an eclipse special?
    It does makes it very unusual. It occurred during the September 2015 eclipse, and will again on Oct 8, 2033 (one saros period in the future). In terms of how the eclipse appears though, a supermoon eclipse is not going to look a whole lot different from a typical eclipse because the amount of the increased apparent size of the Moon at perigee is rather minimal.

    Distances and Orbital Shapes:
    Interestingly, even though perigee occurs during the 9/27-28/15 eclipse, and perigee occurs 14 hours after the eclipse on 1/20-21/19, the eclipse on 1/20-21/19 is the closer of the two. How can this be? The main factor here is that the 1/20-21/19 eclipse occurs around midnight for US observers. At midnight the full Moon is highest in the sky, and the observer is closest to the Moon than during other hours of the night. The 9/27/15 eclipse occurred in the early evening for US observers and so was at a slightly larger distance than if the eclipse were to occur at mignight (the Earth's radius is about 6400 km, about 2% of the distance to the Moon, so the effect of different locations on the lunar distance is typically about 1%).

    There is another more interesting effect on the distances that has to do with the lunar orbit. The eccentricity of the lunar orbit is never higher than about 0.078, so the maximum variation in the apparent lunar diameter is never more than about 15%, and can be as low as 5% at times when the orbit is most circular. This difference in size is noticeable, but not dramatic. The lunar eccentricity has many periodic variations, and gets most eccentric when the major axis of the Moon's elliptical orbit aligns with the Sun. Have a look at the instantaneous eccentricity (part of what is known as the osculating elements of the orbit) of the lunar orbit from Figure 4.6, again from the excellent NASA site.

    According to this lunar calculator, the 1/20-21/19 perigee is slightly farther away (357344 km) than the 9/27-28/15 perigee (356876 km). This difference occurs because the perigee time did not align as well with the full Moon on 1/20-21/19 as it did on 9/27-28/15. There are closer perigees, for example on Nov 14 2016 (356511 km; angular size 34.1 arcminutes when viewed from the optimal location on the Earth, in this case near Hawaii), but no eclipse occurs during that full Moon because the lunar nodes do not align with the Sun during November of that year. The absolutely closest perigees occur when they coincide with the full Moon, and occur in early January when the Earth is closest to the Sun. All this is discussed in my supermoon article.

    In celestial mechanics one can describe the lunar motion in terms of a stable orbit that undergoes a perturbation by a third body (either the Sun or the bulge of the Earth). The equations of motion are then reformulated in terms of a perturbation function. The orbit is described by 6 parameters, two for shape (a = semi-major axis, and e = eccentricity), three for the orientation of the ellipse in space (i = inclination, node = location of node, and omega = location of perigee), and one to place the object on the orbit (tau = time of closest approach). One can solve the perturbation equations for each orbital parameter and determine secular, short-term-periodic, and long-term-periodic components to the equations. The NASA graph shows that these perturbations generate periodic changes in the eccentricity, with rather intricate variations with time. The Moon's orbit is quite tricky to get right!

    Fun fact: The eclipse on Jan 1, 2048 is actually ongoing at midnight. So on that date we can ring in the new year with a total eclipse of the Moon!

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    Patrick Hartigan