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Eclipse Review
I watched from a beautiful nature reserve in central Missouri, and it was--without exaggeration--the coolest thing I've ever seen.
Title text: I watched from a beautiful nature reserve in central Missouri, and it was--without exaggeration--the coolest thing I've ever seen.

Explanation

Ambox notice.png This explanation may be incomplete or incorrect: First draft - Additions to this would be useful, alter this tag if you alter the explanation

This comic is the fifth consecutive comic with a solar eclipse as the topic. On August 21, 2017, a total solar eclipse was visible within a band across the contiguous United States from west to east. The other comics are 1876: Eclipse Searches, 1877: Eclipse Science, 1878: Earth Orbital Diagram and 1879: Eclipse Birds. As the first XKCD written since the total solar eclipse, Randal is ready to provide his "review."

The comic is another comparison graph, like 1775: Things You Learn or 1701: Speed and Danger. It contrasts how cool something sounds and how cool it actually is. It has five points on it, planetary conjunction, supermoon, lunar eclipse, partial solar eclipse, and total solar eclipse.

While the four other things than total solar eclipse are relatively close to each other on the "how cool to see" scale, the graph is not even high enough to plot the total solar eclipse point as indicated by the dotted arrow showing that this point should be way higher up. This is as opposed to leaving the point out, as Randall did with the coconut in 388: Fuck Grapefruit, where it is only mentioned in the title text. This could be an indication that if the scale had been high enough to fit the total solar eclipse point, then the rest of the points would be on the x-axis without any indication of which would be cooler.

A total solar eclipse correctly sounds like it is the coolest of the five, but it is vastly cooler to see it in person by a wide margin. It seems like Randall is trying to convice those who missed the eclipse this time to go watch in seven years when another total solar eclipse is visible in the USA.

Planetary Conjunction

In a planetary conjunction two or more planets are visible in night sky nearby. This happens relatively often because all planets roughly lie in the same plane around the sun (the Sagittal ecliptic). This looks like two big stars close to each other, and isn't particularly exciting.

Supermoon

A supermoon is a full moon or a new moon that approximately coincides with the closest distance of the Moon on in its elliptic orbit around the Earth. This results in a larger-than-usual apparent size of the lunar disk, but a typical human doesn't recognize the difference. Nevertheless in the last years the press always announces this as an important astronomical event. The opposite is called a micromoon. A "supermoon" sounds very cool, but like a planetary conjunction it's almost indistinguishable from the average night sky.

Lunar Eclipse

A lunar eclipse can occur at full moon and happens only, like at a solar eclipse, when the Moon is in the region where the orbital planes of the Moon and the Earth intersect. The Earth's shadow falls on the Moon and it appears in dark red because some light still reaches the Moon through the outer layers of the Earth's atmosphere. Lunar eclipses occur more often than solar eclipses and they can be viewed by much more people at the same time in the night sky. Only people on the day-side can't see it. A lunar eclipse looks noticably different from a usual full moon, making it fairly cool.

Partial Solar Eclipse

There are three types of partial solar eclipses. An annular eclipse occurs when the Sun and Moon are exactly in line with the Earth but the Moon is too far away and can not block the entire Sun. The Sun appears as a very bright ring, also called annulus. A partial eclipse occurs when the Sun and Moon are not exactly in line to the observer on Earth and thus the Sun can't be fully blocked by the Moon. A hybrid eclipse is a total and annular eclipse at the same time. At some locations on Earth it appears as a total eclipse, while at other locations it appears as annular. These mixed eclipses are comparatively rare. A large percentage of the continental United States experienced a partial eclipse along with the total solar eclipse on August 21st. A partial solar eclipse is quite cool, but nowhere near as dramatic as a sky-darkening total solar eclipse.

Total Solar Eclipse

The total solar eclipse is the topic of this and the four preceding comics. It can occur at new moon and happens only when Sun and Moon are exactly in line with the Earth. But unlike to the lunar eclipse only a small part of the Earth is in the totality zone, a disc with a diameter of approx. 100 km. The disc moves very fast over the Earth's surface and at a specific location it lasts only a few minutes in maximum. At locations outside of this shadow-disc, in a region over a few thousand kilometers, the eclipse is partial.

In the title text, Randall remarks that, without any exaggeration or hyperbole, the total solar eclipse was the coolest thing he has ever seen in his life.

Transcript

[A scatter plot with five labeled dots is drawn. The x-axis reads "How cool it sounds like it would be" and the y-axis is labeled with "How cool it is to see in person".]
[Bottom left] Planetary conjunction
[Bottom middle] Supermoon
[Low left-center] Lunar eclipse
[Low-center middle] Partial solar eclipse
[Upper right, with a dotted arrow above it pointing up] Total solar eclipse


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