xkcd.WTF!?

Explanation ➲

There are various different types of solar eclipse. The comic purports to show and name a number of them, initially quite real and accurate before heading into traditional xkcd fantasticality.

Label	Image	Occurs naturally	Description
Partial	Sun partly obscured by an offset occlusion	Yes	When the Moon passes between the Earth and part of the Sun's disk but is not perfectly aligned (for any or all observers), the 'shadow' will not cross the center of the Sun. The parts of a full eclipse before second contact and after third contact are also described as partial phases of the eclipsing event.
Total	Sun entirely obscured by a slightly larger concentric occlusion	Yes	When the Moon is close to perigee (or assisted by the Earth being at aphelion) during an eclipse, the Moon's apparent size is slightly larger than that of the Sun and will cover the whole solar disc. This is an astronomically useful effect, as well as aesthetically interesting to look at, as observers can study solar prominences and the atmosphere of the Sun whilst not being blinded by the glare of the bright 'surface' of the star, as well as being able to study and prove relativistic effects.
Annular	Sun partly obscured by a slightly smaller concentric occlusion	Yes	With the Moon nearer its apogee (and/or the Earth at perihelion), the Sun has a larger angular size than the Moon and will not be totally covered even by the most central alignment of each body. An eclipse can also be called "hybrid" (not illustrated in the diagram), by being seen as both Total and Annular by different observers. Those viewing at more extreme latitudes or more westerly/easterly (the eclipse being closer to dawn and dusk, local time) are viewing both Moon and Sun from slightly further away around the curve of the planet and, as such, the nearer Moon decreases in angular size proportionately greater than the much more distant Sun. Thus they may see annularity in the same eclipse for which others would see totality.
Oblate	Oval Sun obscured by a concentric circle, except for at the edges of its major axis	No	If the Sun were a grossly exaggerated oblate (or prolate) spheroid, for any reason, the equatorial (or polar) bulge might extend significantly beyond the original limits of totality, or the narrower radii fall beneath the limits of the nominally annular occlusion. Here the Sun has a visibly pronounced ovality and the Moon a lesser one (but roughly at right-angles, to add to the disparity). As the current effects that might cause each body to be oblate act in roughly the same plane as each other (both Sun and Moon spin upon roughly the same axis, with respect to the background), it would take more than merely an extreme increase in each's rotation to duplicate this image - however either could be accomplished.
Interior	Sun obscured at its edge by a thick ring, leaving its center visible	No	When an occluding object visibly larger than the Sun has a significant hole in the middle (like a torus, which is a doughnut-like shape), only the rim of the Sun is blocked in an 'inversion' of the annular eclipse. This could be considered as an extension to the oblate eclipse, as a torus shaped celestial object is possible by the laws of physics if the rotation was fast enough to prevent self-rounding by gravity. (Or it could have 70% of it removed, like in the manga Assassination Classroom.)
Cuboid	Sun obscured by a square cross-section	No	In this example, the 'Moon' appears to be a cube-like shape, rather than spherical, thus eclipsing a square portion of the solar disk. It must be turned face-on to Earth (and Sun), as other orientations of a true cubic (or cuboid) object might cause a rectangular or even hexagonal 'shadow'. It is twisted in the other axis (to be a diamond, rather than aligned square), but this will always be a matter more of one's precise viewing point upon the surface of the Earth regardless of the orbital and rotational alignments. This might be a reference to the video game Q.U.B.E., where a massive, cube-like alien spaceship passes by the Moon and threatens to hit the Earth.
Transverse	Obscuring circle drawn as a perpendicular plane intersecting the Sun on a center-line	No	This depicts the solar disc as two dimensional (and at an oblique angle) and the Moon (or its shadow) as a second 2D object somehow passing through the same space. This may be a spoof on the 'flat Earth' explanation for the solar eclipse. Additionally, as the 2-D Moon is not obscuring the bottom half of the 2-D Sun, this suggests that the two are at an equal distance (or the Moon is further away), similar to the hug eclipse mentioned last. The intersection of 2D objects in 3D space is the topic of a book, Flatland: A Romance of Many Dimensions, that Munroe has referenced repeatedly, such as in 721: Flatland.
Saturnian	Obscuring circle is given an oblique (shadow) ring system	Yes, but not from Earth	Probes sent to Saturn have captured images of this type of eclipse. While it is theoretically possible that Saturn (and its rings) could eventually find itself in a position to cause a solar eclipse on Earth (and/or that Earth moves beyond Saturn, or that the Moon gains significant debris rings in its own right), this scenario does not appear to be likely any time soon.[citation needed] There are Saturnian moons that naturally travel behind their parent planet, but none currently known to be so far from Saturn that they would ever see the Sun and Saturn at similar apparent sizes, and no human is yet in a position to directly see such an effect by any currently available means.
Hug	Obscuring shape is pinched over at both sides by the respective overlapping edges of the Sun	No	In this image it appears the Sun has extended its 'limbs' to affectionately hold the Moon, which might be problematic in several different ways,[citation needed] some of which are humorously mentioned in the title text.

In the title text, the hug eclipse is mentioned again (which is of course, not practically possible as the Sun is about 93 million miles, or 150 million kilometers, away from the Moon (and Earth)), this time in regards to where the best location would be to observe the event. First, normal advice is given about how the best way to view the eclipse (just like actual eclipses) would be in a scenic and natural area, predicted to have few clouds at the time, from somewhere along the rather narrow 'track of totality' for the day.

Then he mentions that the lunar surface would be the worst place to go in a solar hug, because even if it was somehow moved into touching distance by advanced sci-fi tech or a terrible disaster, the Moon would vaporize on contact with the Sun's plasma, thus not allowing for any sort of hug. In fact, we would not live very long if this happened, as the Earth would also be baked by the Sun's light, then swallowed by its intense gravity.

Additionally, a normal Sun-Moon-Earth eclipse seen from the Moon would either be ineffectual or perfectly normal 'night-time', depending upon your lunar location. A Sun-Earth-Moon eclipse, seen from the Moon would be far more than total (if sought for from the nearside face) due to the much larger size of the Earth blotting out much more of the background, although the 'circular sunset' that gives the fully eclipsed Moon a dull red illumination could be worth seeing.

In all these images, the solar disc does not actually have a solid Moon in front of it, but a semi-transparent shadow, more typical of the representation of the Earth's solar shadow as it passes across the face of the Moon in a lunar eclipse. This may be an additional part of the humor, but it is likely an artistic choice made to improve the diagrams' legibility.