2816: Types of Solar Eclipse

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Types of Solar Eclipse

Title text: The best place to be for a hug eclipse is a scenic natural area with good views and few clouds. The worst place to be is the lunar surface.

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, 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.

Transcript

This transcript is incomplete. Please help editing it! Thanks.

[Nine diagrams of solar eclipses are shown in a 3x3 grid layout. The first three are all real solar eclipses, the rest are all fictitious.]

Caption: Types of Solar Eclipse

[The Sun is partially covered by a similarly sized Moon:] Partial

[The Sun is completely covered by a similarly sized Moon:] Total

[The Sun is partially covered by a slightly smaller Moon, surrounding its shadow:] Annular

[An oval 'sun' is mostly covered by a round Moon, except at the extremes of its distortions:] Oblate

[Sun partially covered by a similarly sized 'moon', except for a hole in this moon's center:] Interior

[Sun partially covered by a square 'moon'-shadow, turned by an arbitrary angle:] Cuboid

[2D 'sun' being intersected with a 2D 'moon' at a perpendicular angle:] Transverse

[Sun being partially obscured by a body that has a prominent multi-ring system:] Saturnian

[Moon is pinched at the sides by the Sun behind it, as if being grabbed:] Hug

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Discussion

Is the annular eclipse actually possible? 162.158.78.118 21:24, 16 August 2023 (UTC)

Yes. https://solarsystem.nasa.gov/eclipses/2023/oct-14-annular/where-when/ 172.69.33.7 21:34, 16 August 2023 (UTC)

I interpret the Hug Eclipse as the sun wrapping around the moon giving it a hug, rather than the moon being pinched in on the sides. 172.70.211.62 21:38, 16 August 2023 (UTC)

I amended that (twice, first time got blitzed in an Edit Conflict situation), when I thought of a better way (two slightly different better ways! ...might not even have used the better one, in instance #2) to describe it. But I rushed a bit anyway... I can see typos. (Not including the likes of "centre", which is not a typo but me defaulting to British English by default; though no doubt that 'needs' changing too.)

I'm still wondering if just "label" and "description" columns are needed (image details can be recycled into Transcript, per label). Or if it could be ";header" and ":...description" without the table, but I think it looks no worse than I had feared, as the current table form. Of course, others have added more prosaic explanation paragraphs, so I'll let it sit a while. Almost certainly the other active editors here are going to have ideas about how to merge/expunge my efforts, and I'll let them copyedit my errors/'errors' as well. But at least there's a framework answer (or several) now. 172.70.162.179 22:20, 16 August 2023 (UTC)

That must be a VERY scary dragonite. 172.71.26.153 02:20, 17 August 2023 (UTC)

I think I need an explain XKCD for the dragonite reference in the bot joke... 172.70.210.160 16:49, 17 August 2023 (UTC)

Looks like it was originally just a dragon (consistent with various actual eclipse-myths). I'm not so sure whether it became a Pokemon creature (does that have Sun-eating capabilities?), which seems to be the main searchable reference, or something even less known to me. 172.70.86.63 17:17, 17 August 2023 (UTC)

Presumably it's a dragon which has survived its atmospheric entry and landed on the earth's surface.172.70.85.219 16:10, 18 August 2023 (UTC)

I love this community, which will explain how a solar panel works and why the moon cannot give the sun a hug with the same level of rigor and detail. 172.69.247.40 04:26, 17 August 2023 (UTC)

Arguably, the Sun is constantly hugging the Moon, through the warming arms of the Solar Winds.172.70.86.39 16:15, 18 August 2023 (UTC)

I have always wondered about solar eclipses... does anybody else think it's really weird that the Earth is not just the only planet with exactly the right ratios of star/satellite size/distance to make eclipses happen, but is also the only planet (so far as we know) where there's an evolved intelligence that can appreciate such a phenomenon? After all, a similar effect viewable only from Mars or Venus would be totally wasted... 172.70.91.161 06:35, 17 August 2023 (UTC)

It is indeed a weird thing. We don't know if it is a weird thing that is of significance for life or intelligence or civilisation, or if it is just a happenstance weird thing. The universe has all kinds of weird things. --162.158.74.22 07:22, 17 August 2023 (UTC)

"Right place, right time". It helps that we have a Moon roughly the same (angular) size of the Sun, which seems rare, but if we didn't know it was a thing then we might not miss the coincidence. And, because of the slightly drifting Moon, at some time in the past (tens/hundreds of millions of years ago), we never had annular eclipses – but then very few people appreciated that. In another few millions of years, we'll lose all possibility of total eclipses (imagine being there to witness that last one, everyone who makes effort to be there cramming into the short stretch of 'final, brief totality' in the literally-ultimate hybrid eclipse...).

On human scales, it's a fairly wide window that may very well out-spread the full reach of humanity (in fact, I'd bet on it, but do feel free to try to collect if we're both there jostling for room in that 'last eclipse sweet-spot' viewing platform). But imagine all the other astronomical co-inky-dinks that we might have witnessed if humanity were significantly shifted by time (and place) in the universe. Instead of "very edge of totality" eclipses, who knows what else might have been (surprisingly-)'normal'... Or at least totally different (not-)Earth (not-)Moon (not-)Sun eclipse combinations that are right-sized just like ours is. 172.70.91.69 08:49, 17 August 2023 (UTC)

postscript: of course, if large moons (created like ours was supposed to be) had to be settled down enough to allow life (after the Thea-like impact) but significant enough to cause tides (variously theorised as driving the chemical creation of life, if not the later development of advanced life forms or even the prerequisites of civilisation leading to scientific enquiry) then perhaps the chances of any equivalent beings to ourselves having any equivalent eclipses to what we see is slightly raised above that of 'any random planet with or without appreciative audience'. But, until we get very good at surveying exoplanetary systems (if we ever do) and/or visit them ourselves (ditto, with bells on), it'll be hard to quantify any inherant tendency to serve such things up on a platter to all those who might appreciate it. 172.70.91.69 (again) 09:07ish, 17 August 2023 (UTC)

I don't understand your 'evolved intelligence'. Whether planet that has intelligence is very not-correlated with its capacity to create eclipses. 172.69.71.36 18:40, 17 August 2023 (UTC)

SFAIK, there's no evidence from which to base any kind of correlation/non-correlation/anti-correlation between intelligence and eclipses, given that we have only one instance of a planet with intelligence upon it to study (and we might even learn of further eclipse-worthy planets well before we do of intelligence-populated ones). Speculative reasoning can try to fill in gaps, maybe (see just above), as long as one realises it's wild-ass-guessing. But, luckily, the thing you're replying to doesn't even try to suggest that by any reasonable reading of it. 172.71.242.65 21:25, 17 August 2023 (UTC)

By the time you see the cuboid eclipse, it's already too late. Resistance is futile. ProphetZarquon (talk) 23:52, 17 August 2023 (UTC)

Not for everyone. The weak will perish. -- Hkmaly (talk) 20:33, 18 August 2023 (UTC)

Given that the moon is slightly oblate, would an oblate eclipse be possible when the angular sizes of the moon and sun are almost the same? EHusmark (talk) 09:11, 18 August 2023 (UTC)

A good question, but the diagram shows the sun as being oblate, so I don't think the intention was to reference the slight (but real) oblate nature of the moon. Good catch, though. Dextrous Fred (talk) 16:54, 18 August 2023 (UTC)

The Moon has an equatorial diameter of ~3576.2km, polar diameter of ~3472.0km. 104ish km difference. The Sun is near-spherical, said to be less than 10km difference between equatorial and polar diameters, which projected inwards to 'Moon equivalent distance' is even more practically zero. But as it would be distorted at roughly the same angle as the Moon (spin axis of each varyies maybe +/-5 degrees, depending on what point of each orbit everything is) it would always be <105km difference so long as the Sun's oblativity weren't double that of the Moon (or prolate to any degree). Moon-'mountains' seem to be about 2.5km high, so local rim-variations won't actually add/subtract much from any oval-adjustments.

Anyway, 90km in 3500km(+/-) is around a quarter of a percent of variation. And a handful of millionths of a degree, subtended to the Earth observer, if my best-/worst-case calculations that I just did are correct (roughly 1/60th of an arc-second is one of the answers I pulled out, in case anyone wants to sanity-check what I just did on the back of this 'ere envelope). 172.69.79.153 18:56, 18 August 2023 (UTC)

"A normal Sun-Moon-Earth eclipse seen from the Moon would either be ineffectual or perfectly normal 'night-time'" -- The shadow on the Earth should be visible from the dark side, probably with the naked eye but certainly with modest optics. Perhaps it's not dramatic but it would still be interesting.162.158.159.80 03:16, 19 August 2023 (UTC)

Yes, here's an example: NASA picture of Moon's shadow during solar eclipse Admiral Memo (talk) 05:53, 19 August 2023 (UTC)

As the author of the phrase, to clarify that I was refering mostly to: 1) ineffectual because you're sunlit on the far side and can't see the Earth at all, or 2) 'normal night-time' (ok, not perfectly, but nearly so) because you have a 99.9999...% "full-Earth" amount of earthshine illuminating you. As opposed to Earth-viewed eclipses where all (direct/reflected) illumination is conspicuously absent for a number of minutes. (Or much, for partial(solar/lunar) or annular(solar).)

Being on the Moon for a lunar-eclipse (even partial, if you're somewhere on the right bit) is far more significant. Unless you're on the far-side, in which case it's an extreme non-event just as being there during the solar eclipse is (but 'essentially normal night' instead of 'essentially normal day').

Perhaps some fun could be had by being out on the limbs/poles of the lunar surface, raised high enough against the local surface to have significant 'both sides' experience (become an actual bailey's bead/miniscule gap between them? ...not that it would be personally so obvious as such). Just remember to account for libration, when you choose your spot! ;) 172.71.242.193 09:49, 19 August 2023 (UTC)