Title text: [One hill over, a competing astrophotographer does a backflip over a commercial airliner while throwing a tray of plastic space stations into the air, through which a falcon swoops to 'grab' the real one.]
Astrophotography is the practice of taking pictures of astronomical objects. Sometimes it is specified as a hobby, as opposed to the work of professional astronomers. Astrophotographers like to take pretty pictures of all sorts of objects in the sky, but photographing the Sun is a popular subgenre within the field, especially if something is transiting in front of it. Typical things include planes, the International Space Station (ISS), and the Moon (Solar eclipses).
Whilst the Total Solar Eclipse 2017 (which previously was a recurring theme on xkcd) was visible across US, it was possible to see the ISS pass in front of the Sun during a partial part of the Eclipse (from a site that was later in the total Eclipse zone). This was photographed and filmed by Destin from Smarter Every Day and can be seen in his video Space Station Transiting 2017 ECLIPSE. (Go to the time of the flyby of the ISS in the video here).
Two years later he did another episode South American Eclipse - Argentina. In this video there was only the moon eclipsing the sun, at first, but then towards the end the sun begins to set behind the distant mountains creating a shadow scenario between Moon and mountain shadows as displayed in this comic.
This comic thus combines those two videos, which Randall must have seen, and then adds several more layers caused by the Astrophotography community's One-Upmanship. The practice of "one-upmanship" refers to the practice of achieving something superior to what another has achieved, or "getting one up on" them. The term originated in the 1950s or earlier.
The caption claims that the photo shown in the comic is the result of a continuous string of one-upmanship among astrophotographers in a community, each striving to one-up the other.
In this comic there seems to be an abundance of things:
- The ISS can be seen transiting in the upper center. (as in this picture)
- There is an ongoing partial solar eclipse so the view of the Sun is partially obscured by the Moon in the upper right quadrant.
- These two things are what Destin managed in his first video.
- The Sun is setting or rising from behind a hill while partially eclipsed.
- This is what Destin managed in his second video.
- This photographer achieved a combination of those two plus several other ones-up those two videos.
- Megan is standing slightly below the peak of a hill and seems to be juggling with five balls, which are also in front of the sun. One or more of those balls might actually be sunspots or the planets Mercury or Venus.
- Cueball is standing at the peak of the hill, shooting an arrow from a bow, one arrow has pierced what at first appears to be one of the juggling balls, but may be a Transit of Venus.
- It is unclear if Megan is juggling five balls and Cueball shot one, or if Megan is juggling four balls and Cueball put the fifth ball on the arrow before shooting it.
- A simultaneous Eclipse and Transit of Venus is actually expected in the future, but not until April 5, 15232 (13211 years after the publishing of this comic). That said, it would though likely be easier to make the arrow "hit" Venus than one of the juggled balls, as the planet's angular velocity is significantly lower.
- Two airplanes pulling banners with the words "nice" and "shot" (which could refer to both the archer and the photographer) are flying in opposite directions above them. (Airplane banners that are not continuous sheets are made with thin support lines spanning the openings, which explains the presence of the apparently unsupported central disc in the "O".)
- The central disc in the O could also be a perfectly-aligned circular sunspot.
Taking the picture required precisely scheduling and arranging the relative positions of several of the various subjects (and photographer) to coincide with the predictable but rare conjunctions of the rest of the scene, as well as special equipment:
- All this had to be timed very very precisely as the transit of the ISS only takes a second.
- A solar filter must be used to photograph the sun without overexposing the image or even damaging equipment.
- The photograph must be taken during a partial solar eclipse. These only happen a few times per year and are only visible in part of the world.
- The photographer must be quite far away with a telephoto lens to achieve the visual scale. A nearby person appears larger than the moon. It is possible to photograph the silhouette of a person or a cityscape in front of a full moon, making the moon look comparatively larger or smaller by adjusting the distance to the closer subject, and then the lenses used by the photographer to make them both fill just the right amount of the frame.
- The photographer would need to be approximately one kilometer distant if the image is a typical human scale. Both Sun and Moon have a visual angle of about 0.5 degrees. The characters are approximately 1/5 the Sun's height giving a 0.1 degree visual angle. A right triangle with a height of 1.7 meters (a typical human height) spanning 0.1 degrees for the side angle, the distance would be 974 meters (3195 feet) from Cueball and Megan.
- The photographer taking this image would need a high magnification 2-meter (2000mm) equivalent lens or a shorter lens with a cropped image to fill the frame as in the comic. Long telephoto lenses like those are uncommon for most photographers, but would be available among astrophotography groups.
- The exposure time of the photograph had to be short enough to capture clear silhouettes of the ISS, the juggling balls and the arrow while these were in the air.
- The mountain had to be in a location that would happen to see the ISS passing in front of the sun at the same time as the sun was rising from behind it.
- The subjects had to achieve a moment in which four juggling balls were in the air and an arrow had pierced the point where Venus would appear, while sideways relative to the sun's light, with still near normal intensity.
- The planes also needed to be flying in the correct directions for the text of the signs to be visible, and with very precise timing for them to be in the correct positions to read "Nice" as coming before "Shot" just as the ISS passes by.
- The sky (at least between the photographer and the Sun) had to be free of clouds.
The title text describes a similarly outlandish photo attempting to one-up Cueball and Megan, done simultaneously on the next hill over, thus a place where the same ISS transit can be seen:
- A commercial airliner is flying in front of the Sun, thus this has to be timed with the flight plan (or it has to be chartered), to pass there at the correct height and position, within a few seconds.
- The astrophotographer is performing a backflip such that they appear to be over the airliner.
- The astrophotographer is tossing several tiny models of the ISS from a tray, so they also appear in front of the Sun with the real one (like the juggling balls and Venus).
- A falcon is flying in front of the Sun, presumably intending to capture prey, in such a way that it appears to be snatching the real ISS out of the fakes. The falcon moves slowly compared to the ISS, so it just needs its talons to be on the line the ISS makes across the Sun, then a picture where it is close to the talons can be used. The other parts are slower than this.
- [Cueball and Megan stand on a hill with the dark yellow sun setting behind them. Outside the Sun's disc everything is black. All that can be seen is silhouettes against the sun. Cueball is at the top-left of the hill, holding a bow in his left arm, which has been recently shot, as indicated with lines along the string. The the arrow is to right, where it has speared a ball. Megan is at the bottom-right of the hill, juggling four other balls, one near her hand, two above her and one higher up than the path of the arrow. There are two planes going in opposite directions with banners on them with words readable against the Sun. Above the planes is the shadow of the International Space Station. Finally Sun is partially eclipsed by the moon in the upper right corner.]
- [Banner 1]: Nice
- [Banner 2]: Shot
- [Caption beneath the panel]:
- Our astrophotography community's one-upsmanship[sic] is getting out of hand.
- Randall has commented on extreme photography in comics 1855: Telephoto and 1719: Superzoom, and the How To chapter "How to take a selfie".
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