3219: Planets and Bright Stars

2026-04-07T03:35:56Z

2600:8801:E821:4500:DD48:A092:58EC:C619:

{{comic
| number = 3219
| date = March 13, 2026
| title = Planets and Bright Stars
| image = planets_and_bright_stars_2x.png
| imagesize = 374x265px
| noexpand = true
| titletext = An old astronomer trick for distinguishing the Sun from other stars is to take multiple photos a few minutes apart and overlay them, making the Sun stand out due to its high proper motion.
}}

==Explanation==
This comic shows an identification chart for some of the planets and bright stars visible at night from Earth. Bright shiny objects in the sky are often confused with each other by people without astronomical experience. The chart is supposed to make identification easier by placing them adjacent to one another to highlight the differences. However, all 12 dots are nearly identical, making the chart useless.

The real way of distinguishing these objects is by their relative position in the sky. In particular, stars can be found using constellations, which are an apparent pattern of bright stars that make different regions of the sky distinguishable from one another. The planets can be distinguished by not belonging to the constellations, and further differentiated by their color, brightness and movement relative to the stars (on the scale of weeks or months).

The stars and planets do indeed look similar to one another in reality, but they are not identical. Some of them (in particular, the star Betelgeuse and the planet Mars) have a distinct reddish color, which can be seen in good conditions. The brightness is also different, and it can serve as a guide, but it's difficult to precisely judge brightness by eye, and the planets don't have a constant brightness over time. The differences are actually visible in the comic to a degree (e.g., the spots for {{w|Venus}} and {{w|Jupiter}} are slightly larger than the others — Venus is an Earth-sized planet that is relatively close at the times we can actually see its brightly lit sunward side — the much more distant Jupiter because it's the ''largest'' planet in the solar system), but they're subtle enough to not be recognizable at first glance.

Each 'object' in the comic also has a color, albeit ''extremely'' desaturated (very nearly white). If deliberately exaggerated, the comic's planets and stars are all notably non-white, as can be seen in the picture in the [[#Trivia|trivia section]] below..
*Planets:
**{{w|Venus}}: the yellowy-orange hue of its cloud layers.
**{{w|Mars}}: the red of its surface (given more muted saturation, in the comic, for the joke to work?).
**{{w|Jupiter}}: the general orange hue of its combined cloud layers.
**{{w|Saturn}}: a more 'peachy' orange of its clouds (no obvious hint of its ring system).
**{{w|Mercury (planet)|Mercury}}: a yellow surface (not typically noted, in true-hue images, perhaps artistic license from its proximity to the {{w|Sun}}).
*Stars
**{{w|Sirius}} (binary system, primarily a {{w|main sequence}} A-type star): light blue.
**{{w|Procyon}} ({{w|subgiant}} F-type star): more light green, or yellowy-blue/cyan.
**{{w|Antares}} (M-type star, {{w|red supergiant}}): orange.
**{{w|Altair}} (A-type, main sequence): light blue.
**{{w|Betelgeuse}} (M-type, {{w|red supergiant}}): relatively dark red (usually visible as such in real eyes-only observations).
**{{w|Vega}} (A-type, main sequence): light blue.
**{{w|Polaris}} (ternary star-system, dominant member being an F-type {{w|yellow supergiant}}): ''extremely'' unsaturated cyan.

Using even a small telescope would make it easy to distinguish the planets by their brightness, size, and surface features. Additionally, using a spectroscope would allow for a measurement of the star's spectrum, which coupled with its brightness would allow an astronomer to distinguish the mentioned stars.

The title text suggests a "trick" for recognizing the Sun among other stars, suggesting measuring its {{w|proper motion}} by overlaying several images. Proper motion is a measure of the change in apparent position against the more distant 'fixed' background of stars, as an {{w|angular rate}} (like degrees/second). This {{w|Time-domain astronomy#History|astronomically useful}} trick is similar in principle to a {{w|blink comparator}}. It would indeed differentiate it from other stars, but there are much easier methods, such as its extreme brightness and large angular size.{{cn}} A disadvantage of the proposed method is that it distinguishes the Sun from other stars, but it cannot distinguish the Sun from planets. A further disadvantage is that pointing any ordinary camera at the Sun could damage the imaging part of the camera (which could be used as a form of identification, as no other star does as such from Earth), and pointing a typical wide-aperture astronomical telescope at it would be very likely to do so. It is also completely unnecessary, except during a {{w|solar eclipse}}, because other stars are not usually visible during the day, when the Sun is out.

Additionally, "proper motion" is not a term usually applied to the Sun, which ''from the Earth'' moves entirely round the sky either once a year (according to the background of stars, albeit obscured by its daylight) or once a day (relative to the Earth's surface — but then so do the stars, over {{w|Sidereal time|''almost'' the same period}}, and this is not at all treated as proper motion). A more technically accurate reference would relate to the motion compared to itself (i.e. zero and meaningless) or the more {{w|International Celestial Reference System and its realizations|precisely applied}} gravitational centre of the solar system (which it wobbles around once in roughly twelve years, due to mainly co-orbiting with Jupiter). With objects for which proper motion is typically measured, the choice of using the any of these 'origins' (that do not rotate with the Earth's surface) is not significantly different, but {{w|parallax}} from Earth's orbit (or even a space telescope's own orbit) may still need to be accounted for in precisely tracking the closest stars, and plays a large part in the apparent movement of all other potential targets in the solar system itself.

==Transcript==
:[An array of four columns and three rows of white dots are displayed on a black background. Above them there is caption in white text. Below each white dot there is a label in white. The dots are almost identical, slightly fuzzy and 'white'. There are ''very'' slight color hues to the dots, and very minor differences in size, but they are not clearly visible unless the image is enhanced.]
:[Caption text:] Planets and Bright Stars identification chart
:[Dot labels, in reading order:]
:[Top row:]   Venus     Mars     Jupiter     Saturn
:[Middle row:]   Mercury     Sirius     Procyon     Antares
:[Bottom row:]   Altair     Betelgeuse     Vega     Polaris

==Trivia==
*[[User:Rumbling7145]] made this picture enhancing the colors of the dots in the original comic:
[[File:3219_planets-and-bright-stars-2x-saturation.png]]

{{comic discussion}}<noinclude>

[[Category:Comics with color]]
[[Category:Astronomy]]

explain xkcd - User contributions [en]

3219: Planets and Bright Stars