Editing 2596: Galaxies

{{comic
| number    = 2596
| date      = March 21, 2022
| title     = Galaxies
| image     = galaxies.png
| titletext = I know it seems overwhelming, but don't worry; I'm sure most of them have only a few stars, and probably no planets.
}}

==Explanation==
{{Quote|Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is.|{{w|Douglas Adams}}|{{w|The Hitchhiker's Guide to the Galaxy}}}}

This is another comic with a [[:Category:Facts|Fact]], the second in a row of these fact comics to use an Astronomy fact.

Our best approximation of the number of {{w|galaxies}} in the {{w|observable universe}} is about 200 billion (2 × 10<sup>11</sup>). That's a lot of galaxies, and here [[Randall]] exemplifies this by showing a small circle and estimating that when the comic's picture is viewed at a typical arm's length, expanded to full screen on your typical smartphone, the circle contains roughly 50,000 galaxies (that means of course not the small circle itself, but the volume defined by the viewers eye, that circle, and an onward conical extension into deep space — and simultaneously back in time — to the respective limits of the observable universe). Most of those far-away galaxies are undetectable by even our most powerful astronomical instruments today, and comparatively few could be seen (let alone positively identified as such) by the naked eye. For example, in the {{w|Hubble Deep Field}}, an image of a small region in the constellation Ursa Major, about 3,000 visible galaxies can be identified.

The dot size is subjective, but it can reasonably be taken to be 1mm diameter, 0.5mm radius, total area π r<sup>2</sup> or about π/4 square millimeters. You're probably holding the phone about a half a meter away from your eye. The surface area of a sphere is 4 π r<sup>2</sup>. With a radius of one-half meter, that comes out to be π square meters. Thus, the area of the circle is about 1/4000000 of the area of the sphere, 200 billion galaxies divided by 4 million is the 50,000 average mentioned in the cartoon. A similar mathematics was used for the comic [[1276: Angular Size]], in which the projective sphere was at the Earth's own radius and cross-sectional areas of objects were compared, rather than an approximate count of objects within a given angular spread. 

While galaxies usually are between 3,000 to 300,000 {{w|light-years}} across and contain between 10^8 (100 million) and 10^14 (100 trillion) stars, most are so far away from the Earth (upwards of billions of light-years) that they are invisible to the naked eye, or even through most telescopes. When magnified across such vast distances, even something as small as a pinhole expands to huge sizes, easily able to fit tens of thousands of galaxies.

The premise of this comic is that although galaxies are giant, space is <i>unimaginably</i> big and contains a vast number of things. Randall is apparently overwhelmed by this, as shown in the caption: ''Astronomy Fact: There are too many galaxies''. 

The title text is Randall reassuring his readers why not to worry of this overwhelming fact. He states that most galaxies only have few stars and probably no planets. However, as mentioned above each galaxy contains a huge amount of stars, and as evident from all his own comics about [[:Category:Exoplanets|exoplanets]], it is now clear that many of the stars in a galaxy also have planets orbiting them. Thus the number of stars and planets in that small circle is much more mind-bogglingly large, than the number of galaxies, and thus the reassurance is sarcasm.

In [[975: Occulting Telescope]] [[Cueball]] expresses a similar sentiment about the number of stars.

==Transcript==
:[An almost white panel with a caption at the top. Then a small circle, much smaller than for instance the letter O in the text is in the center of the panel. A bending arrow points to the circle and beneath the arrow is a caption.]
:Open this picture fullscreen on your phone and hold it at arm's length.
:There are 50,000 galaxies in this circle.

:[Caption below the panel:]
:Astronomy Fact: There are too many galaxies.

{{comic discussion}}

[[Category:Facts]]
[[Category:Astronomy]]