Editing 2707: Astronomy Numbers

{{comic
| number    = 2707
| date      = December 5, 2022
| title     = Astronomy Numbers
| image     = astronomy_numbers_2x.png
| imagesize = 593x315px
| noexpand  = true
| titletext = I adopted a cat that weighs 12 solar masses. Laser pointers love chasing it.
}}

==Explanation==

Space [https://neal.fun/size-of-space/ is big], to the point that it regularly defies our earthly notions of scale. As a result, most quantities in astronomy have huge scales beyond anything that humans regularly experience or measure. (In fact, the word "astronomical" is sometimes used colloquially to describe any extremely large quantity).

For example, Earth has a mass 10<sup>23</sup> times more than the average human, and the Sun is 10<sup>5</sup> times more than that, which itself is 10<sup>12</sup> times less massive than the Milky Way. The same applies to speeds, distances, and time, which can often be measured in terms of light speed, light-years, and millions or billions of years. Because of this, it's a truly unusual occurrence for anything in space to end up in the fairly narrow range of scales of mass, size, speed, or time that humans can easily grasp.

[[Ponytail]], apparently a scientist researching something related to Earth's orbit, finds that on a particular date, Earth will be approaching the sun at a velocity of 65 miles per hour. To American ears, this is a very normal sounding value (i.e. the speed of a fast-moving vehicle, often used as a speed limit on highways in the US). As Ponytail is accustomed to astronomical values, she is thrown off by this, and remarks that she finds it "suspicious" when reasonably human-scaled numbers come up in astronomy.

However, Ponytail seems to take this philosophy to an absurd degree by insisting that ''all'' scales should be as incomprehensible as astronomical ones, even those used for human-scale measurements, such as the weight of cats. In the third panel, the vet, [[Megan]], is seemingly used to this problem (perhaps she gets a lot of astronomers, or Ponytail has a hypochondriac cat), so she restates the 12-lb weight of Ponytail's cat in solar masses. Since using this unit yields an ''incredibly'' small number, 3×10<sup>-30</sup> (a three preceded by a decimal point and 29 zeroes), it satisfies Ponytail's need for incomprehensibly-scaled values. This weight is in fact about 13 lb 2 oz (about 5.5 kilograms), slightly heavier than the initial figure given for the cat, but within [[2585: Rounding|rounding error]] for the single digit of precision that Megan uses.

The Earth's orbital velocity around the Sun is far above normal human scales (around 30 kilometers per second or 108,000 kilometers per hour). However, Earth has a fairly circular orbit around the Sun, so most of this speed ends up being tangential (sideways) rather than radial (towards or away from) the Sun, which is the value relevant for Ponytail's calculations. On January 1 (the date being discussed in the comic), Earth's radial velocity is close to its smallest value because we reach our closest point to the Sun in the first few days of January each year (in 2023, {{w|Perihelion|perihelion}} happens on January 4). Thus, by January 1, the Earth's velocity toward the Sun is nearly zero before it starts traveling away from the Sun again. This is how Ponytail ended up with the "suspiciously" small value of 65 miles per hour.

On the other hand, by April 3, 2023, Earth will be receding from the Sun by almost 500 meters per second or 1800 kilometers per hour, which is a less normal speed for the average person to encounter in everyday life{{citation needed}}.

65 miles per hour is approximately equal to 105 kilometers per hour, although the even more typical scientific value (in {{w|International System of Units|SI}} derived units) would be 29 meters per second.

The title text makes a joke by reversing the typical cat behavior of [[729: Laser Pointer|chasing laser pointer dots]] by envisioning a cat with a mass equivalent to 12 solar masses. The {{w|Schwarzschild radius}} for an object of that mass would be around 36 kilometers, so a cat-sized object of that mass would be a black hole, and would therefore bend all nearby light (including that from the laser) inwards towards its singularity. But then it should also draw in the physical laser pointer device itself, if it is neither very far away nor in orbit.

==Transcript==
:[Ponytail is standing in front of a whiteboard writing on it with a pen, while Cueball looks over her shoulder from behind her. On the board is an almost circular ellipse with a cross that centers on a dot towards the left side of it. On the right side there is a small circle on the ellipse's line. There are several lines of wiggles representing unreadable text. To the left of the ellipse there are two lines near the top of and four near at the bottom of the ellipse. Ponytail is writing a fifth line below these almost under the ellipse. At the bottom to the left there is a rectangular frame with a line of text beneath it and at the bottom left corner there is a line forming a half closes rectangle around two dots.]
:Ponytail: …And we need to correct for our elliptical orbit. On January 1<sup>st</sup>, Earth will be approaching the sun at a rate of ...let's see...
:Ponytail: 65 miles per hour.
:Ponytail: Weird. Okay.
:Cueball: Weird?

:[Ponytail has turned towards Cueball, the pen is no longer in her hand and the white board is no longer shown.]
:Ponytail: I get suspicious whenever I see a normal number in astronomy. We're not supposed to have those. Feels wrong.
:Ponytail: Scales should all be incomprehensible.

:[Across the top of the next panel there is a label:]
:Earlier, at the vet:
:[Megan in a lab-coat raises her hand palm up towards an animal carrier cage standing on her desk. The cage has a handle and five air holes are at the top. Behind two of them something black inside the cage can be seen. Ponytail is standing on the other side of the desk looking at Megan.]
:Megan: Your cat weighs 12 lbs.
:Ponytail: Ridiculous, nothing weighs "12". You must mean 10<sup>-20</sup>? Or 10<sup>40</sup>?
:Megan: Fine. Your cat weighs 3x10<sup>-30</sup> solar masses.
:Ponytail: Okay. Better.

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Megan]]
[[Category:Astronomy]]
[[Category:Cats]]