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| Cosmic Distance Calibration |
 Title text: This is the biggest breakthrough since astronomers noticed that the little crosshairs around red giant stars starting to burn helium are all the same size. |
Explanation
The comic interprets the UI labels next to the stars as actual objects in space, which is absurd.[citation needed] If these labels were to become astrophysical objects in reality, it would quickly result in major changes to the universe. As each of these labels would need to be clearly visible from an observatory, they would require monstrous size, maybe even big enough to collapse into black holes when pointing to stars farther away. They would also create a sudden lack of need for themselves, as the stars would be gravitationally attracted to their respective labels and promptly destroyed.
The label on the billboard appears to be pointing to a star in the spiral Galaxy M106, located between 22 and 25 million light-years away from earth.
The title text refers to crosshairs, a pair of perpendicularly intersecting lines most commonly associated with telescopic sights for aiming firearms. This seems to be referring to the diffraction pattern caused by the arms holding the secondary mirror in most telescopes, causing a star to appear to have several "spikes" radially outward.
Of course these aren't physical objects next around the star, they are (as mentioned) created in the telescope.
The size of the diffraction spikes is correlated with the luminosity of the star being viewed. Red giant stars starting to burn helium have the same size diffraction spikes* because they are the same absolute brightness. They are "Tip of the Red Giant Branch" standard candles, the fact that they have the same absolute brightness makes them essential for cosmic distance measuring, since the observed luminosity is a simple inverse-distance-squared falloff from a known original value.
*: Randall is taking a little bit of license here, the spikes depend on luminosity, whereas the stars in question have the same brightness, which is not the same thing.
Transcript
- [Ponytail is at a lectern, pointing at an image of intergalactic space. There is an image that shows a zoomed-in label beneath a star with 4 points. The zoomed-in label shows three lines of text, some of it partially cut off:]
- M106 0-06 [cut-off]
- Distance:
- 23.6163 MLY
- [Caption below the panel:]
- Cosmology News: New telescopes are finally powerful enough to read the little labels next to stars showing how far away they are.
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