# Tag Info

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### Usage of $\sim$, $\approx$, $\simeq$, and $\cong$ in observational astronomy?

$\simeq$ and $\approx$ both mean "approximately equal to". I don't think $\cong$ is used so often, but if I read it, I would interpret is as the same as the two others. $\sim$ in principle means "of ...
• 32.3k
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### Superscript-subscript uncertainty notation

When quoted like this they would usually be the most likely value (peak of the probability distribution) or the median value (where half the distribution is above or below), and then the superscripts ...
• 116k
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### What abbreviations, letters, or symbols do we use to denote highly degenerate stars?

Neutron stars and black holes do not have assigned spectral types since they do not have a measurable optical/IR spectrum - which is the basis for assigning a spectral type. There are many ...
• 116k
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### What does Sa and Sab mean for spiral galaxies?

Capitalization is critical here. (As is knowing which classification system is being used.) The traditional spiral stages (going back to Hubble) are Sa - Sb - Sc; this was a sequence from more ...
• 14.7k

### What symbol is used for the moon when doing calculations?

There is no authorative standard - you can use what you want, as long as it is clear what you mean. Besides that: yes, ☽ is reasonably standard. Often also written indices like $M_{moon}$ or $M_m$ are ...
• 11.1k
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• 21
1 vote

### Usage of $\sim$, $\approx$, $\simeq$, and $\cong$ in observational astronomy?

As an (ex) professional astronomer, I can tell you that there are no rules that are followed. There are very very few exact measurements in Astronomy, x rarely technically equals anything. In ...
1 vote

### Usage of $\sim$, $\approx$, $\simeq$, and $\cong$ in observational astronomy?

Wikipedia (where would we be without it) has a handy list of mathematical symbols which is pretty useful in this context. Note that in particular : $\sim$ will crop up often as meaning ...
1 vote
Accepted

### From Mean Moon to True Moon in an old procedural calendar

How would you interpret this? "(1780 + 80) * 3 on base 808, and add 2" As before, there is a confusing avoidance of specifying the unit under consideration, but the pattern is still that the last ...
• 7,674

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