Astronomy Stack Exchange
Astronomy Stack Exchange

Questions tagged [units]

Use for questions about standards of measurement used for different types of quantities, and for conversions between units.

Units are standards for measurement of physical quantities. Metrology is the science of developing nationally and internationally accepted units of measurement.

The most abundant unit system SI (Système international d'unités), consisting of seven seven base units: meter (length), kilogram (mass), second (time), ampere (current), kelvin (temperature), candela (luminous intensity), and mole (amount of substance). Units for other quantities are derived from these.

References

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Is the Earth-Sun distance 1.012 AU?

Wolfram Alpha's query: Sun Earth distance in AU gives: 1.012 au (astronomical units) They definitely use this value in other places too - e.g. Earth-Sun $L_1$ distances from Earth and from Sun don't add up to 1 AU - they are 0.01009 AU and…
SF.
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apparent size of an astronomical body

What's the name of the measure of apparent (visible) size of a body? e.g. the Sun and the Moon appear to be roughly the same size, despite the Sun being vastly bigger - because the Moon is much closer. What's this apparent size called?
SF.
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Units and some equations

I'm a grad student and I feel like this is an extremely elementary question that I should know, but I admit that I don't. Occasionally in science I find myself solving an equation for some answer where it feels like the units don't add up. For…
ObiDonKenobi
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How to convert apparent visual magnitude to SI units?

How do I convert the apparent visual magnitude of astronomical objects to SI units (lumens)?
Nicole Sharp
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Astrophysical "unitised" version of the Gravitational constant

This question relates formalising the gravitational constant, $G$, (which in S.I. units is usually quoted as $\sim6.67\times10^{-11}\,\mathrm{m}^{3}\,\mathrm{kg}^{-1}\,\mathrm{s}^{-2}$) in units which are more appropriate to astrophysics, such as in…
MichaelJRoberts
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What are some applicable problems with the correct usage of G?

In some fields of astrophysics, where distances are measured in parsecs (pc), velocities in kilometers per second (km/s) and masses in solar units (), it is useful to express G as approximately 4.302 x 10^-3 pc M^-1 (km/s)^2 ... Is G not…
Billy
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How to convert mW/m^2 to W/m^2/nm?

I have a vizier catalog with H-alpha fluxes as logF(Haplha) in units as mW/m^2. See sample data here: http://vizier.cds.unistra.fr/viz-bin/VizieR-3?-source=J/MNRAS/431/2/fluxes How do I convert mW/m^2 to W/m^2/nm or erg/s/cm^2/A? The first entry is…
Adrian
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