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Comment by exhilaration | Hacker News Reader

We report discovery of a bright, nearby (G = 13.8; d = 480pc) Sun-like star orbiting a dark object.

Can anyone explain these two units - G and pc. I'm assuming d is distance? I've googled it but can't figure them out.

G is the apparent magnitude in the green part of the spectrum. Astronomers have a standardised set of optical bandpass filters to record the brightness of a star at various wavelengths - U (ultraviolet), B (blue), V (visual), G (green), etc. Using the letter ID of the filter to mean "apparent magnitude as seen through this filter" is a common convention.

G is for "Gaia," not "green." This is a wide band that covers most of the visible part of the spectrum.

See: https://www.cosmos.esa.int/web/gaia/iow_20180316

G refers to the apparent magnitude[0] in the main filter used by the European Space Agency's Gaia space telescope (one of the most important scientific missions going on right now, though the public is less aware of it than, say, JWST).[1,2]

pc refers to "parsec," a unit of distance approximately equal to 3.3 light years. Parsecs are a natural unit of distance, because a star that is one parsec away has a yearly parallax "wobble" of one arcsecond (not by accident - this is how the parsec is defined). Parallax is the fundamental way in which distances to nearby stars are measured, so parsecs are the natural unit to use. Every greater distance in astronomy is defined with reference to parsecs: kiloparsecs, Megaparsecs, Gigaparsecs, ...

0. https://en.wikipedia.org/wiki/Apparent_magnitude

1. https://en.wikipedia.org/wiki/Gaia_(spacecraft)

2. https://www.esa.int/Science_Exploration/Space_Science/Gaia

pc = Parsec :) https://en.wikipedia.org/wiki/Parsec

I don't know what the G stands for. Possibly luminosity of some kind?

Brightness seems to be measured as apparent magnitude but that's denoted by m https://en.wikipedia.org/wiki/Apparent_magnitude

I think G is Stellar Classification https://en.wikipedia.org/wiki/Stellar_classification#Class_G which would mean this new star is the same class as our Sun.

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