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1

The electromagnetic spectrum is a continuous distribution of frequencies/wavelengths. Photometry is the science of light as perceived by the human eye, so it is very relevant for observing astronomical objects with telescopes, etc... In astrophotometry, one cuts the electromagnetic spectrum into bins, called "magnitudes." The specific ranges of ...


2

The Gaia EDR3 catalogue gives a parallax of $10.965 \pm 0.028$ milli-arcseconds. This differs from the DR2 parallax by 0.115 milli-arcseconds. This is not unexpected because there are systematic errors of order 0.1 milli-arcsec in the DR2 parallaxes. The new EDR3 parallax is expected to have systematic errors that are no bigger than the statistical error bar ...


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Parsec or Parallax-arcsecond is defined as the 'distance' of something that has a parallax angle of one arc second. The International Astronomical Union (IAU) define 1 parsec(pc) as: $$1 \text{pc} = 1/\tan(1'') \ \text{au}$$ $$\Rightarrow 1 \text{pc} = 1/\tan({1\over60}') \ \text{au}$$ $$\Rightarrow 1 \text{pc} = 1/\tan({1\over60\times60}^{\circ}) \ \text{au}...


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Distance to galaxies are measured using "standard candles": these objects are well-known astrophysical sources which have a known luminosity. Examples include Cepheid variables, RR Lyrae stars and Type 1a supernova. The standard candle used differs based on the distance to the source we are observing. Distances to relatively close galaxies are ...


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I can show you an ESA Series exercise I did a few months ago for an astronomy class. Given the light curve of 12 cepheid variable stars in the galaxy M100 (which are very nice standard candles to measure large distances): We can find the distance between us and the M100, a spiral galaxy in the Virgo cluster, using the apparent magnitude m and the absolute ...


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