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Author Topic: Stars  (Read 749 times)

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Michkov

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Re: Stars
« Reply #12 on: January 19, 2019, 03:57:30 PM »

As far as stars go you can throw away thing apparent magnitude below 6.5, 7 if you like round numbers. Keep in mind with magnitudes it's lower value brighter objects (a full moon is -12, the brightest stars -1) and it's non linear in real brightness due to how our eyes work.

In good approximation stars are black bodies, for any divergence you'd really need to look at the spectrum. So look for the effective temperature (could be just temperature) listed with the star and plug that into a black body color calculator. You should be able to compute this once and keep it static, star color doesn't change over such short timescales we are using here.
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Stainless

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Re: Stars
« Reply #13 on: January 20, 2019, 05:00:59 AM »

Yes and that is what confuses me.

Sirius has an apparent visual magnitude of -1.46, yet the LOWEST value I have in this catalogue is 0.46.

That's just wrong. It implies that all the really bright stars, the one's we really want for navigation, are missing from the database. Sigh.

So I have found a new database, I am going to have to parse that and see what that looks like.
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Michkov

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Re: Stars
« Reply #14 on: January 21, 2019, 09:45:57 AM »

Have you got an id next to the 0.46mag star it strikes me as a odd that the brightest ones are not in the database.

This one here lets you query various catalogues. I set the link to the Harvard you've been using thus far and checked Sirius is in there with a V_mag of -1.46 which matches the accepted literature value for it.
http://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=V/50/catalog&-out.max=unlimited&-out.form=HTML%20Table&-out.add=_r&-out.add=_RAJ,_DEJ&-sort=_r&-oc.form=sexa

Sadly the Harvard catalogue has no effective temperature column. I'd list the spectral classification and match the various classes to temperature thus apparent colour.

EDIT: I think I figured out where you get the -0.46 from. There are only 3 instances of the number in the catalogue and the only one near magnitude is in the B-V column. The B-V, similar U-V are magnitude differences for magnitudes measured in different wavelength. This gives two classification parameters for astronomers, not really relevant for what you want. You want V_mag and SpType(there only the Capital letter numeral part), plus the coordinates ofc.
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Stainless

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Re: Stars
« Reply #15 on: January 23, 2019, 09:53:27 AM »

I figured it out.

I looked in an online database for Sirius and got it's Henry Draper catalogue number.

I then looked in my data for that star, and sure enough it was there with an apparent visual magnitude of -1.4.

I noticed that it is marked as an IR source, I was assuming IR sources are not visible, wrong assumption.
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