Stellarium

Where are stellar distances coming from?

Asked by Josh Lake

I do a lab with my astronomy classes that involves looking up star distances in Stellarium and comparing them to Wolfram Alpha. These often match just fine, but sometimes they are radically different.

For instance, look at HIP 87150. Stellarium has it 862.85 ly, converts to 264.4 pc. This squares with the parallax angle: 1/0.00378" = 264 ly.

However, Wolfram Alpha has it at 2468 ly, 756.7 pc: http://www.wolframalpha.com/input/?i=HIP+87150

Wikipedia nearly agrees at 2470 ly: http://en.wikipedia.org/wiki/List_of_stars_in_Ophiuchus

I can understand a bit of a difference, but what catalog or source is Stellarium pulling the distance data from? Is it being calculated with the parallax angle? Or is it from a list?

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Alexander Wolf (alexwolf) said : 		#1

Stellarium calculates distance to stars via parallax data, which get from Hipparcos catalog.

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Josh Lake (4-rootlake) said : 		#2

Thanks Alexander Wolf, that solved my question.

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Josh Lake (4-rootlake) said : 		#3

In that case, can I somehow check values from a catalog file? My example of HIP 87150 doesn't match up.

From the main catalog, it says 1.32 ma, 0.00132" : http://apm5.ast.cam.ac.uk/cgi-bin/wdb/hipp/hipparcos/query

This squares with Wolfram Alpha, Wikipedia, etc.

From Stellarium, it reads as 0.00378". Is there a way to check Stellarium's catalog? Or is it hard-coded into the program?

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Josh Lake (4-rootlake) said : 		#4

I just searched for HIP 87150 in this page: http://archive.ast.cam.ac.uk/hipp/hipparcos.html

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Alexander Wolf (alexwolf) said : 		#5

http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=HIP+87150&submit=SIMBAD+search

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Josh Lake (4-rootlake) said : 		#6

Ah, I see. So to summarize:

Stellarium uses the new reduction of the Hipparcos catalog, updated for accuracy in 2007.

Wolfram Alpha and other sources must be pulling values from the original HIP catalog, before this new reduction.

Do you think this is accurate?

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Alexander Wolf (alexwolf) said : 		#7

Yes, new reduction is more accurate.

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Josh Lake (4-rootlake) said : 		#8

I think I will contact the Wolfram Alpha team and/or Wikipedia editors and see if the new reduction can be added to the given info. Thanks!