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# Star Distance Help Sought

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Hi. Was up at dawn observing Mercury rising in the southeast and slowly swept my binoculars left. I was able to vaguely see a small triangle formed by Upsilon Ophiuchi, HR  6128 and HR 6137. That was the limit of view as sunlight was washing out anything else to the left of that. But I clicked on the adjacent HR6144 star in my Sky Guide app and it lists as being 6,900 light years away. When I checked the Ski Safari app, the same star is listed as 1,900 light years. I went online and found little info but, “In the Sky” web page it’s HR 6144 at 9 kilo years / 9,000 light years. Does anyone have any info as to why the huge discrepancies?

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Stellarium has it at about 4500 ly.

Apparently, its  spectral type is A9 II/III, somewhere in the giant to bright giant range. It may be difficult to pin down its precise absolute brightness, which of course has a bearing on its distance.

http://simbad.u-strasbg.fr/simbad/sim-id?Ident=HR++6144 call it a post asymptotic giant branch star and a proto planetary nebula.

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Ruud, thanks very much for the concise explanation. All those numbers at Simbad make my head orbit.

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From Gaia the parallax is 0.3612 mas

To find the distance in parsecs divide 1 by the parallax in arcsecs.

For this star it will be 1/.0003612 = 2768 parsecs
A parsec is 3.26 light years so this star is about 9000light years distant.

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2 hours ago, wxsatuser said:

From Gaia the parallax is 0.3612 mas

To find the distance in parsecs divide 1 by the parallax in arcsecs.

For this star it will be 1/.0003612 = 2768 parsecs
A parsec is 3.26 light years so this star is about 9000light years distant.

The parallax error in DR2 is +/- 0.0557, so the star's distance is between about 7,800 and 10,700 light-years. I believe these small parallaxes (large distances) are not so reliable in this data release.

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The parallax error in DR2 is +/- 0.0557, so it's distance is between about 7,800 and 10,700 light-years. I believe these small parallaxes (large distances) are not so reliable in this data release.

Yes, just showing an example so the op can see if the quoted distances are close or not.

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