Talk:Stellar parallax

Footnotes

It's a minor point, but footnote 23 to chapter 2 of Helge Kragh's 2007 book Conceptions of Cosmos states that the Scottish astronomer Thomas Henderson was in fact the first person to fully calculate a measurement of stellar parallax (for Alpha Centauri). However, Henderson's measurement was published after Bessel's. Something like the previous line could be added to the main text, or the wording of the last line of the introduction changed to read: "The first published measurement of stellar parallax was made by Friedrich Bessel..." Robk78 (talk) 00:07, 19 March 2011 (UTC)

To be factually correct, F.G.W. Struve measured the distance of Vega before than Bessel of 61 Cygni. It is even a published fact, see e.g. publication in Astronomische Nachrichten 1837 (vol 14): https://articles.adsabs.harvard.edu//full/1837AN.....14..249S/0000131.000.html

Bessel published his results about a year later in 1838 in Monthly Notices of Royal Astronomical Society (NB! see: https://articles.adsabs.harvard.edu//full/1838MNRAS...4..152B/0000152.000.html , end of the first page where Bessel credits Struve). Bessel presented of course a very neat analysis (in the case of Struve, all the observations and analysis is published IMHO in publications of Tartu/Dorpat observatory).

Now the real question is, was Henderson even earlier.

IMHO Struve should be properly credited, what do you think? Tonisee (talk) 16:24, 8 August 2022 (UTC)

To reply by myself:

Henderson did his measurements few years before Struve (1832-33), but did not publish them until 1840.

Struve did his first published measurements in 1835-1836, published 1837

Bessel did his first published measurements in 1837-1838, published 1838 Tonisee (talk) 18:04, 8 August 2022 (UTC)

Vega#Observational history has an interesting description of this. Probably we could write something similar in this article. Lithopsian (talk) 18:52, 8 August 2022 (UTC)

distance up to 10.000 is possible

Nasa claims that the "Hubble Space Telescope, astronomers now can precisely measure the distance of stars up to 10,000 light-years". http://www.nasa.gov/press/2014/april/nasas-hubble-extends-stellar-tape-measure-10-times-farther-into-space/#.VhZ_Byud6zM I'm not good enough in english, so someone else has to include that into the article ;) 217.7.244.33 (talk) 14:38, 8 October 2015 (UTC)

Other uses of the term "parallax"

I am not a scientist, but my understanding is that the word "parallax" is used by astronomers in an extended sense to mean "distance measurement", no matter what the method, in particular when the method has nothing to do with geometry. If so, wouldn't it be nice to mention that explicitly when introducing these other kinds of "parallax"? TomS TDotO (talk) 12:34, 17 December 2015 (UTC)

Note reference to Cosmic Distance Ladder GenacGenac (talk) 18:08, 24 July 2017 (UTC)

 Done - Rod57 (talk) 12:45, 4 November 2021 (UTC)

Calandrelli

Apparently, Calandrelli reported a parallax of 4.4 arc seconds for Vega, which is clearly too large - it would represent a distance of less than a quarter of a parsec, less than a light year. How should this be reported here? I suggest that we say something like, "there were reports of the detection of the parallax before Bessell, such as Giuseppe Calandrelli in about 1806 claimed an annual parallax of Vega of more than 4 arc seconds." TomS TDotO (talk) 02:35, 12 January 2016 (UTC)

Secular scales - motion of the sun

The motion of the Sun through space provides a longer baseline that will increase the accuracy of parallax measurements, known as secular parallax. For stars in the Milky Way disk, this corresponds to a mean baseline of 4 AU per year, whereas for halo stars the baseline is 40 AU per year.

Why the discrete difference? —Tamfang (talk) 22:30, 31 January 2017 (UTC)

I had the same question. ... Looking at Local standard of rest (LSR) and Solar apex perhaps the 40 AU pa is due to motion along the solar circle of about 255 km/s, and the 4 AU pa applies to nearby stars and is due to the solar peculiar motion (relative to the LSR) of about 20 km/s (towards the solar apex)? - Rod57 (talk)

Exquisite

I am informed that "exquisite" is often said of a parallax. I suggest that that usage be explained. TomS TDotO (talk) 22:02, 2 February 2017 (UTC)

It is used in the sense of its Oxford English Dictionary definition: "Carefully ascertained or adjusted; accurate, exact." An example is "The exquisite parallaxes obtained from the Hipparcos mission suggest a resolution to puzzling gaps seen in the main sequence of field populations and clusters."

References

StarryGrandma (talk) 20:07, 24 July 2017 (UTC)

Trigonometric parallax

Why isn't the term "trigonometric parallax" in this article?

All it says is: "Once a star's parallax is known, its distance from Earth can be computed trigonometrically."

It is oddly defined under Visual binary as :

Trigonometric parallax

In order to use this method of calculating distance, two measurements are made of a star, one each at opposite sides of the Earth's orbit about the Sun. The star's position relative to the more distant background stars will appear displaced. The distance, $d$ is found from the following equation,

$d={\frac {1AU}{\tan(p)}}$

Where $p$ is the parallax, measured in units of arc-seconds.[1]

[1] As referenced to Martin Harwit, "Astrophysical Concepts" isbn = 0-387-94943-7 publisher = Springer

The general topic is the part of the basis of astrometry, and the origin of the unit of measure known as the parsec. Here, back in 2008, is was reirected here[1] but it seemed no one cottoned onto this absolutely shocking error here. Arianewiki1 (talk) 08:24, 12 June 2019 (UTC)

I suggest completely renaming the article. It is entirely about the trigonometric (geometric) parallax method, as applied to stars, and directs readers elsewhere for different "parallax" methods for measuring stellar distances (none of which are strictly parallaxes, but that's what they're called). Note Parallax (disambiguation) which correctly identifies what this article is about, although using the adjective geometric rather than trigonometric. Lithopsian (talk) 17:31, 12 June 2019 (UTC)

Or if it is too greedy to hog trigonometric parallax purely for astronomy, merge the other types of stellar parallax into this article, with much of the current content as a trigonometric parallax section. Lithopsian (talk) 18:53, 12 June 2019 (UTC)

How is milliarc sec more precise than microarc sec

It says "Very long baseline interferometry in the radio band can produce images with angular resolutions of about 1 milliarcsecond, and hence, for bright radio sources, the precision of parallax measurements made in the radio can easily exceed those of optical telescopes like Gaia." whereas it reports the Gaia data as 10-40 micro-arc secs. - Rod57 (talk) 12:52, 4 November 2021 (UTC)