Talk:Astronomical unit
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Since the NIST Guide in the links uses "ua" as the symbol for this unit, and the IAU Style Manual in the links uses "au" as the symbol for this unit, why does this article use a different symbol, "AU"?
Why doesn't it at least mention those other symbols? Gene Nygaard 03:35, 17 Dec 2004 (UTC)
- In practice, "AU" or "au" is universal. Using "ua" would cause no end of confusion. The IAU is the authority for astronomy.
- As for whether to use AU or au, it seems that Astronomy magazine uses "AU" and Sky and Telescope uses "a.u." (!) So as they say, "go figure". -- Curps 21:41, 26 Dec 2004 (UTC)
- One reason why it may be suitable for ua (and why the above guide uses ua) is the international country code for Australia is au, causing confusion. But, as said previously, AU is most used. So that's how it stands.
Taylor 08:27, 3 August 2005 (UTC)
removed Francophobic comments re: the Bureau des Poids et Mesures, and replaced it with the more neutral explanation.
I came across a web-page that show the best AU is different from 149 597 870 691 ± 30 metres.
The address list below. And the contents show between two lines. http://www.scenta.co.uk/tcaep/nonxml/science/constant/details/Astronomical%20Unit.htm
| Name | Astronomical Unit |
| Symbol | AU |
| Value | 1.495 978 706 60 ± 0.000 000 000 20 × 1011 m |
| Category | Astrophysical |
| Comments | The astronomical unit is defined as the mean distance between the Earth and the Sun.
The mean distance between the centre of mass of the Sun and the centre of mass of the Earth-Moon system is 1.000 0023 AU. The best measurement of the astronomical unit comes from phase-modulated continuous-wave radio signals reflected off other planets. It was continuous-wave signals returned from the Viking probes on Mars that allowed the determination of the astronomical unit to 20m. |
YuWong yuwong36@yahoo.com
- Do you know how to read scientific notation? The values are the same, except the one at your link is 30 m less, and it’s ±20 instead of 30. It’s an imperceptible difference, really (unless you do it for a living). —Frungi 04:57, 25 February 2006 (UTC)
[edit] How did they do it in ancient times
How did people measure the distance of the sun from the earth accurately in ancient times? Does anyone know? —The preceding unsigned comment was added by 81.179.39.220 (talk • contribs) 13:51, 19 January 2006 (UTC).
- In ancient times, people didn’t believe in the solar system. Except for Galileo, which was why they ganged up on him. —Frungi 04:14, 25 February 2006 (UTC)
Well, not really. Ancient Greeks did know how to calculate the distance of the Sun from the Earth (they already knew that the Earth revolves around the Sun). They also knew that the Earth was round and they knew how to calculate its diameter. Aristarchus of Samos, who lived circa 310 BC - 230 BC used a method for determining the Earth-Sun distance, which had to do with measuring the angle in the sky between the Sun and the Moon when it is precisely in its first quarter phase. This was a particularly difficult thing to measure accuratly at that time. You would also have to know the Earth-Moon distance (which he did) to perform the calculation. Even though his measures weren't extremely accurate, the model was correct. And it's quite impressive that a man, some 2200 years ago, without telescopes, instruments or even a calculator, actually managed to find out how far away the Sun is. Leschatz 15:17, 5 March 2006 (UTC)
Message regarding "acceptance" of the value I edited here:
The value I wrote in for
"AU = 149 597 870 696.0 +/- 0.146"
is from Russia, figured from their ephemeris called "EPM2004" (of 2004). The newest NASA value (figured using their ephemeris called "DE410" of 2003) is
"AU = 149 597 870 697.4 +/- 0.3"
which is do to work headed by Myles Standish of the JPL. Both values were presented at the IAU Colloquium 196. In the transcript of the discussions between the Russians and Myles Standish at that meeting, the Russians tell him his value has a uncertainty of "1.4" ( and thus by implication, that their value is better). He said "perhaps the extra digit they have is significant, I am not sure".
Thus I choose to use the Russian value for the AU.
Sincerely, EGB
[edit] astronomical units
how long does it take to travel one astronomical unit in measures of time (minutes, hours, days, months, etc.) ??????????????? —The preceding unsigned comment was added by 71.168.192.207 (talk) 00:19, 6 March 2007 (UTC).
