# [FoRK] Astronomy units question

Elias Sinderson elias at cse.ucsc.edu
Thu Apr 14 13:19:07 PDT 2005

```Joe Barrera wrote:

> Eugen Leitl wrote:
>
>>  On Thu, Apr 14, 2005 at 12:49:35PM -0700, Joe Barrera wrote:
>>
>> > What units are they using in this article?
>> > http://www.spaceref.com/news/viewsr.html?pid=16144
>> > The radius of the disk is at least 43" (330 AU), 70" (543 AU), and
>> > 105" (815 AU) in extent at 24, 70 and 160 um, respectively.
>>
>>  AU is astronomical units, I presume
>
> I know what an AU is!!!!  I'm asking what the " is supposed to
> represent.  It sure isn't inches.

Seconds or, more precisely, arc seconds. Degrees are divided into 60 arc
minutes, of 60 arc seconds each. The unit um is, of course, micrometers
- the wavelength the observation was performed at. As they are measuring
the radius of the Vega debris disk at different wavelengths, and the
size of an arc second varies by the distance of the measurement, the AU
figure is an estimate of the size of x" at the distance of the Vega disk
when viewed in a certain wavelength. ...  make sense?

E
```

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