<p>Observation. There are many pictures on the internet showing both stars, but the pair have been "visually" observed for decades. For example, see below from <a href="http://iopscience.iop.org/article/10.3847/1538-4357/aa6af8/meta" rel="nofollow noreferrer">Bond et al. (2017)</a>. </p>

<p>As you can see, the accuracy of visual observers was poor, especially near minimum separation where the separation was over-estimated, but HST observations have nailed the orbit, allowing a precise mass determination.</p>

<p>Note that if only one star is observed then precise mass estimates cannot be obtained (think about Kepler's third law).</p>

<p>This image also answers your other question(s) about Sirius.</p>

<p><a href="https://i.sstatic.net/Y3C2z.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Y3C2z.jpg" alt="The orbit of Sirius AB"></a></p>

CC BY-SA 4.0
2018-10-24T12:27:21.807Z
are images close to apastron in the public domain?
user24634
CC BY-SA 4.0
2018-10-24T16:34:59.110Z
@user24634 The HST images are certainly public domain. How you would get hold of scans of the photographic measurements from the 60s and 70s, I don't know. Perhaps ask Howard Bond?
ProfRob
CC BY-SA 4.0
2018-10-24T16:40:24.333Z
are there any images from the apastron accessible online?
user24634
CC BY-SA 4.0
2018-10-24T16:50:13.080Z
@user24634 HST data are available to anyone.
ProfRob
CC BY-SA 4.0
2018-10-24T06:23:38.413Z
2018-10-24T06:23:38.413Z
ProfRob
<p>It is common to base models on deduction rather than empirical observation. The orbit of Sirius A is easily seen as variation in proper motion. The orbit of Sirius B, has it been observed, or is it derived from the orbit of Sirius A (which has empirical data underlying it. )</p>

CC BY-SA 4.0
2018-10-24T05:36:37.977Z
Related: see other questions about Sirius by same user today [here](https://astronomy.stackexchange.com/q/28125/14094) and [here](https://astronomy.stackexchange.com/questions/28124).
Chappo Hasn't Forgotten
<star><data-analysis><orbital-mechanics>
Is the orbit of Sirius B based on observation, or derived from the variation in proper motion of Sirius A?
user24634
# Is the orbit of Sirius B based on observation, or derived from the variation in proper motion of Sirius A?

(Asked by: username_0 on 2018-10-24)

It is common to base models on deduction rather than empirical observation. The orbit of Sirius A is easily seen as variation in proper motion. The orbit of Sirius B, has it been observed, or is it derived from the orbit of Sirius A (which has empirical data underlying it. )

**Tags:** star, data-analysis, orbital-mechanics
> **Comments:**
> **username_1**: Related: see other questions about Sirius by same user today [here](https://astronomy.stackexchange.com/q/28125/14094) and [here](https://astronomy.stackexchange.com/questions/28124).  

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## 1 answers

### Answer by username_2 on 2018-10-24. Score: 1

Observation. There are many pictures on the internet showing both stars, but the pair have been "visually" observed for decades. For example, see below from [Bond et al. (2017)](http://iopscience.iop.org/article/10.3847/1538-4357/aa6af8/meta).

As you can see, the accuracy of visual observers was poor, especially near minimum separation where the separation was over-estimated, but HST observations have nailed the orbit, allowing a precise mass determination.

Note that if only one star is observed then precise mass estimates cannot be obtained (think about Kepler's third law).

This image also answers your other question(s) about Sirius.

[![The orbit of Sirius AB](https://i.sstatic.net/Y3C2z.jpg)](https://i.sstatic.net/Y3C2z.jpg)

> **Comments:**
> **username_0**: are images close to apastron in the public domain?  
> **username_2**: @user24634 The HST images are certainly public domain. How you would get hold of scans of the photographic measurements from the 60s and 70s, I don't know. Perhaps ask Howard Bond?  
> **username_0**: are there any images from the apastron accessible online?  
> **username_2**: @user24634 HST data are available to anyone.  

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