<p>TL;DR version, Yes, yes, distortion. In more detail:</p>

<ol>
<li>HST's orbit is approx. 90 minutes so this will cause the breaks. Some more information is given in the <a href="https://hst-docs.stsci.edu/display/HSP/HST+Cycle+27+Primer+Orbital+Constraints" rel="noreferrer">Orbital Constraints</a> section of the Cycle 27 guide for proposers.</li>
<li>Since HST is having to move to track the moving comet to keep it in the (small) field of view of the instruments, it will likely need to roll the spacecraft. This is to keep suitable guide stars in the Fine Guidance Sensors, to keep the Sun on the solar panels for power and to keep the pointing constraints of not looking to close to the Sun, Moon or Earth satisfied. These are discussed in more detail in the <a href="https://hst-docs.stsci.edu/display/HSP/HST+Cycle+27+Primer+Pointing%2C+Orientation%2C+and+Roll+Constraints" rel="noreferrer">Orientation and Roll constraints</a> section of the primer/guide for proposers mentioned earlier.</li>
<li>This is due to the geometric distortion of the optics in UV/Visible (UVIS) channel of the WFC3 instrument as described in more detail in this <a href="https://hst-docs.stsci.edu/display/WFC3IHB/6.4+UVIS+Field+Geometry" rel="noreferrer">section of the WFC3 Instrument Handbook</a>,</li>
</ol>

CC BY-SA 4.0
2019-10-17T22:07:24.040Z
ASTRO*nomy questions answered in a* SNAP *with zero* E*rror* R*ate!* Thanks for answering three questions in one.
uhoh
CC BY-SA 4.0
2019-10-17T17:03:39.483Z
2019-10-17T17:03:39.483Z
astrosnapper
<p><a href="https://i.sstatic.net/KSBxs.gif" rel="nofollow noreferrer"><img src="https://i.sstatic.net/KSBxs.gif" alt="enter image description here"></a></p>

<p>This GIF is made (via giphy.com) from the new NASA Goddard video <a href="https://youtu.be/JG9x6tkf8mg" rel="nofollow noreferrer">Hubble's New Image of Interstellar Object</a> and if I understand correctly many (if not all) of these frames are from <a href="https://archive.stsci.edu/proposal_search.php?mission=hst&amp;id=16009" rel="nofollow noreferrer">https://archive.stsci.edu/proposal_search.php?mission=hst&amp;id=16009</a> (from <a href="https://astronomy.stackexchange.com/a/33695/7982">this answer</a>).</p>

<p>I have some questions about this set of images. I've plotted the start times below.</p>

<ol>
<li>There are four groups that last about 45 minutes, each followed by a break of either 45 minutes or 90+45 minutes, is this related to the HST's orbit? </li>
<li>I notice a slow rotation of the star tracks over the duration of the roughly seven hours of data, it looks like roughly 20 degrees, (see GIF or the individual images) and I can't figure that out at all. Is it a rotation of the HST around its own axis?</li>
<li>Individual <em>preview</em> images (<a href="https://archive.stsci.edu/cgi-bin/mastpreview?mission=hst&amp;dataid=IE6K01U3Q" rel="nofollow noreferrer">example</a>) appear to be rhomboidal rather than square, why?</li>
</ol>

<p><a href="https://i.sstatic.net/xsQaz.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/xsQaz.png" alt="enter image description here"></a></p>

CC BY-SA 4.0
2019-10-17T14:29:38.233Z
related: [Which are stars and which are noise in this comet photo?](https://astronomy.stackexchange.com/q/33681/7982)
uhoh
<photography><comets><hubble-telescope>
Questions about Hubble's brand new view of an interstellar comet (video)
uhoh
# Questions about Hubble's brand new view of an interstellar comet (video)

(Asked by: username_0 on 2019-10-17)

[![enter image description here](https://i.sstatic.net/KSBxs.gif)](https://i.sstatic.net/KSBxs.gif)

This GIF is made (via giphy.com) from the new NASA Goddard video [Hubble's New Image of Interstellar Object](https://youtu.be/JG9x6tkf8mg) and if I understand correctly many (if not all) of these frames are from <https://archive.stsci.edu/proposal_search.php?mission=hst&id=16009> (from [this answer](https://astronomy.stackexchange.com/a/33695/7982)).

I have some questions about this set of images. I've plotted the start times below.

1. There are four groups that last about 45 minutes, each followed by a break of either 45 minutes or 90+45 minutes, is this related to the HST's orbit?
2. I notice a slow rotation of the star tracks over the duration of the roughly seven hours of data, it looks like roughly 20 degrees, (see GIF or the individual images) and I can't figure that out at all. Is it a rotation of the HST around its own axis?
3. Individual *preview* images ([example](https://archive.stsci.edu/cgi-bin/mastpreview?mission=hst&dataid=IE6K01U3Q)) appear to be rhomboidal rather than square, why?

[![enter image description here](https://i.sstatic.net/xsQaz.png)](https://i.sstatic.net/xsQaz.png)

**Tags:** photography, comets, hubble-telescope

> **Comments:**
> **username_0**: related: [Which are stars and which are noise in this comet photo?](https://astronomy.stackexchange.com/q/33681/7982)  

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## 1 answers

### Answer by username_1 on 2019-10-17. Score: 5 | Accepted answer

TL;DR version, Yes, yes, distortion. In more detail:

1. HST's orbit is approx. 90 minutes so this will cause the breaks. Some more information is given in the [Orbital Constraints](https://hst-docs.stsci.edu/display/HSP/HST+Cycle+27+Primer+Orbital+Constraints) section of the Cycle 27 guide for proposers.
2. Since HST is having to move to track the moving comet to keep it in the (small) field of view of the instruments, it will likely need to roll the spacecraft. This is to keep suitable guide stars in the Fine Guidance Sensors, to keep the Sun on the solar panels for power and to keep the pointing constraints of not looking to close to the Sun, Moon or Earth satisfied. These are discussed in more detail in the [Orientation and Roll constraints](https://hst-docs.stsci.edu/display/HSP/HST+Cycle+27+Primer+Pointing%2C+Orientation%2C+and+Roll+Constraints) section of the primer/guide for proposers mentioned earlier.
3. This is due to the geometric distortion of the optics in UV/Visible (UVIS) channel of the WFC3 instrument as described in more detail in this [section of the WFC3 Instrument Handbook](https://hst-docs.stsci.edu/display/WFC3IHB/6.4+UVIS+Field+Geometry),

> **Comments:**
> **username_0**: ASTRO*nomy questions answered in a* SNAP *with zero* E*rror* R*ate!* Thanks for answering three questions in one.  

---

