<p>Narrow field telescopes such as HST or JWST are basically never randomly pointed - the field of view and density of interesting objects is not high enough that this would be viable and such a proposal would never make it out of the Time Allocation Committee as a valid use of precious and expensive telescope time.</p>
<p>Looking at page 586 (&quot;ASTRO-13&quot;) of the <a href="https://www.nasa.gov/sites/default/files/atoms/files/fy23_nasa_budget_request_full_opt.pdf" rel="noreferrer">NASA FY23 Budget Request</a> we can see that Hubble and JWST are \$98.3 and \$187 million a year to operate (I took the FY24 numbers as a &quot;steady state&quot; for JWST). From a <a href="https://www.stsci.edu/files/live/sites/www/files/home/hst/about/space-telescope-users-committee/presentations-and-documentation/_documents/2022_may/hstmo.pdf" rel="noreferrer">report</a> to the Space Telescope User Committee, we can find that Hubble executes about 75 orbits (each ~95 minutes) of observations per week in recent Cycles, making the cost per orbit about \$25k or about \$16k/hour to operate. I don't have similar numbers for JWST and being out at L2 makes operations a little easier, but it's also newer and operations won't be as streamlined as they are for Hubble, but given the budgets, we can assume ~2x Hubble so \$32k/hour.</p>
<p>Oversubscription rates vary by cycle, science program category and instrument but approx. people ask for four times as much time on Hubble as is available and the selection rate for proposals is about 20%. So 80% of the people who apply with detailed science and observing plans for what they want to do get nothing and no observing time. Given this oversubscription rate, if you propose to randomly point the telescope and have no idea what you're going to see and whether it will produce anything to justify the time spent, your proposal will get a very low grade and zero time awarded.</p>
<p>Blind/random discovery is not the job of precision instruments such as HST or JWST; that's what sky surveys are for. These will tile a substantial fraction of the sky with an instrument that has a large field of view in a single exposure, usually in only 1 or maybe 2 filters and often for a specific science goals such as discovering Near Earth Objects (e.g. <a href="https://fallingstar.com/home.php" rel="noreferrer">ATLAS</a>) or supernovae/explosive transients (e.g. <a href="https://ztf.caltech.edu" rel="noreferrer">ZTF</a> or <a href="https://asas-sn.osu.edu/" rel="noreferrer">ASAS-SN</a>) but can also be a general purpose survey with a variety of science goals (e.g. <a href="https://www.sdss.org" rel="noreferrer">Sloan Digital Sky Survey (SDSS)</a>). These surveys will find large numbers of new examples of known objects which weren't their primary science goal (e.g. new eclipsing binaries found in the OGLE survey for microlensing events <a href="https://ui.adsabs.harvard.edu/abs/1994AcA....44..317U/abstract" rel="noreferrer">Udalski et al. 1994</a>. Occasionally, entirely new classes of object will be found of which the most famous example is <a href="https://en.wikipedia.org/wiki/Hanny%27s_Voorwerp" rel="noreferrer">Hanny's Voorwerp</a> found in Galaxy Zoo images. These new objects or a subset e.g. &quot;we'll pick the 10 best eclipsing binary candidates from our survey for further study&quot; can then be studied in detail using larger 4-8m telescopes or space assets like HST and JWST.</p>
<p>This model of &quot;small widefield telescope finding interesting objects for big telescopes&quot; dates back to the original 48&quot;/1.2m <a href="http://sites.astro.caltech.edu/palomar/about/telescopes/oschin.html" rel="noreferrer">Samuel Oschin Schmidt</a> and the <a href="http://skyserver.sdss.org/dr5/en/proj/advanced/skysurveys/poss.asp" rel="noreferrer">Palomar Observatory Sky Survey</a> at Palomar Observatory which surveyed the Northern Sky using photographic plates in two &quot;filters&quot; (emulsions) in part to find and feed interesting targets to the 200&quot;/5m Hale telescope. This was replicated in the Southern Hemisphere with the near-identical <a href="https://aat.anu.edu.au/about-us/uk-schmidt-telescope" rel="noreferrer">UK Schmidt</a> and ESO Schmidt Telescopes and has continued through digital CCD surveys such as SDSS, PanSTARRS and SkyMapper as well as the ATLAS, ZTF and ASAS-SN previously mentioned. This model of &quot;wide and shallow survey first, narrow and deep follow-up later&quot; is more efficient in use of the telescope time and produces a better and higher science return per hour/dollar.</p>
<p>(The closest HST comes to random pointings is the <a href="https://hst-docs.stsci.edu/acsihb/chapter-7-observing-techniques/7-9-parallel-observations" rel="noreferrer">Pure Parallel</a> mode where you can use a different instrument to observe an adjacent field close to where the main prime program and instrument is observing. The pure parallel mode gives you no control over where you look and for how long; that is totally set by the prime program and given the <a href="https://hst-docs.stsci.edu/hsp/the-hubble-space-telescope-primer-for-cycle-30/hst-primer-orbital-constraints" rel="noreferrer">many</a> <a href="https://hst-docs.stsci.edu/hsp/the-hubble-space-telescope-primer-for-cycle-30/hst-primer-pointing-orientation-and-roll-constraints" rel="noreferrer">pointing</a> <a href="https://hst-docs.stsci.edu/hsp/the-hubble-space-telescope-primer-for-cycle-30/hst-primer-observing-considerations" rel="noreferrer">restrictions</a>, the extremely small amount of sky covered by Hubble per year and the types of targets Hubble tends to observe, this is very far from &quot;random&quot; pointings)</p>

CC BY-SA 4.0
2022-10-28T22:40:11.180Z
2022-10-28T22:40:11.180Z
astrosnapper
<p>Recently I happened to be on the MAST portal, looking at jwst data. I happened to come across 2 interesting targets, “random place” and “another random place”</p>
<p>This got me thinking. It’s almost impossible to know what the scientists who pointed jwst at a random place were thinking. However, it’s interesting to think about if this is something that is beneficial, or at least not largely detrimental. It also occurred to me that at some point someone would have to point a telescope at a random point in order to discover things.</p>
<p>So, is pointing telescopes at random places a viable method of doing astronomy, and if so what are examples?</p>

CC BY-SA 4.0
2022-10-26T01:54:21.847Z
Some qualification on what is meant by random would be helpful; if it’s random as in a place where there’s nothing in particular, then this is incredibly viable and is how we got the Hubble deep field images. If it’s random as in using a random number generator to pick a random part of the sky, that’s a different matter.
Justin T
CC BY-SA 4.0
2022-10-26T01:55:13.547Z
@JustinT completely random.
Topcode
CC BY-SA 4.0
2022-10-26T04:06:16.717Z
Not on something like JWST, the time is too valuable, and the likelihood of something interesting landing in the field of view is pretty small.  If JWST does image something "random", it's likely very close to something something else planned.  There are missions specifically designed as "all sky surveys", and the results generally used to find interesting targets.  Even for the Hubble Deep Field, the location was specifically chosen to not be obstructed by local objects.
Greg Miller
CC BY-SA 4.0
2022-10-26T04:15:48.577Z
@GregMiller I mean, I’m just stating what it was named. For all I know it could have been 1000s of hours on selecting those specific areas, and then deciding to call it random.
Topcode
CC BY-SA 4.0
2022-10-26T08:00:36.370Z
One would need to know the observation proposal to judge what kind of random it is. It could be random from a select few places or list of objects.
planetmaker
CC BY-SA 4.0
2022-10-27T05:02:44.363Z
@JustinT the Hubble Deep Field was very carefully selected [paper abstract](https://ui.adsabs.harvard.edu/abs/1996AJ....112.1335W/abstract)  on multiple criteria; it was very far from a random selection.
astrosnapper
CC BY-SA 4.0
2022-10-27T13:02:27.853Z
ISO had to slew from target to target. Given the value of ISO time, data was being taken on swaths of sky between “real” (there’s goalpost-moving) observations.
caInstrument
CC BY-SA 4.0
2022-10-27T20:32:02.953Z
@astrosnapper Very interesting! I did not know that, although I shouldn’t be surprised. The narrative I had always heard was that they decided to point the telescope and a seemingly empty part of the sky and see what happens, and so by the lack of a specific target I considered it ‘random’, but it’s clear from the article that you linked that this was not the case. Very cool!
Justin T
CC BY-SA 4.0
2022-12-27T11:51:39.587Z
It would be helpful if you provided a link to one of these cases. (Then we could see if e.g. the abstract of the observing proposal provided any hints.)
Peter Erwin
CC BY-SA 4.0
2022-12-27T17:45:21.687Z
@PeterErwin the “random place” ones seem to be from proposal 1063
Topcode
CC BY-SA 4.0
2023-03-26T04:57:17.850Z
if anyone happens on this post, by now both random place and another random place have been renamed to their intended targets, which while boring, does clear up this question alot
Topcode
<observational-astronomy><history><james-webb-space-telescope>
Is pointing a telescope at a random place a viable astronomical strategy?
Topcode
# Is pointing a telescope at a random place a viable astronomical strategy?

(Asked by: username_0 on 2022-10-26)

Recently I happened to be on the MAST portal, looking at jwst data. I happened to come across 2 interesting targets, “random place” and “another random place”

This got me thinking. It’s almost impossible to know what the scientists who pointed jwst at a random place were thinking. However, it’s interesting to think about if this is something that is beneficial, or at least not largely detrimental. It also occurred to me that at some point someone would have to point a telescope at a random point in order to discover things.

So, is pointing telescopes at random places a viable method of doing astronomy, and if so what are examples?

**Tags:** observational-astronomy, history, james-webb-space-telescope

> **Comments:**
> **username_1**: Some qualification on what is meant by random would be helpful; if it’s random as in a place where there’s nothing in particular, then this is incredibly viable and is how we got the Hubble deep field images. If it’s random as in using a random number generator to pick a random part of the sky, that’s a different matter.  
> **username_0**: @JustinT completely random.  
> **username_2**: Not on something like JWST, the time is too valuable, and the likelihood of something interesting landing in the field of view is pretty small.  If JWST does image something "random", it's likely very close to something something else planned.  There are missions specifically designed as "all sky surveys", and the results generally used to find interesting targets.  Even for the Hubble Deep Field, the location was specifically chosen to not be obstructed by local objects.  
> **username_0**: @GregMiller I mean, I’m just stating what it was named. For all I know it could have been 1000s of hours on selecting those specific areas, and then deciding to call it random.  
> **username_3**: One would need to know the observation proposal to judge what kind of random it is. It could be random from a select few places or list of objects.  
> **username_4**: @JustinT the Hubble Deep Field was very carefully selected [paper abstract](https://ui.adsabs.harvard.edu/abs/1996AJ....112.1335W/abstract)  on multiple criteria; it was very far from a random selection.  
> **username_5**: ISO had to slew from target to target. Given the value of ISO time, data was being taken on swaths of sky between “real” (there’s goalpost-moving) observations.  
> **username_1**: @username_4 Very interesting! I did not know that, although I shouldn’t be surprised. The narrative I had always heard was that they decided to point the telescope and a seemingly empty part of the sky and see what happens, and so by the lack of a specific target I considered it ‘random’, but it’s clear from the article that you linked that this was not the case. Very cool!  
> **username_6**: It would be helpful if you provided a link to one of these cases. (Then we could see if e.g. the abstract of the observing proposal provided any hints.)  
> **username_0**: @PeterErwin the “random place” ones seem to be from proposal 1063  
> **username_0**: if anyone happens on this post, by now both random place and another random place have been renamed to their intended targets, which while boring, does clear up this question alot  

---

## 1 answers

### Answer by username_4 on 2022-10-28. Score: 8 | Accepted answer

Narrow field telescopes such as HST or JWST are basically never randomly pointed - the field of view and density of interesting objects is not high enough that this would be viable and such a proposal would never make it out of the Time Allocation Committee as a valid use of precious and expensive telescope time.

Looking at page 586 ("ASTRO-13") of the [NASA FY23 Budget Request](https://www.nasa.gov/sites/default/files/atoms/files/fy23_nasa_budget_request_full_opt.pdf) we can see that Hubble and JWST are \$98.3 and \$187 million a year to operate (I took the FY24 numbers as a "steady state" for JWST). From a [report](https://www.stsci.edu/files/live/sites/www/files/home/hst/about/space-telescope-users-committee/presentations-and-documentation/_documents/2022_may/hstmo.pdf) to the Space Telescope User Committee, we can find that Hubble executes about 75 orbits (each ~95 minutes) of observations per week in recent Cycles, making the cost per orbit about \$25k or about \$16k/hour to operate. I don't have similar numbers for JWST and being out at L2 makes operations a little easier, but it's also newer and operations won't be as streamlined as they are for Hubble, but given the budgets, we can assume ~2x Hubble so \$32k/hour.

Oversubscription rates vary by cycle, science program category and instrument but approx. people ask for four times as much time on Hubble as is available and the selection rate for proposals is about 20%. So 80% of the people who apply with detailed science and observing plans for what they want to do get nothing and no observing time. Given this oversubscription rate, if you propose to randomly point the telescope and have no idea what you're going to see and whether it will produce anything to justify the time spent, your proposal will get a very low grade and zero time awarded.

Blind/random discovery is not the job of precision instruments such as HST or JWST; that's what sky surveys are for. These will tile a substantial fraction of the sky with an instrument that has a large field of view in a single exposure, usually in only 1 or maybe 2 filters and often for a specific science goals such as discovering Near Earth Objects (e.g. [ATLAS](https://fallingstar.com/home.php)) or supernovae/explosive transients (e.g. [ZTF](https://ztf.caltech.edu) or [ASAS-SN](https://asas-sn.osu.edu/)) but can also be a general purpose survey with a variety of science goals (e.g. [Sloan Digital Sky Survey (SDSS)](https://www.sdss.org)). These surveys will find large numbers of new examples of known objects which weren't their primary science goal (e.g. new eclipsing binaries found in the OGLE survey for microlensing events [Udalski et al. 1994](https://ui.adsabs.harvard.edu/abs/1994AcA....44..317U/abstract). Occasionally, entirely new classes of object will be found of which the most famous example is [Hanny's Voorwerp](https://en.wikipedia.org/wiki/Hanny%27s_Voorwerp) found in Galaxy Zoo images. These new objects or a subset e.g. "we'll pick the 10 best eclipsing binary candidates from our survey for further study" can then be studied in detail using larger 4-8m telescopes or space assets like HST and JWST.

This model of "small widefield telescope finding interesting objects for big telescopes" dates back to the original 48"/1.2m [Samuel Oschin Schmidt](http://sites.astro.caltech.edu/palomar/about/telescopes/oschin.html) and the [Palomar Observatory Sky Survey](http://skyserver.sdss.org/dr5/en/proj/advanced/skysurveys/poss.asp) at Palomar Observatory which surveyed the Northern Sky using photographic plates in two "filters" (emulsions) in part to find and feed interesting targets to the 200"/5m Hale telescope. This was replicated in the Southern Hemisphere with the near-identical [UK Schmidt](https://aat.anu.edu.au/about-us/uk-schmidt-telescope) and ESO Schmidt Telescopes and has continued through digital CCD surveys such as SDSS, PanSTARRS and SkyMapper as well as the ATLAS, ZTF and ASAS-SN previously mentioned. This model of "wide and shallow survey first, narrow and deep follow-up later" is more efficient in use of the telescope time and produces a better and higher science return per hour/dollar.

(The closest HST comes to random pointings is the [Pure Parallel](https://hst-docs.stsci.edu/acsihb/chapter-7-observing-techniques/7-9-parallel-observations) mode where you can use a different instrument to observe an adjacent field close to where the main prime program and instrument is observing. The pure parallel mode gives you no control over where you look and for how long; that is totally set by the prime program and given the [many](https://hst-docs.stsci.edu/hsp/the-hubble-space-telescope-primer-for-cycle-30/hst-primer-orbital-constraints) [pointing](https://hst-docs.stsci.edu/hsp/the-hubble-space-telescope-primer-for-cycle-30/hst-primer-pointing-orientation-and-roll-constraints) [restrictions](https://hst-docs.stsci.edu/hsp/the-hubble-space-telescope-primer-for-cycle-30/hst-primer-observing-considerations), the extremely small amount of sky covered by Hubble per year and the types of targets Hubble tends to observe, this is very far from "random" pointings)


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