<p>I would use <a href="https://ssd.jpl.nasa.gov/horizons.cgi" rel="nofollow noreferrer">JPL Horizons</a> to calculate the position of the Moon and save the results to a text file. Then use a spreadsheet to calculate the separation between the Moon and your object. <span class="math-container">$$\cos \theta = \sin \delta_1 \sin \delta_2 + \cos \delta_1 \cos \delta_2 \cos (\alpha_1 - \alpha_2)$$</span> where <span class="math-container">$\theta$</span> is the separation, <span class="math-container">$\delta$</span> is the declination, and <span class="math-container">$\alpha$</span> is the right ascension.</p>

<p>Since the Moon moves about 1 degree in 2 hours, you can use that to determine what time interval to use in the output, depending on how accurately you want to find the 30 degree separation. </p>

CC BY-SA 4.0
2018-09-27T17:01:24.087Z
2018-09-27T17:01:24.087Z
JohnHoltz
<p>Not a tool, but you could try looking at an Astronomical Almanac - for example, the
2019-2023 Astronomical Almanac by Richard Bartlett lists daily moon RA and Dec values in the PDF version, which may meet your needs - here's a link to the free early PDF:</p>

<p><a href="https://www.dropbox.com/s/smm2eprodpod0cf/2019-2023%20Astronomical%20Almanac%20%28Free%20Early%20PDF%29.pdf?dl=0" rel="nofollow noreferrer">https://www.dropbox.com/s/smm2eprodpod0cf/2019-2023%20Astronomical%20Almanac%20%28Free%20Early%20PDF%29.pdf?dl=0</a></p>

<p>Free to share, but if you find it useful the author asks you to consider buying a copy and/or leaving a review.</p>

CC BY-SA 4.0
2018-09-26T23:32:28.700Z
2018-09-26T23:39:46.990Z
2018-09-26T23:39:46.990Z
JerryTheC
<p>I'm planning an observation for a proposal and I need to determine which dates the moon is within 30 degrees of an object so I can ask to not be scheduled for those dates.  This object is near the ecliptic so it is guaranteed the moon will pass close by at times.</p>

<p>In the past I've used skycalc to manually figure out such dates, but now I need to figure out dates over a several month period, and I was hoping there was some more automated tool I could use for this purpose.</p>

CC BY-SA 4.0
2018-09-26T23:27:48.927Z
How precise do you need to be? I would guess that "within 30 degrees" is just an estimate. Therefore, you can find one time interval and add 27.322 days to it (the mean sidereal period) to find future dates with reasonable precision.
JohnHoltz
CC BY-SA 4.0
2018-09-27T00:11:17.327Z
30 degrees is a selected but hard boundary.
NeutronStar
<observational-astronomy>
Planning observation: determine dates where moon is within 30 degrees of my object?
NeutronStar
# Planning observation: determine dates where moon is within 30 degrees of my object?

(Asked by: username_0 on 2018-09-26)

I'm planning an observation for a proposal and I need to determine which dates the moon is within 30 degrees of an object so I can ask to not be scheduled for those dates. This object is near the ecliptic so it is guaranteed the moon will pass close by at times.

In the past I've used skycalc to manually figure out such dates, but now I need to figure out dates over a several month period, and I was hoping there was some more automated tool I could use for this purpose.

**Tags:** observational-astronomy

> **Comments:**
> **username_1**: How precise do you need to be? I would guess that "within 30 degrees" is just an estimate. Therefore, you can find one time interval and add 27.322 days to it (the mean sidereal period) to find future dates with reasonable precision.  
> **username_0**: 30 degrees is a selected but hard boundary.  

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## 2 answers

### Answer by username_1 on 2018-09-27. Score: 1 | Accepted answer

I would use [JPL Horizons](https://ssd.jpl.nasa.gov/horizons.cgi) to calculate the position of the Moon and save the results to a text file. Then use a spreadsheet to calculate the separation between the Moon and your object. $$\cos \theta = \sin \delta\_1 \sin \delta\_2 + \cos \delta\_1 \cos \delta\_2 \cos (\alpha\_1 - \alpha\_2)$$ where $\theta$ is the separation, $\delta$ is the declination, and $\alpha$ is the right ascension.

Since the Moon moves about 1 degree in 2 hours, you can use that to determine what time interval to use in the output, depending on how accurately you want to find the 30 degree separation.


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### Answer by username_2 on 2018-09-26. Score: 0

Not a tool, but you could try looking at an Astronomical Almanac - for example, the
2019-2023 Astronomical Almanac by Richard Bartlett lists daily moon RA and Dec values in the PDF version, which may meet your needs - here's a link to the free early PDF:

<https://www.dropbox.com/s/smm2eprodpod0cf/2019-2023%20Astronomical%20Almanac%20%28Free%20Early%20PDF%29.pdf?dl=0>

Free to share, but if you find it useful the author asks you to consider buying a copy and/or leaving a review.


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