<p>I'm working on some software which needs to calculate the position of stars and galaxies visible to the naked eye at different periods of human history.</p>

<p>The <a href="http://tdc-www.harvard.edu/catalogs/bsc5.html" rel="nofollow noreferrer">Yale Bright Star Catalogue</a> gives the position and proper motion of visible stars.</p>

<p>Is calculating the historic positions simply a matter of multiplying each stars proper motion by the number of years between the date in question and the epoch, then subtracting the result from the position?</p>

<p>If so how far back in history could one go with this method and still produce a map that resembles what a human would observe with the naked eye? Would this method alone be sufficient to go back as far as 5000 years or are the other factors in play here that would need to be accounted for to make this accurate?</p>

<p>My criteria for "accurate" here is that a human observer wouldn't see a noticeable difference between the map and the night sky with the naked eye. Smaller inaccuracies are tolerable.</p>

CC BY-SA 4.0
2019-10-15T16:40:34.267Z
61 Cyg A is the naked eye star with largest p.m. moving ~7.3deg in 5000 yrs; most will be much less. I think you might be better with the [Hipparcos & Tycho](http://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=I/239/hip_main) for the proper motions as they should be more accurate than YBS. A general issue will be the error on the proper motion (which is mas/yr) is often a large fraction of the measured value so this will be a big effect if you extrapolate 5000 years. Also this is ~20% of the ~26,000 precessional cycle of the pole so you will likely want to include that
astrosnapper
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2019-10-15T20:14:00.403Z
@astrosnapper That looks more like an answer than a comment... ;)
PM 2Ring
CC BY-SA 4.0
2019-10-15T21:03:07.660Z
@astrosnapper: That is now outdated information, as already with Gaia data realease 2 (DR2) the astrometric precision is higher than what the TGAS stars had.
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-10-15T21:56:32.040Z
@AtmosphericPrisonEscape was going to mention Gaia as it's normally the "go-to" but the OP specifically mentioned bright, naked eye stars. From what I remember there were still some residual issues with the gated mode on Gaia fro very bright stars so Hipparcos may still be better... ?
astrosnapper
CC BY-SA 4.0
2019-10-15T22:23:06.720Z
@astrosnapper: I'll ask around about that issue tomorrow in the institute with the people working on Gaia, but we were recently chatting about this and the consensus was that the Tycho-Gaia astrometric solution is now superfluous.
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-10-18T18:26:03.533Z
@astrosnapper Also bare in mind that 5.000 years ago some stars with high proper motion that are dimmer than naked eye visibility could have been naked eye visible then. A case for 70.000 years ago: https://en.wikipedia.org/wiki/Scholz%27s_Star
Swike
CC BY-SA 4.0
2019-10-19T16:12:49.447Z
@astrosnapper thank you for this information. This field is new to me so I'm learning lots from these comments. I will look into other catalogues for greater precision. Is the PM error quoted in any catalogue so i can at least understand how much I'm dealing with? Also, you mention the precessional cycle.. in my case I'm only interested in how the stars positions have changes in relation to other stars, not the earth (for example does a constellation look different). Do you say I may need to account for it because the precession will cause parallax, moving the stars in relation to each other?
John
CC BY-SA 4.0
2019-10-19T16:38:08.317Z
@Swike that's a good point. My goal is to understand what factors I should account for to be able to see what a constellation would have looked like 5000 years ago. Based on the comments I have: Proper motion, possibly the precessional cycle if the parallax effect changes relative positions of stars, and the change in brightness. Is the rate of change in brightness sufficiently well know and predictable as to be able to calculate how bright a star would have been at a given point in history?
John
<star-maps>
Calculating historical star maps from proper motion
John
# Calculating historical star maps from proper motion

(Asked by: username_0 on 2019-10-15)

I'm working on some software which needs to calculate the position of stars and galaxies visible to the naked eye at different periods of human history.

The [Yale Bright Star Catalogue](http://tdc-www.harvard.edu/catalogs/bsc5.html) gives the position and proper motion of visible stars.

Is calculating the historic positions simply a matter of multiplying each stars proper motion by the number of years between the date in question and the epoch, then subtracting the result from the position?

If so how far back in history could one go with this method and still produce a map that resembles what a human would observe with the naked eye? Would this method alone be sufficient to go back as far as 5000 years or are the other factors in play here that would need to be accounted for to make this accurate?

My criteria for "accurate" here is that a human observer wouldn't see a noticeable difference between the map and the night sky with the naked eye. Smaller inaccuracies are tolerable.

**Tags:** star-maps

> **Comments:**
> **username_1**: 61 Cyg A is the naked eye star with largest p.m. moving ~7.3deg in 5000 yrs; most will be much less. I think you might be better with the [Hipparcos & Tycho](http://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=I/239/hip_main) for the proper motions as they should be more accurate than YBS. A general issue will be the error on the proper motion (which is mas/yr) is often a large fraction of the measured value so this will be a big effect if you extrapolate 5000 years. Also this is ~20% of the ~26,000 precessional cycle of the pole so you will likely want to include that  
> **username_2**: @username_1 That looks more like an answer than a comment... ;)  
> **username_3**: @username_1: That is now outdated information, as already with Gaia data realease 2 (DR2) the astrometric precision is higher than what the TGAS stars had.  
> **username_1**: @username_3 was going to mention Gaia as it's normally the "go-to" but the OP specifically mentioned bright, naked eye stars. From what I remember there were still some residual issues with the gated mode on Gaia fro very bright stars so Hipparcos may still be better... ?  
> **username_3**: @username_1: I'll ask around about that issue tomorrow in the institute with the people working on Gaia, but we were recently chatting about this and the consensus was that the Tycho-Gaia astrometric solution is now superfluous.  
> **username_4**: @username_1 Also bare in mind that 5.000 years ago some stars with high proper motion that are dimmer than naked eye visibility could have been naked eye visible then. A case for 70.000 years ago: https://en.wikipedia.org/wiki/Scholz%27s_Star  
> **username_0**: @username_1 thank you for this information. This field is new to me so I'm learning lots from these comments. I will look into other catalogues for greater precision. Is the PM error quoted in any catalogue so i can at least understand how much I'm dealing with? Also, you mention the precessional cycle.. in my case I'm only interested in how the stars positions have changes in relation to other stars, not the earth (for example does a constellation look different). Do you say I may need to account for it because the precession will cause parallax, moving the stars in relation to each other?  
> **username_0**: @username_4 that's a good point. My goal is to understand what factors I should account for to be able to see what a constellation would have looked like 5000 years ago. Based on the comments I have: Proper motion, possibly the precessional cycle if the parallax effect changes relative positions of stars, and the change in brightness. Is the rate of change in brightness sufficiently well know and predictable as to be able to calculate how bright a star would have been at a given point in history?  

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## 0 answers

