Measuring Lunar Distance: A do it yourself guide

[LaydeeDem]

Hi all. Hopefully this doesn't count as self-promotion but I recently had the opportunity to do a lunar parallax experiment with fellow KSPF member @cubinator. We measured the Mun's Moon's parallactic displacement against the star Theta Lyrae. After some spreadsheet wrangling and triple checking my math, I finally feel confident enough to share our results;

 

Between my location in New Mexico and Cubinator's location in Minnesota, we measured a lunar parallax of ~283.6 arcseconds. This gave us a topocentric lunar distance of 390,775.4 km from cubinator's location and a topocentric lunar distance of 389,366.3 km from my location. Checking against the actual values given by the astronomy program Stellarium shows we have a percent error of only 0.42%!

 

I've written up an article on Medium detailing the full methodology and the math that went into this here: https://medium.com/@DeeAlexandria/how-to-measure-the-distance-to-the-moon-a1e502440918

 

Please feel free to give it a read and some feedback! Cheers.

[Scotius]

Now, if you could repeat your observations in collaboration with an established YouTuber. It would be a nice counter to the many moronic videos posted by flat Earthers about Moon being only a light under the glass dome, and hovering only couple of thousands of kilometers above the surface of their fantasy pancake world

[LaydeeDem]

4 hours ago, Scotius said:

Now, if you could repeat your observations in collaboration with an established YouTuber. It would be a nice counter to the many moronic videos posted by flat Earthers about Moon being only a light under the glass dome, and hovering only couple of thousands of kilometers above the surface of their fantasy pancake world

Semi-popular youtube debunk channel VoysovReason follows me on Twitter. Maybe something will come from that. Or maybe Scott Manley will see it somehow! (I can dream can't I?) I would make a video myself but I'm quite insecure about my voice.

[YNM]

6 hours ago, Scotius said:

flat Earthers

They even refuse to admit the Earth has a radius and a center (not surface).

7 hours ago, Nutt007 said:

Between my location in New Mexico and Cubinator's location in Minnesota...

I pretty much live on the opposite side of the Earth from you (on the east hemisphere and south of the equator), maybe we can get a better result ?

Granted I don't have a telescope with me now ! But I know some others who do...

[cubinator]

1 hour ago, YNM said:

I pretty much live on the opposite side of the Earth from you (on the east hemisphere and south of the equator), maybe we can get a better result ?

No, because you can't look at the Moon at the same time.

1 hour ago, YNM said:

opposite side of the Earth

 

[HebaruSan]

11 hours ago, Nutt007 said:

Checking against the actual values given by the astronomy program Stellarium shows we have a percent error of only 0.42%!

Now you just need to learn to write clickbait headlines.

"Moon surges 0.42% closer, recent study finds"

[YNM]

5 hours ago, cubinator said:

No, because you can't look at the Moon at the same time. 

If I have a clear horizon then yes I can.

The great circle distance between my place and any point in New Mexico is around 140 degrees away (maxes out at 142 degrees). The difference in longitude is only 150 degrees.

But "clear horizon" and "place where I live" isn't very synonymous...

Edited September 25, 2018 by YNM

[Superfluous J]

8 minutes ago, YNM said:

If I have a clear horizon then yes I can.

The great circle distance between my place and any point in New Mexico is around 140 degrees away (maxes out at 142 degrees).

But "clear horizon" and "place where I live" isn't very synonymous...

The problem is, you'll both be at sunrise/sunset or one of you will be observing during the day. This will make measuring anything in the sky that much harder, and stars even more so. Also, atmospheric refraction will cause issues though I don't know how bad that is offhand.

[YNM]

5 minutes ago, 5thHorseman said:

The problem is, you'll both be at sunrise/sunset or one of you will be observing during the day.

Today would actually be perfect since we're very close to the equinoxes and the moon is full.

But then a full moon is very bright...

Yeah, I guess it's not as perfect as it can be thought of !

[LaydeeDem]

15 hours ago, YNM said:

Today would actually be perfect since we're very close to the equinoxes and the moon is full.

But then a full moon is very bright...

Yeah, I guess it's not as perfect as it can be thought of !

It would definitely simplify the math. The triangle between us and the Moon would essentially be isosceles. Refraction, skyglow and moonglow would be an issue and my Western horizon is nothing but mountains. We'd have to use a decently bright star as well given the moonglow. It's raining tonight but we could try next full Moon on the 24th of October. The brightest stars in the field will be 73 Ceti and 65 Ceti, both at magnitude ~4.3. The November full Moon will be even better. The Moon comes within a few degrees of bright star Aldebaran which is magnitude 0.85.

Edited September 26, 2018 by Nutt007

[YNM]

38 minutes ago, Nutt007 said:

The Moon comes within a few degrees of bright star Aldebaran which is magnitude 0.85. 

Well, I don't have any DSLR with me, so... yeah.

Also, here on November I'd be swamped by rainclouds.

Edited September 26, 2018 by YNM

[ChrisSpace]

So I just tried a slightly different method, using the angular size and known diameter of the moon instead, and as of exactly 12 hours ago I got a distance of 382000 +- 1000 kilometres. How close did I get?

[LaydeeDem]

1 hour ago, ChrisSpace said:

So I just tried a slightly different method, using the angular size and known diameter of the moon instead, and as of exactly 12 hours ago I got a distance of 382000 +- 1000 kilometres. How close did I get?

That depends largely on your location on Earth relative to the Moon, the position of the Moon in its elliptical orbit and the accuracy of your angular size measurement. I'd say you're well within the ballpark though.

[mikegarrison]

Maybe it's just me, but when I want to know how far away the moon is, I go to Wikipedia. Just last week it told me the moon was 200 meters away, and if you read it on the Internet, you know its true.