Moon drift calculation (conspiracy theory!)

[Tmh556]

Hi,

I have a really random question. I just watched “The Moon Revealed. It’s a hollow space ship” on The Why Files on YouTube which is a very unique take on the moon. Anyway, in the video it states that the moon almost perfectly covers the sun in a lunar eclipse but due to lunar recession (the moon moving away from the earth at a rate of 1.5 inches per year) it no longer fully covers the sun. My question is what year in the past did the moon fully cover the sun.

[Graham Darke]

The Moon still fully covers the Sun presently during an eclipse, well usually anyway. The Moon’s orbit around the Earth is not perfectly circular so at certain times of the month the Moon is either closer or further away from Earth than its average distance. The variation in distance between the Moon’s closest point and farthest point from Earth is 26,500 miles approximately. If the Moon Earth and Sun align at a point when the Moon is closer then the Moon’s apparent diameter as seen from Earth is greater and fully covers the Sun during a total Solar eclipse. If on the other hand an eclipse occurs when the Moon is further from Earth then the Moon’s apparent diameter may not completely cover the Sun and we have what’s called an annular eclipse. If that happens then the Moon only covers the central part of the Sun, as seen from Earth, leaving a ring of fire. Whether we get a total or annular eclipse depends entirely on where the Moon is in its orbit around the Earth when the nodes align. Very occasionally we get something called a hybrid eclipse where the Moon’s apparent diameter is only great enough during some  of the eclipse to completely cover the Sun and for remainder of the event we have an annular eclipse.
 

The Moon is indeed receding from Earth at a leisurely 4 cm per year so at some point in the very distant future it won’t have sufficient apparent diameter to fully cover the Sun during an eclipse. Right now that doesn’t happen however. 

[vlaiv]

To further expand:

https://en.wikipedia.org/wiki/Solar_eclipse

(it has nice info on both lunar and solar apparent size depending on current orbital position and how they relate)

[robin_astro]

3 hours ago, Graham Darke said:

If on the other hand an eclipse occurs when the Moon is further from Earth then the Moon’s apparent diameter may not completely cover the Sun and we have what’s called an annular eclipse.

 So according to this link this first occurred about 1.6 billion years ago, the first time the sun did not completely cover the sun during (an otherwise) total solar eclipse

https://public.nrao.edu/ask/when-did-the-first-annular-eclipse-occur/

Robin

Edited March 24 by robin_astro
clarity

[Mr H in Yorkshire]

The current Astronomy Now magazine has a good article on exactly this topic.

[Tmh556]

Thanks for all that. Interesting to mull over having known next to nothing about this a day ago. :)

[Paul M]

Due to the Earth/Moon tidal interaction. The Earth slowly dissipates rotational energy to the Moon's orbital energy. 

Therefore the Earth's axial rotation gradually slows and the Monn gets further away. There will be a time in the disant futer when the Moon won't ever be large enough in the sky to cover the Sun, in any eclipse circumstances.

The dinisaurs lived in an era of much shorter days and there were no annular solar eclipses.

 

[robin_astro]

On 24/03/2024 at 18:11, Paul M said:

The dinisaurs lived in an era of much shorter days and there were no annular solar eclipses.

Hi Paul,

Do you have a reference for that?  According to the reference I posted above, annular eclipses first started happening about 1.6 billion years ago, well before the dinosaurs. There are a lot of uncertainties in the calculation though

 

Cheers

Robin

[robin_astro]

15 minutes ago, robin_astro said:

There are a lot of uncertainties in the calculation though

The information in this link might form the basis for an alternative calculation of when the first annular eclipse occurred

https://www.quora.com/How-long-was-a-day-during-the-dinosaurs

Robin

[Paul M]

12 hours ago, robin_astro said:

Do you have a reference for that?

It lurks in the depths of my decaying grey matter   I first read that, without getting further references, a long time ago. Perhaps from "Asimovs Guide to Science". The only metric I remember is that at one time an Earth day was only 18 hours long. That is probably the primordial Earth?

Your Quora reference was a surprise to me, but more current and reliable than my 45+ year old memory of the subject! I am now inclined to re-visit the this. I'd have thought that tidal friction would be precicley known nowadays and calculated without use of fossil records. But then again, continental drift and sea level change will make it a non-linear change over such a large timescale.

Leave it with me....