r/todayilearned • u/LakeM0bius_hunter • 10h ago

TIL that the Moon moves about 3.8 centimetres farther away from Earth every year.

https://science.nasa.gov/moon/facts/?utm_source=chatgpt.com
146 Upvotes

95% Upvoted

55 comments sorted by

62

u/danius353 9h ago

The hugely cool part of this is that right now the sun is 400 times wider than the moon but also 400 times further away from Earth. This is why we can get totality during solar eclipses which is incredibly cool.

Due to the moon’s drift away from Earth at some point of time, the moon will look noticeably smaller than the sun and total eclipses will no longer exist. Similarly, some time ago, the moon was too close and appeared larger than the sun, completely blocking the sun during eclipses.

We are lucky to live in the Goldilocks period for total solar eclipses

28

u/ballofplasmaupthesky 9h ago

We live on the planetary equivalent of a winning powerball ticket.

-14

u/Greene_Mr 7h ago

But don't say it's 'cause a deity did it...

6

u/Double-decker_trams 8h ago

This is why we can get totality during solar eclipses which is incredibly cool.

We would get totality way more often if the Moon appeared larger than the Sun in the sky though. We are in the Goldilocks period for partial solar eclipses, not total. I mean.. Jupiter gets solar eclipses constantly. Even multiple times a day. Because four Moons appear larger than the Sun in Jupiter's sky. And a very small axial tilt. For example Io causes a solar eclipse ever 1.8 days (every orbit).

And the size the Moon appears in Earth's sky is roughly the same as the Sun on average. ~378 is the more exact ratio on average, not 400. So on average the Moon actually appears slightly smaller than the Sun. But since Earth around the Sun and the Moon around Earth orbit elliptically (not a perfect circle), the size it appears can vary.

7

u/manondorf 7h ago

we'd get totality, but not the coolest part of it, which is seeing the corona around the shadow of the moon. If the moon were too close, it would block that too.

3

u/Double-decker_trams 7h ago

Yeah. That's not what the previous commentator wrote though.

1

u/shrimpcest 7h ago

It would have just been easier for you to write, "I just want to argue semantics rather than actually provide anything substantive to the conversation"

2

u/aztronut 2h ago

This particular Goldilocks period for TSEs is actually 54-60% of the Earth's existence, so not that lucky really.

2

u/Dakens2021 8h ago

I think the cool part is eventually if allowed to continue the Moon will get to a point where it reaches equilibrium with the Earth and since the Moon is gaining angular momentum from the Earth they will then eventually both become completely tidally locked to each other. This may not happen before the sun goes red giant and destroys both of them though.

1

u/BKS_ELITE 8h ago

What is tidally locked and if it happened today what would it look like?

2

u/Dakens2021 8h ago

It basically means the Earth and Moon would be locked together so one side of the Earth would always face the same side of the Moon. Right now the Moon shows roughly the same side to the Earth always, with libration it's a little over 50% and you never see the far side of the Moon. When tidally locked the far side of Earth would never see the Moon. The climate of the Earth would change a lot, and the tides would be less extreme on Earth. The Moon also would be much farther away from the Earth than it is now.

1

u/BKS_ELITE 5h ago

Thank you!

2

u/MisinformedGenius 8h ago

The Moon is currently tidally locked to the Earth, which means its rotation period is the same as its orbital period. In practical terms, this means you're always seeing the same side of the Moon when you look in the sky.

However, that's not true when looking from the Moon - the Earth rotates. Over a very very long period of time, likely longer than the Earth's lifetime, the Earth will slow its rotation (due to the same force that causes the tides) until its rotation period becomes the same as the Moon's orbital period. So whenever you look in the sky from Earth, you see the same side of the Moon, and whenever you look in the sky from the Moon, you see the same side of Earth.

2

u/BKS_ELITE 5h ago

Thank you so much, I really appreciate it /u/MisinformedGenius

2

u/aztronut 2h ago

This is the current situation with Pluto and Charon.

1

u/aztronut 2h ago

The eventual equilibrium point would take 50 billion years to reach and there's only another 5 billion years until the Sun engulfs us.

1

u/TriggerHydrant 8h ago

Sydney 2028, I’m planning on going!

1

u/LazyFurry0 7h ago

I genuinely believe that besides the whole life and civilization thing, Earth’s perfect eclipses are what it would most be remembered for in the universe. That’s got to be such a rare thing

1

u/AssumptionAcceptable 6h ago

Its very close, not exactly 400 time wide and further, okay

1

u/nowhereman136 3h ago

The unique size and distance of the sun and moon makes Earth very special in the known universe. In the future, Aliens may come to Earth to experience a solar eclipse since they don't have that on their planets... Maybe they already have

0

u/Greene_Mr 7h ago

This means eclipses in the distant past must've been fucking TERRIFYING :-O

1

u/aztronut 2h ago

TSEs in the far distant past would have been much more dramatic than today's. At formation, the Moon orbited at roughly 3.8 Earth radii (~24,000 km from Earth's center, or about 18,000 km above the surface). At that distance its angular diameter would have been roughly 8°, about 15 times the Sun's ~0.53°. So totality was guaranteed every time the Moon crossed the Sun and the umbral shadow would have been enormous, and the path of totality would have spanned a huge fraction of the planet's surface. Annular eclipses were simply not a possibility.

-1

u/hyperfoxeye 5h ago

I mean the moon was just 250 feet closer at 0 AD

1

u/Greene_Mr 5h ago

I said DISTANT past... 0 AD is hardly that.

1

u/hyperfoxeye 4h ago edited 4h ago

Okay if you wanna go that route then at a million years earth was 23.61 miles closer while still being 238000 miles away.

At a billion years ago its sizably different at 23612 miles closer, or roughly 10% larger in the sky. Definitely terrifyingly big

46

u/reepobob 9h ago

I thought it looked farther away lately. Now I know why.

11

u/banjodoctor 9h ago

Wait until you’re older.

2

u/lluciferusllamas 9h ago

Is that accelerating or decelerating?

2

u/Ok-Worker5125 9h ago

It’s both

2

u/MisinformedGenius 8h ago

Decelerating. The Moon will eventually stop moving away from the Earth.

1

u/lluciferusllamas 6h ago

Which means eventually the moon will crash into earth? 

1

u/MisinformedGenius 5h ago

No, it will stop moving away and stay at its same altitude. It is gaining altitude right now basically because the Earth rotates faster than it. Its rotation is tugging on the Moon, making the Moon move slightly faster and making the Earth rotate slightly slower. Eventually the Earth will rotate at exactly the same rate that the Moon orbits, so that process will stop.

If the Moon and the Earth were the only things in the universe, they would technically radiate away orbital energy through gravitational waves until they crashed into each other, but this is an extraordinarily slow process, around 1020 years, so something else would happen to them long before that.

1

u/aztronut 2h ago

The current rate is anomalously high, it's boosted by ocean tidal resonance tied to present-day continental configurations. The rate will decline as the continents shift and the oceans eventually evaporate.

0

u/ApisTeana 9h ago

Yes

1

u/lluciferusllamas 6h ago

So is it accelerating its deceleration, or decelerating its acceleration? 

1

u/Phenxz 9h ago

I knew it!

3

u/kernald31 9h ago

So that's why we haven't been able to send humans back to the moon, it's too far now!

3

u/varnell_hill 9h ago

Earth is ghetto so it doesn’t want to be near us.

1

u/badmrbones 8h ago

The Distance of the Moon by Calvino is one of my favorites.

1

u/edingerc 7h ago

The Moon is trying to get away so astronauts don't leave any more bags of poop on its surface.

1

u/AmphibianSure4877 7h ago

Not if I have anything to do with it

•

u/drfunk 8m ago

So, a penis length?

0

u/Discount_Friendly 9h ago

Who can blame him

-1

u/Aldo-D-D-Wilson 9h ago

That's scary

1

u/armaedes 8h ago

Scarier if it was moving closer every year.

1

u/LolYouFuckingLoser 7h ago

Dawn of the Final Day

0

u/FightinRndTheWorld 8h ago

I can't blame it.

0

u/-Words-Words-Words- 8h ago

Come back Moon! Come back!

0

u/wartopuk 7h ago

oh hey look.. another 21 day old account hiding its history with something posted to death here.

0

u/happy2harris 5h ago

This is why we haven’t been to the moon since the Apollo missions. It was easier back then. 

0

u/tallulahgi 4h ago

Even the moon is trying to get away from the shit show that is our world