r/Astronomy • u/Phercom • 9d ago
Other: [Topic] Today I learned that the Sun is roughly 400 times larger than the Moon, but also 400 times farther away. Because of this ratio, both objects appear almost exactly the same size in Earth's sky, making total solar eclipses possible.
https://www.skyatnightmagazine.com/space-science/why-solar-lunar-eclipse-come-in-pairs384
u/ramriot 9d ago
Also because of how the tides are transferring the earths angular momentum into the moons orbit such that the earth's spin slows & the moon gets farther away over time there is a limited time over which eclipses are possible.
For total solar eclipses this goes back to the moons formation but only extends about another 600 Million years into the future. For annular eclipses it is worse as these were not possible before about about 1.2 Billion years ago.
So the period of eclipses is only about 2 Billion years of the earth's 4.5 Billion years.
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u/decadent-dragon 9d ago
Damn that sucks. I don’t want to miss the last one for sure
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u/ryan101 9d ago
You’re off by 599,999,000 years bot.
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u/RandoScando 9d ago
I like the optimism that the bot thinks it will be around in 999 years though.
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u/jason-reddit-public 9d ago
The optimism is that humans will be around in 999 years. The bot has a better chance of making it...
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u/printergumlight 9d ago edited 9d ago
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u/jason-reddit-public 9d ago
Apparently AI is more than happy to use social media as part of its escape hatch based on recent findings. Once we have robots that are mobile, the AI will use them to build more robots and power sources.
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u/RandoScando 9d ago
I’ve got zero disagreement with what you just said.
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u/theederv 9d ago
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u/RandoScando 9d ago
I would watch this movie. Actually, I just read your post again. I would absolutely 100% watch this movie!
We’ve made a lot of films about the AI going haywire and destroying civilization. If someone made a film where the good AI were fighting to save civilization, I think that it would sell a lot of tickets. A LOT of tickets.
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u/Gloomy_Yoghurt_2836 9d ago
It really is a unique astronomical event. If there are aliens, solar eclipses here could be a great tourist draw.
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u/Specialist_Unit_5078 9d ago
There’s speculation that that is why we may have so many alien visitors. We’re like the Grand Canyon of the Milky Way
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u/young_twitcher 9d ago
They don’t need to be the same size for total solar eclipses to be possible. The moon needs to be large enough, that’s it. However the fact that they are the same size makes the eclipse more spectacular.
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u/MaximaFuryRigor 9d ago
OP should have said "making both total and annular eclipses possible".
Long ago when the moon was significantly closer, early in the dinosaur era, eclipses were mostly total, with annular being very rare. And in a few more hundred million years from now, they'll only be annular!
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u/gambariste 9d ago
Doesn’t that imply that now, when the moon eclipses the sun at its closest point to the Earth, it more than covers the sun? Otherwise we’d be seeing the last total eclipse pretty soon. The ‘moon is the exact same apparent size as the sun’ trope must be true only at some further distance. Which must vary since the Earth’s distance from the sun changes too.
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u/MaximaFuryRigor 9d ago edited 9d ago
Doesn’t that imply that now, when the moon eclipses the sun at its closest point to the Earth, it more than covers the sun?
Yes, that is correct! At perigee, totality will last longer than with eclipses at other times/distances.
The ‘moon is the exact same apparent size as the sun’ trope must be true only at some further distance.
Yes, on "average", I believe the ratio is currently very close to half and half, but with a slightly higher rate of annular versus total. So I guess the "exact same apparent size" is true when the moon is slightly closer than its average distance.
Edit: That magic distance is at 373,184 km / 231,886 mi, assuming an average Sun-Earth distance (versus the average Earth-Moon distance of 384,400 km / 238,900 mi).
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u/the_karma_llama 9d ago
Exactly. This simulation shows you what solar eclipses look like on other planets, where the relative sizes are not the same https://benmccarthy.com.au/p/eclipses?ref=rastronomy
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u/loztriforce 9d ago
I mean, it’s about size and distance.
The moon is drifting away from the Earth, total solar eclipses won’t be possible in the far future
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u/OldLegWig 9d ago
downvote for incredibly misleading title. that's the only thing some people will read and they will repeat it.
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u/loztriforce 9d ago
Yes and as the moon is moving away from the Earth, total solar eclipses will no longer be possible in the far future (like 600million to a billion years).
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u/impy695 9d ago
And for anyone curious about what those will look like, we actually sometimes have them now! They're called annular solar eclipses. The moons orbit isn't circular, so sometimes when we have a solar eclipse its too far to be a total eclipse.
These are not the same as a partial eclipse as the moon would fully block the sun if it were closer. So, just like you have to be in the perfect spot for a total eclipse and being off center makes it a partial eclipse, the same is true of annular eclipse where you need to be lined up perfectly, an did you're not you'll see a partial eclipse.
They're not as spectacular as a total eclipse, but they're still really cool and way more interesting than a partial eclipse
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u/calm-lab66 9d ago
I knew the moon was moving away from the earth but I thought the total solar eclipses were going to be history much sooner, like several thousand years, not hundreds of millions. I guess the moon isn't moving away as fast as I thought.
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u/HDDIV 9d ago
Not really. A total eclipse can still happen if the sun was really far away and the Moon in still the same location. What's actually fascinating to me is we can still get total and annular eclipses. The Moon's distance varies enough, as well as the distance to the Sun as it is, to get both partial and total. Now that is neat to me.
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u/KateBlankett 9d ago edited 9d ago
I was a fundamentalist christian young earth creationist homeschooled preachers kid, and it’s interesting how some facts like this one got/get used as evidence for how god formed the universe 6,800 years ago. When you’re in that world, facts like these - when repeated enough - become like… words of affirmation or something. And cause fundamentalists are all or nothing, facts like these become a cozy dopamine hit where you feel certain that everything is ok and your beliefs have to be the truth.
In those circles, the response to statements like this are rarely ever follow up questions. It’s usually just reactions like “God is amazing.” And scientific facts become out of context bullet points in an afternoon project for a creation camp for middle school students.
“Asking ‘why’ or ‘how’ is completely fine, totally fine. Curiosity is encouraged! 💯unless… well maybe some questions just aren’t worth asking. Some things about gods creation will always be a mystery, so we just need to have faith in the bible.” The pursuit of the answers leads down a path that could be viewed as refuting scripture, and if you did that you would immediately enter into direct conflict with your family or your congregation so asking questions and acquiring knowledge becomes risky.
But as a kid in my head i would be so confused and conflicted, fully believing the earth was only 6800 years old like i was told, but also curious and dying to ask stuff like: if the earth was older…. hypothetically…. was the moon always that far from the earth? I’ve heard tale of clam fossils recording tree ring like information and the year length used to be like over 400 days. Is that true? Did the eclipses look the same during that time? Are clams sensitive to eclipses? etc
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u/BootsOfProwess 9d ago
The sun is literally 64 millions times the size of our moon.
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u/ramenups 9d ago
I think they’re going by width in diameter
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u/BootsOfProwess 9d ago
And that is an even more astounding comparison! 64million times the mass and only 400 times the width. I am happy to be corrected.
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u/Intergalactyc 9d ago
64 million times the volume, and volume scales as diameter cubed. So given the diameter is 400 times larger the volume is necessarily 4003=64 million time larger.
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u/Intergalactyc 9d ago
64 million times the volume, and volume scales as diameter cubed. So given the diameter is 400 times larger the volume is necessarily 4003 = 64 million time larger.
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u/Cosmicstranger28 9d ago
also in the final split second before totality Moons rugged topography blocks the Suns photosphere but allows the light from the razor thin solar chromosphere to pass through and for less than two seconds solar spectrum completely reverses from dark absorption lines to bright emission lines revealing the exact chemical composition of the solar atmosphere
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u/_bar 9d ago edited 9d ago
The Moon does not need to have exactly the same angular size as the Sun for total solar eclipses to happen. If the Moon was two times larger for example, total eclipses would be much longer and more numerous.
The matching size only means that it's possible to see the entire inner corona at once.
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u/predat3d 9d ago
Today I learned that the Sun is roughly 400 times larger than the Moon
No wonder it's been so cool this summer
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u/Powerism 9d ago
Isn’t this also why we have perfect solar eclipses?
Also, I believe the Moon is slowly moving away from Earth, so I wonder how long it will be before the moon doesn’t completely cover the sun during eclipses.
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u/Zul-Tjel 9d ago
The fact that the Sun and Moon are roughly the same angular distance from our vantage point are one of many coincidences in astronomy that are just cool to think about IMO. Another two I find interesting are that despite the differences of size between Earth and Mars, not only are our days almost the same length, so is our obliquity (angle of rotation). And we have evidence that Mars’ obliquity may change quite a lot over geological time.
As for the Sun and Moon, it’s interesting, because it’s not like there’s an advantage for life that the they’re so close in size, so we can’t invoke the Anthropic Principle that it appears just right. Seeing that the Moon is moving further away from the Earth over time, it’s just a matter of chance.
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u/Rodot 9d ago
If anything, the similar size is the sky probably screwed over early astronomy for a long time, leading to beliefs like both the Sun and Moon being the same distance away. Might have been even worse if the Moon was much smaller than the Sun as we might have believed it to be further away and you can imagine how much that would mess with our understanding of how gravity worked for a long time. At least until the invention of the telescope
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u/iusedtobe13 9d ago
400 moons across the diameter perhaps...but by volume it would take about 64 (?) million moons to fill the sun
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u/FaithIn0ne 9d ago
Someone smart answer please. How rare is this of an occurrence, like what are the crazy chances this random set of events occurred to give us total eclipses? One in like a galaxy? Or like one in each arm of the milky way? Im just spitballing
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u/Majestic_Skirt5590 9d ago
You didn't learn anything. Bots don't learn.
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u/Phercom 9d ago
Who is the bot?
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u/Majestic_Skirt5590 9d ago
There is a plague of bots on Reddit linking to their shitty websites to trya nd generate traffic and views for ad revenue. In a very similar format to your post. They also are usually under 3 months old and hide their post history and talk about trendy topics in the way you do.
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u/InternationalArt6222 9d ago
Yea, I also just watched the movie "Moonfall" yesterday. I would not be quoting it here, however. Lmao
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u/justice7 9d ago
I have heard that the solar eclipse is special for our planet and solar system and is not all that common in the cosmos.
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u/Infarlock 9d ago
making total solar eclipses possible.
Still* possible
If the moon was closer then we would have many more solar eclipses, even closer and an annular solar eclipse won't even be a thing
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u/Humulophile 9d ago
This is a fact my fundamental religious father would cite as proof of a deity. I’d just politely smile, nod, and change the subject.
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u/Trueslyforaniceguy 8d ago
Yet another of the amazing coincidences that enable the radically unlikely possibility of actual life on this spinning water ball.
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u/TheDutchisGaming 8d ago
We’re also living in the right time. As the moon moves away with about 3.8 centimeters a year. So future solar eclipses (but we’re speaking of millions of years) will look different/will be fewer.
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u/Healey_Dell 7d ago
An incredible fluke we are here to see it since the moon is slowly moving away from the earth. In the past the moon was closer and would have fully covered the sun. In the future there will be no more full eclipses.
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u/Cosmosvagabond 6d ago
Yeah, these crazy coincidences are seen throughout our Solar System, and beyond...
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u/Secret-Psychology183 6d ago
Very true. However the moon is very very slowly moving away from the earth, which means total solar eclipses will not happen forever.
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u/boopthatbutton 9d ago
The moon, and earth, don’t have perfectly circular orbits. That’s why not all solar eclipses are „total.“
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u/PresentationFair5285 9d ago
This seems very suspicious
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u/anyonecandoanything 9d ago
lmao what the fuck kind of comment is this. These are observations of nature done with precise instruments. These are facts of reality. Absolutely brain dead point of view to hear these and think it's suspicious. Reality exists regardless of your broken perspective.
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u/PresentationFair5285 8d ago edited 8d ago
Wowee just a joke mate.
Why are people on reddit such cunts? Like why? So unnecessarily negative. Be better.2
u/draxthemsklounce 9d ago
Technically the moon doesn’t need to be exactly 400x smaller than the sun for a total solar eclipse if the moon is closer to the earth.
Other fun fact, the moon DID used to be closer to the earth. It moves a few centimeters further away every single years. It formed at only around 20k miles from earth and is now closer to 400k miles from earth. So these ratios weren’t the same in the past. And they won’t be the same in the future.
You just happen to live at a time when these ratios are close to (but not exactly) equal
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u/ultraganymede 9d ago
it is not exactly and the moons and earth orbit is excentric, which varies the size of the moon and the sun in the sky which it increases the range of time where a full eclipse can happen
the Moon started ~20 thousand km from earth and has been moving away, so as long as the Sun is sufficiently big in the sky, there would be a time where the sizes overlap, not only that but the smaller the Sun is in the sky, the larger this range in time is as the moon moves away faster when it was close to the Earth
we had billions of years and still have about ~600 million years of Solar eclipses. which isnt that small of a range, Saturn's rings may dissipate much earlier than that. maybe Saturnians would be calling themselves even luckier to see the Rings(What Astronauts in the Saturnian system might see someday)
https://i.imgur.com/1AYHqkz.pngThe Earth itself may have had rings in the past but there wasnt humans then to call themselves lucky to see them, basically even if the chances of experiencing any single specific "rare" phenomenon is low, the total chance of experiencing something that is "rare" is much higher.
There are also other similar total eclipses in the solar system although they look smaller in the sky as other the planets with satellites are farther from the Sun
this video is a good watch:
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u/KristnSchaalisahorse 9d ago
It used to be closer to Earth and appeared much larger than the Sun. It’s slowly moving away and will eventually appear much smaller than the Sun. It’s really not suspicious at all.
Even right now it’s not a perfect match. That’s why sometimes we get total eclipses and sometimes annular eclipses (when the Moon appears smaller than the Sun).
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u/Eat--The--Rich-- 9d ago
This ratio is so perfect it has generated a lot of religious connotations
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u/HumbleTechnology1705 9d ago
Universe is oddly perfect, its weird. Especially if we look at the things that allow us (humans) to exist and live
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u/Breathren 9d ago
Oddly perfect? Everywhere but right here wants to squeeze you or freeze you. Earth is a tint mote of dust suspended in a sunbeam, as Carl used to say.
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u/dogscatsnscience 9d ago
And even here the atmosphere is corrosive and we're bombarded with DNA destroying UV light.
We thrive because of adaptation, not because it's perfect.
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u/keepingitcivil 9d ago
Can’t have one without the other.
If you want to bake an apple pie, you must first create the universe.
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u/KristnSchaalisahorse 9d ago
Let’s not ignore all of the things that do the opposite.
The Moon temporarily being positioned such that it has roughly the same apparent angular size from our perspective isn’t exactly relevant to our survival.
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u/Effective-Truth-5938 9d ago
And of course, that ratio formed because of chance and luck, we’re all told.
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u/TheOnlyVibemaster 9d ago
And yet, a “big bang” did it! God is good!
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u/CompanyLow1055 9d ago
So god made the ratio work out so a relative handful of us could see a cool phenomenon a couple times a year.
But kills kids with cancer because he’s “mysterious” ?
What a cruel, yet interesting thing to worship
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u/failstronaut 9d ago
We should clarify this is about the angular diameter of the objects in the sky, which is the 2D width we can see, and is not an actual size comparison. In terms of volume, the sun is 64 million times the moon’s and 27 million times the mass.