Why Solar Eclipses Create Those Crescent-Shaped Lights

Why Solar Eclipses Create Those Crescent-Shaped Lights


[♪ INTRO] Solar eclipses tend to be pretty big news. The 2017 one in North America was hugely memorable
for millions of people, including the SciShow team. And the 2019 one in South America was equally
amazing and Instagram-worthy. But during those events, the sky isn’t the
only thing people were looking at. They were also fascinated by these crescent-shaped
lights that appeared on the ground, most noticeably underneath trees. The lights are one of the most fun parts of
any solar eclipse, and the science behind them is pretty good, too. The biggest thing causing these lights is
called the pinhole camera effect. Like the name says, it was originally used
to describe pinhole cameras, which work by letting light through a tiny hole in a screen. But the same physics applies when light from an eclipse passes through the spaces between tree leaves. On the most basic level, light comes from
the Sun, passes through those gaps, and then hits a projection surface, usually, the ground. But the important part is that not every ray
of light is able to pass through. The only rays that reach to the ground are
the ones angled in just the right way to make it through the spaces between the leaves. And much of that light takes a very specific
path. It starts from one side the Sun, travels through
the gap in the leaves, and hits the other side of the projection surface. So light that comes from the left side of the Sun ends up on the right side of the patch of ground, and vice versa. This creates an image of the Sun that’s
both upside-down and backwards. And it’s why those little blobs of light look so much like the solar eclipse happening way up in the sky: They’re tiny images of
the eclipse itself. Technically, this means you can observe this
phenomenon regardless of whether an eclipse is happening or not. It’s just that the Sun, without the Moon
in front of it, looks like a circle, so its projected image is just a circle. Pretty nondescript. It’s only once the Moon starts getting in
the way that things become all interesting and pretty. The cool thing about these images isn’t
just their shape, though, it’s also the fact that they’re really crisp and clear. Like, look at these lights compared to the
blobs you normally see underneath trees. The normal lights are fuzzy, while the eclipse
ones are sharp little moon-shaped things. That happens for at least two additional reasons. One is that there’s less ambient light during
an eclipse. Normally, sunlight gets refracted and bounces
around in our upper atmosphere. That gives the sky its nice blue glow, but
that glow is another source of illumination, which makes the lights and shadows we see
pretty fuzzy. As a solar eclipse approaches totality and
the Moon moves completely in front of the Sun, that additional glow is dramatically
reduced. That means you don’t get as much interference,
so you get much cleaner, photo-worthy images. The other reason these things get so sharp
close to totality is because the visible portion of the Sun becomes narrower. Normally, the sharpness of a shadow depends
on how far away you are from a light source: If you’re really close to it, the shadow
will be sharper, and if you’re farther away, it will be more fuzzy. But changing the size of the light source
can have the same effect. When you decrease the size of your light source
relative to the thing that’s casting a shadow, like, by covering up part of the Sun, the
shadows change. The ratio of things that are totally in shadow
versus only partly in shadow increases, and that gives those eclipse lights on the ground
sharper edges. So the next time you’re experiencing a solar
eclipse, take some time to look down. There’s a lot that those funny-looking lights
can teach you. And hey, if you’re not willing to wait until
the next eclipse, you’re not out of luck. At night, LED streetlights shining through tree leaves can project some pretty cool pinhole images, too. So ultimately, solar eclipses are cool in
a lot of ways, but in this case, they help highlight some of the amazing phenomena that surround us all the time! I hope you get the chance to check out these amazing shadows the next time you experience a solar eclipse, especially since looking
at shadows is a great way to see what’s happening without looking at the sun. Because, in case you’ve forgotten, that
is a really bad idea, and we have whole video that explains why which you can watch next. [♪ OUTRO]

Comments

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    New Message

    Ok those LED projections would have just convinced me I was in the matrix… glad I watched this before my town upgraded!

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    Master Therion

    In France, they don't get to see these crescent shaped astronomical events.
    They only get to see the croissant ones…

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    Christel Headington

    2 Eclipses I've seen I looked a reflections, in my rear view/side mirror and the other in the window of my neighbors pick-up. I did look on the ground, but didn't notice the tree shadows being strange.

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    Royce Valencia

    "Sore eclipses" or "Sorey clipses" right at the start of the video. What a weird mistake to leave in to the video, it's literally the first thing said.

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    Angl0sax0nknight

    You didn’t go into the weird effects that happen on the ground during an eclipse without trees. During the 17 eclipse I saw weird effects on the sidewalk. Possibly light bring refracted by the atmosphere.

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    Kevin Hoover

    But you didn’t really explain the mechanism involved – the why of it. You just said they do because they do.
    Why do they project on the ground, and why backwards?

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    Royer [RedKingRoy] Calixto

    I remember during the 2017 eclipse I looked down at the tree's shadows and saw those crescent shapes of light. I loved how they looked like.

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    D Gary Grady

    One thing you got backwards: the closer (or larger) the light source the softer it is and the fuzzier the shadows. It's related to geometric perspective. Edited to correct my own dumb mistake in the previous sentence. I originally wrote that smaller light sources produce softer shadows. Basically, the bigger the apparent size of the light source, the softer the shadows. The Sun is ginormous, but it's so far away (subtending only about half a degree in the sky) that it produces fairly sharp shadows.

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    Blake Nightshade

    I was wondering what those were. The August 2017 eclipse was the first day of the semester at my college. All the classes let out early to see the eclipse.

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    Surabhi Kumari

    I didn't even know that this phenomenon occurs during solar eclipse . Thanku SciShow for coming up with interesting stuff .

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    thisiszaphod

    We used a cullender to view the partial eclipse visible in the UK 20 March 2015, in the same way that is described here.
    Ingenious.

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    chegeny

    This jogged my memory that lunar shadows are so sharp and black on the moon because there is no refraction of an atmosphere. Astronauts avoided the shadows because they couldn't see anything in them, just complete darkness.

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    Pacca

    Ever since I noticed this phenomenon during an eclipse, I've noticed that the sun isn't the only thing that does it! Square lamps shining through trees make square shapes through the leaf shadows, it's super cool :3

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    Tristan Bellman-Greenwood

    To do this yourself, just make a really small hole with your hand. (like with your index finger curled up) This also help you see the progress of the eclipse without the special glasses.

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    Hoe YY

    There's one on Boxing Day this year. Singaporeans, this is a rare chance of being able to see an annular eclipse of the sun. Yes. The path of annularity passes over Singapore.

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    Dallas Meyers

    Two years ago I watched the total eclipse beneath a leafy tree with some of my young grandchildren. My favorite part of the experience was watching them dance around with excitement and delight because of the crescent shaped lights on their clothing and hands. It was truly a magical moment!

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    Pup314

    I saw something similar many years ago in New hampshire, where me and some riends went to see an annular eclipse. One in which the moon is further away from the Earth and doesn't entirely cover the sun but leave a ring of sun showing around it. I looked on the ground under a tree we were next to and Voila! Thousands of little sun rigs on the ground.

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    US

    The sad thing during the eclipse a while back are those elementary school kids making pinhole viewers, a lot of them got impatient, didnt have glasses, and they ooked directly at the sun. Would have been nice to see more videos on indirect viewing at that time as well.

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    Mike L

    While everyone was looking at the 2017 eclipse i was looking at the ground (We only had 1 pair of glasses). I made sure to get pictures

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    sststr

    Was there ever a final tally of just how many people went blind during the last solar eclipse? I read somewhere it was less than was anticipated, but they never put a number to it.

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    Herr Schmidt

    before the video I thought "d'oh it's because of the shape of the eclipse itself" but then i was pleasantly surprised about the little specific things you pointed out. Thx!

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    Jacob Martin

    I did see it! I was outside the path of totality in 2017 so the crescent refractions were the most interesting picture I could take.
    Thanks for clearing up the why!

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    TAmari

    I didn't even know this was a thing, that's super surreal to look at
    It's things like this that make me unsurprised that ancient people thought the sun was some kind of angry god lol

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    Jesus Ramirez Romo

    The 2017 eclipse wasn't visible in my area with the naked eye, but i could see the eclipse's shadow whn ligth entered trough a hole in a wall

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    GeneralShenanigans

    I wondered why when tried taking a photo of an 80 percent eclipsed sun i could see a green crescent half way down the photo from the sun.

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    rxg9er

    I saw the 2017 eclipse in Idaho. I saw waves of shadows moving along the ground for about ten seconds before totality started. I have not been able to figure out what they were. They weren't what was described in this video because I was in the middle of a parking lot, there was absolutely nothing obscuring the sunlight anywhere near me.
    edited for typos

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    Monica Alvarez Gonzalez

    MI HIJA TOMO FOTOS EN SU HABITACIÓN A LAS SOMBRAS EXTRAÑAS PRODUCIDAS EN EL MOMENTO DEL ECLIPSE, EN SANTIAGO DE CHILE, LA VERDAD QUE ES UNA FOTO EXTRAÑA PERO MUY LINDA YA QUE ESTÁ SOBRE UN MURO ROJO, SE VE IMPACTANTE Y BELLA, CARIÑOS

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    Tman64general

    Can you guys do a video on the phenomena known as "shadow bands?" I have questions and can't seem to find answers to them. What causes them and why are they only visible at the start and end of totality?

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    sirBrouwer

    for me it was the 1999 solar eclipse that i was lucky enough to see it. but i was a bit to young to actually notice it.

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    Tim Ebert

    You can get a great image of an incandescent filament by holding both hands over a torch at 90° and letting a minute crack of light through the cracks of your fingers on to a wall

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    SuperVstech

    One of the biggest things I noticed as the 2017 eclipse got close to totality was the temperature fo the day got SOOOOO much cooler.
    It was about 95F outside in western NC where I viewed the event.
    I was in a huge rest stop parking lot, and it was extremely hot. The sunlight was murder on our skin… as the moon blocked about 10% and more of the sun, it was like all objects around us came clearly in focus, and the light no longer was warm to the skin. Really a cool effect from the eclipse.

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    DianaDeLuna

    My sister was on fhe beach during the eclipse of 2017. Other people had brought fancy viewing glasses and pinhole boxes. My sister had only prepared for lunch rather than a celestial phenomenon, so she held out a cracker, which projected through the holes a dozen tiny crescents, all in formation on the sand.

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    Conor Norris

    since Pluto is tidally locked to its moon that mean on one part of Pluto the tree shadows would always look like this… if there was any trees

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    Loki Smith

    My dad was wearing a woven hat when we were watching the 2017 solar eclipse. As the moon covered more and more of the sun, we noticed that he had a bunch of crescent shaped lights all over his face😂. He then explained what pinhole cameras were and how the straw hat worked as one.

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    Dadson worldwide

    cant wait for the new up close orbital sat is in position around the sun. we will see the best resolution veiw of the sun we have ever seen.

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    Dadson worldwide

    I witnessed these and they do stand out. its such a eary feeling leading upto an eclipse.i can see why ancient ancestors got so worked up over them.

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    fartzinwind

    What about the wave like look across everything as the eclipse approaches. Not like vs dark Shadow, everything wiggling.

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    Sonja Johnson

    I had read that you COULDN'T photograph these circles! Interesting to know that it's actually possible. I wonder if tech has changed? The book I read this in was printed in the early 1990s…

    But hey! Brilliant! Now I know I can see even these formerly elusive features of an eclipse!!!

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    MakotoKamui

    I was at the National Weather Center for the 2017 eclipse, while there I saw a lot of the employees making pinhole effects by curling their thumb and forefinger into a tiny circle to project this same effect. Super neat trick!

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    woodfur00

    Ironically, I missed the crescent shadows in 2017 because it was too cloudy, but got a great view of the total eclipse itself. 10/10 would view again.

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    DemolitionDevon

    In the 2017 eclipse, we were just north of Seattle. Since we knew we wouldn't be able to look at the sun (too far north for totality), we spent the whole eclipse in our backyard. It was the perfect time of year and there were lots of leaves on the trees, so I got some AMAZING pictures! I didn't know about this phenomena until that day, so I have tons of pictures of my kids in weird shadows. Thanks for explaining this to us!

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