What Causes the Northern Lights (and where you should see them)


Thank you to Draper and its Hack the Moon
initiative for supporting PBS Digital Studios. Every winter thousands of tourists head North,
past the Wall and risking White Walkers, hoping to get rewarded with a glimpse of these amazing
multicolored lights. And while many succeed, many leave un-auroraed. Which begs the question: when, where, and
how is the best place to see an aurora? Auroras start with the sun. Specifically, when the Sun decides to shoot
billions of tons of charged particles mostly protons and electrons at the Earth, at speeds
that would do some serious damage… IF we were not surrounded by a protective
magnetic field. Our magnetic field redirects most of these
protons and electrons around us, but some of them follow Earth’s magnetic field lines
to their source: the magnetic poles. On their way to the poles, those charged particles
crash into atoms and molecules in our upper atmosphere, producing this. Because of how our magnetic field is shaped
and the height auroras typically happen above the Earth’s surface, the best place to see
an aurora is actually not right at the magnetic poles, but anywhere in an oval shaped zone
about 2,000 km from the poles. This zone is called the auroral oval and it’s
much easier to be in the auroral oval if you go North… because the southern one is mostly
over Antarctica and the Antarctic ocean. If you’re lucky, green. If you’re extra lucky, purple, pink, even
blue. If you’re the luckiest person on the planet,
red. But the most common aurora you’ll see is
green. The reason is kinda complicated, but welle
take it slow. First, you need to know a few things: one:
it’s the electrons from the Sun, not typically the protons, that make auroras. Two: as you go further up in our atmosphere,
there’s less and less of that atmosphere; and the gases that make it up change. Down here at sea level, air is 78% nitrogen,
21% oxygen, and 1% other stuff. In our upper atmosphere, about 80 kilometers
and up, there’s actually more oxygen than nitrogen. Three: at those high altitudes, UV light from
the Sun actually splits oxygen molecules into oxygen atoms. OK. So. When an electron crashes into an oxygen atom,
it excites it to what scientists imaginatively call… “an excited state.” Eventually, the oxygen will release its extra
energy as a photon of light. That photon can travel down to the surface
of the Earth, where you see it as part of an aurora. The exact color of that photon depends on
how much energy it has. Higher energy photons are greener, and lower
energy photons are redder. Now, here’s another fun fact about oxygen:
it has multiple different excited states, so it can absorb electrons of different energies. If it absorbs a high energy electron, then
a high energy photon is produced, aka green. If it absorbs a lower energy electron, then
a lower energy photon is produced: aka red. OK so at this point, you might be asking:
if oxygen is so cool that it can produce both green and red auroras, how come green ones
are much more common? If an oxygen atom absorbs a high energy electrons,
it relaxes back down and emits a photon one second later. But if it it absorbs a low energy electron,
it stays excited much longer — 110 seconds, to be exact. You can think of those time windows as aurora-killing
opportunities, because if a nearby molecule crashes into an excited oxygen atom, it totally
throws the oxygen off its game. The extra energy that would have gone to the
photon gets transferred instead to the molecule that crashed into the oxygen. And because red photons need 110 seconds to
brew, those red-photon-emitting oxygens are much more likely to get bashed before they
release photons than the green-photon-emitting oxygens. There are more wrinkles to this story — for
example, nitrogen can also make auroras — pinks, blues, reds, and purples… and hydrogen and
helium can too, but those are ever rarer. Now let’s talk about… You probably already knew this, but… at
night. Auroras are over a million times dimmer than
sunlight, so you’re not gonna see one during the day. Unless it’s the apocalypse. What that means, though, is that you’re
much less likely to see a Northern aurora in the summer, because the Sun is up so much
longer. So, at night, up North, in the winter. And try and avoid the Moon, if you can. And well, clouds. Also, the Sun is a mercurial beast. The number of particles and how fast they’re
going changes day to day based on different types of solar activity, but since it takes
a few days for the stuff to reach us, we can actually predict the best aurora-spotting
a few days beforehand. And yes, there’s apps for that. PBS is bringing you the universe with Summer
of Space which includes six incredible new science and history shows streaming on PBS
dot org and the PBS video app along with lots of spacey episodes from PBS Digital Studios
creators. Thank you to Draper and its Hack the Moon
initiative for supporting PBS Digital Studios. You know the story of the Astronauts who landed
on the Moon. Now, you can log onto wehackthemoon.com to
discover the story of the male and female engineers who guided them there and back safely. Hack the Moon chronicles the engineers and
technologies behind the Apollo missions. Brought to you by Draper, the site is full
of images, videos and stories about the people who hacked the moon. Are you heading out on an auroral journey? Make sure to bundle up aurorally, tell us
your auroral stories in the comments, and we’ll auroraraorarora next week. Try saying that ten times fast. Thanks for watching.

15 thoughts on “What Causes the Northern Lights (and where you should see them)”

  1. So, I work as an aurora guide in winter, and I will give you all a couple of pecees of advice:
    Do NOT use the aurora apps, if you are up north for just a few days you just have to stay outside and watch the sky as much as you can. So many times we have talked to people who missed good displays just because they where sitting inside looking at the app.

    Also, auroras can apear out of nowhere within minutes and be gone agian just as fast, just keep looking at the sky.

    And don't go to any major cities to see the aurora, the smaller the village is and the further away it is from major cities the better it is, light pollution is a killer for aurorawatching.

    Feel free to respond to this comment if you want to ask me any more questions about how to get to see the aurora.

  2. Aurora borealis at this time of day in this part of the country, localized entirely within your YouTube video

  3. I flew from LA to Rome, over the pole. I was treated to hours of auroras, first green, then red, then green again as we travelled south away from the pole. Hours and hours. Moving colors filled the sky. Everybody else watched the movie (Airplane?) I got one hell of a memory and a crick in my neck.

  4. I've always thought that the whole Aurora/Van Allen Belt system would make the most kickass Scifi energy shield idea- like instead of a random solid dome of sliver a la Star Trek you could have warships absorbing laser fire like nothing while spewing out a halo of multicoloured light. Wouldn't that look awesome in Star Wars?

  5. Apparently in spite of my casino losses I'm a very lucky person because I have seen all those different colors of Northern Lights in Northern Wisconsin

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