As of yesterday, this picture of mine has over 20,000 views on Flickr.
Wednesday, February 29, 2012
Leap Day
Due to events astronomical, today is Leap Day. Why?
A year is how long it takes the Earth to go around the Sun and back to where it started, and a day is how long it takes the Earth to spin about on its axis. Everyone knows there's 365 days in a year, but that's not quite right. It's more like 365 days and 6 hours, or 365.25 days. Multiply that by two and you find 730.5 days in two years. 1095.75 days in 3 years. 1461 days in 4 years. But wait! There are no quarter-days in the calendar, so the calendar hasn't been keeping track of those! It says there are only 1460 days in 4 years. After 4 years, our calendar is one day behind! What can we do about this? It just doesn't work out!
Well, every four years we'll just throw another day in there somewhere. Hence Leap Years. The problem is the amount of time it takes Earth to go around the Sun, the period of Earth's orbit, isn't an integral multiple of the period of Earth's rotation, which just means if you divide the period of orbit by the period of rotation, you don't get a whole number. Clearly there was no quality control when the solar system was made, because this is totally unreasonable.
If the solar system is a clock, it's as if the teeth on one of the gears aren't spaced evenly, so every once in a while someone has to reset it. But what can you do? We'd have to move the Earth or change the speed of its rotation to 'fix' the clock.
It's actually worse than that because a year isn't really 365 days and 6 hours long, more like 365 days, 5 hours, 49 minutes long. Now we're counting an extra 44 minutes every time we do a Leap Day, so to make up for that we have to skip Leap Day on years ending with 00 (like the year 1900), unless they're divisible by 400 (like the year 2000). Madness...
A sunset, because I don't have any relevant pictures. Sunsets happen on Leap Days.
A year is how long it takes the Earth to go around the Sun and back to where it started, and a day is how long it takes the Earth to spin about on its axis. Everyone knows there's 365 days in a year, but that's not quite right. It's more like 365 days and 6 hours, or 365.25 days. Multiply that by two and you find 730.5 days in two years. 1095.75 days in 3 years. 1461 days in 4 years. But wait! There are no quarter-days in the calendar, so the calendar hasn't been keeping track of those! It says there are only 1460 days in 4 years. After 4 years, our calendar is one day behind! What can we do about this? It just doesn't work out!
Well, every four years we'll just throw another day in there somewhere. Hence Leap Years. The problem is the amount of time it takes Earth to go around the Sun, the period of Earth's orbit, isn't an integral multiple of the period of Earth's rotation, which just means if you divide the period of orbit by the period of rotation, you don't get a whole number. Clearly there was no quality control when the solar system was made, because this is totally unreasonable.
If the solar system is a clock, it's as if the teeth on one of the gears aren't spaced evenly, so every once in a while someone has to reset it. But what can you do? We'd have to move the Earth or change the speed of its rotation to 'fix' the clock.
It's actually worse than that because a year isn't really 365 days and 6 hours long, more like 365 days, 5 hours, 49 minutes long. Now we're counting an extra 44 minutes every time we do a Leap Day, so to make up for that we have to skip Leap Day on years ending with 00 (like the year 1900), unless they're divisible by 400 (like the year 2000). Madness...
A sunset, because I don't have any relevant pictures. Sunsets happen on Leap Days.
Saturday, February 25, 2012
In which there is a rocket.
One of the ways researchers study auroras is by launching sounding rockets which carry instruments to measure things like electric and magnetic fields, currents, or particle density or energy. This provides a direct measurement of the actual conditions in the aurora, rather than just inferring the conditions using data from cameras on the ground or satellites at much higher altitudes. Sunday I returned to Fairbanks from participating in just such a launch. If you want to know more about the rocket, you should read Ian's post. Ian is a grad student at the University of New Hampshire who spent the previous ~1.5 weeks with me in the Arctic circle waiting for this rocket to fly over. Which is really the thing I'm getting at here: I spent the last ~1.5 weeks in the Arctic circle, manning equipment and watching auroras.
We stayed at a cold war era early warning radar site about a mile outside the town of Fort Yukon, a few miles inside the Arctic circle. Crossing 8 miles over the Arctic circle is kind of a non-event - It's like crossing the border into Canada: Okay, you take a picture of the sign, and get excited and stuff, but it's all just pretend, nothing really changes about the scenery. Though the Arctic circle is more of a 'real' boundary than a state or country border, it's not like you're instantly on the windswept tundra hiding from polar bears. But anyways...
We (Ian and I) arrived in Fort Yukon via small plane (did I mention it's not connected to the road system?) on the morning of Friday the 10th. We got our bags and met up with our ride to the station. A brief tour of town on the way, and then it was down to business: Unpacking and installing 13 cases and 3 wooden crates (!) of camera gear. Got most of it together Friday night and Saturday morning, with some final touches after first use. A third researcher, Hans, showed up Saturday to complete our crew. We then sat around with no visibility under cloudy skies until Tuesday the 14th, when we had clear skies and a fantastic aurora show. We decided not to launch that night because the aurora wasn't exactly the kind we were looking for, and we still had some equipment problems to wring out, so we went outside to watch. It was Ian's first aurora, and it was a damn good one.
I shot video too: Have some Valentine's Day auroras:
After that, we had several more nights of clouds and/or low activity. The daily routine was to start up computers and cameras at 7pm for a launch window that opened at 8pm, then surf the internet / read a book / play a game until the window closed at 2am. Then sleep until lunch, do whatever maintenance needs done, and start again. On Saturday the 18th I commented that 'tonight is the night', as the sky was clear and the indicators looked good, and I was right. Another very nice aurora:
And this time we launched the rocket! Liftoff at 05:41UT, or 08:41pm local time. The rocket reached 325km altitude, and the whole event was over in 10 minutes. I didn't even get to see it because I was inside pointing the science cameras. But I had my own cameras running again, so here's the aurora we launched into. My favorite is the blob of red aurora that appears above the building:
A Japanese group has some all-sky cameras running at Poker, and they got a shot of liftoff:
Credit for that shot to Ryuho Kataoka.
Here's a few more photos of the rocket as it flew up, but they're in full resolution, so I'll link rather than embed:
From Mark Conde
From Craig Heinselman
Here's a mapped projection of the Fort Yukon all sky camera. The time at the top is universal time: The rocket launch was at 05:41 and the flight took around 10 minutes. The dotted line shows the rough trajectory of the rocket. You can click the play button at the bottom.
Tuesday, February 21, 2012
Pulsating Aurora
There were auroras again Sunday night, but after launching the rocket Saturday and spending Saturday night and Sunday packing equipment and flying back to Fairbanks, and then a big celebratory dinner for everyone involved with the launch, I was more interested in sleeping than watching the aurora. I woke up at 3am and looked outside, and the aurora was still going. Okay, if you insist. I set my camera just outside the front door and went back to bed. Here is the video:
For the first few seconds (about 20 minutes of real time) you see the arc that was just south of me, but then things change. The arc seems to expand and fade, and what's left are a bunch of patches that flicker in brightness while seeming to drift past like clouds. This is a pulsating aurora.
Pulsating auroras are pretty common, yet few people see them. One reason is they typically occur in the early morning hours when most people are asleep. Another is they're dim (I shot this at f/4, 8 seconds and ISO3200!) so your eyes need to be pretty dark adjusted. The patches brighten and dim on the order of seconds to up to a minute or so, but typically around 10-20 seconds. Of course, every second of this video shows 5 minutes of real time, so you see them flicker several times per second because of how fast the video is.*
The Earth's magnetic field lines convect over the pole towards the night side, then back towards the day side through the auroral oval. So here in Fairbanks, right under the oval, we have field lines drifting towards the Sun, which means east-to-west before midnight and west-to-east after midnight. I can't find an animation or diagram of this online, so here's a 60-second MSPaint drawing I just did:
This is looking down at the Earth from above the north pole, and the Sun is towards the top of the screen. The green circle represents the auroral oval, and the black arrowed lines show the path of the magnetic field lines as they convect down across the polar cap (the area inside the oval) and then back towards the Sun through the oval. The Earth rotates couterclockwise when viewed from here, so the red dot represents the location of Fairbanks before midnight (on the left) and after midnight (on the right).
So one thing to notice in the video is that the pulsating patches are drifting west-to-east, because this was taken after midnight (video is facing south). This produces what I think is a pleasing effect as the stars drift through the shot in the opposite direction as the auroral patches. But here's something even more interesting: The patches are tied to processes occurring in the magnetic field, so as you watch the patches drift across the sky, you're actually watching the magnetic field lines convect past. The field lines are invisible (or nonexistent, or whatever), but when you watch those patches drift through, the field lines are sticking down through those patches, and so moving past at the same speed as the patches.
Or so we think. This is still an area of active research :)
________________________________________________________________
*not to be confused with flickering aurora, which brightens and dims many times per second in real time. This cannot be filmed without very expensive equipment. Think on the order of $50,000.
For the first few seconds (about 20 minutes of real time) you see the arc that was just south of me, but then things change. The arc seems to expand and fade, and what's left are a bunch of patches that flicker in brightness while seeming to drift past like clouds. This is a pulsating aurora.
Pulsating auroras are pretty common, yet few people see them. One reason is they typically occur in the early morning hours when most people are asleep. Another is they're dim (I shot this at f/4, 8 seconds and ISO3200!) so your eyes need to be pretty dark adjusted. The patches brighten and dim on the order of seconds to up to a minute or so, but typically around 10-20 seconds. Of course, every second of this video shows 5 minutes of real time, so you see them flicker several times per second because of how fast the video is.*
The Earth's magnetic field lines convect over the pole towards the night side, then back towards the day side through the auroral oval. So here in Fairbanks, right under the oval, we have field lines drifting towards the Sun, which means east-to-west before midnight and west-to-east after midnight. I can't find an animation or diagram of this online, so here's a 60-second MSPaint drawing I just did:
This is looking down at the Earth from above the north pole, and the Sun is towards the top of the screen. The green circle represents the auroral oval, and the black arrowed lines show the path of the magnetic field lines as they convect down across the polar cap (the area inside the oval) and then back towards the Sun through the oval. The Earth rotates couterclockwise when viewed from here, so the red dot represents the location of Fairbanks before midnight (on the left) and after midnight (on the right).
So one thing to notice in the video is that the pulsating patches are drifting west-to-east, because this was taken after midnight (video is facing south). This produces what I think is a pleasing effect as the stars drift through the shot in the opposite direction as the auroral patches. But here's something even more interesting: The patches are tied to processes occurring in the magnetic field, so as you watch the patches drift across the sky, you're actually watching the magnetic field lines convect past. The field lines are invisible (or nonexistent, or whatever), but when you watch those patches drift through, the field lines are sticking down through those patches, and so moving past at the same speed as the patches.
Or so we think. This is still an area of active research :)
________________________________________________________________
*not to be confused with flickering aurora, which brightens and dims many times per second in real time. This cannot be filmed without very expensive equipment. Think on the order of $50,000.
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