Bell Tone
Hi, this is Alex Young. I'm a heliophysicist
at NASA's Goddard Space Flight Center. And many of you may have seen the
video recently that showed the sun for the past three years
observed by the Solar Dynamics Observatory. I also saw this recently,
thought it was a really cool video and I want to share with you some of the interesting
features I noticed in the video. -MUSIC-
If you see that big black disk that moves over the sun, that's
the moon--what we call a lunar transit. That's when the moon is moving
between the sun and the SDO spacecraft.
It almost looks like a perfect circle, but if you look really
really close on the edge, you see these little tiny humps. Those
are the mountains on the moon. Just an amazing thing you can see with
these incredibly high-resolution cameras. We're looking
at the 171 angstrom wavelength. This is extreme
ultraviolet. And it's showing us the solar atmosphere at about
a million degrees Fahrenheit. And if you look at this image, you can
see all of these bright patches, these are active
regions associated with sunspots. And then you even see
loops. These are huge structures many times the size of
Earth that are magnetic fields holding in
this hot solar plasma. One of the
things that's amazing about this is there's so much stuff going on in this
image as we're looking over time. There's a really big
flash on one side of the sun--that's a solar flare. And in this
case it's the largest solar flare that happened during this particular
solar activity cycle. One of the coolest things that we
can see from this video is the simple fact that the sun
rotates around its axis. The center near the equator
takes about 25 days for it to rotate all the way
around and come back to the same place. Now, I'm pointing this out because
the sun has a special feature, something called differential rotation.
A point on the equator actually moves faster
than a point closer to the north or south pole.
One thing that happens is sometimes the images move, the sun
moves around or even rolls. But that's actually the
spacecraft moving, not the sun. SDO has to
occasionally roll the entire spacecraft in order to
calibrate the cameras and instrumentation on board.
If you notice, those bright patches, those active
regions, start off towards the poles
of the sun and as we move in time, they start to
slowly creep towards the equator. This is part of what we call
the solar activity cycle or solar cycle. As we
move from very low activity, with very few sunspots,
to high activity, with a lot of sunspots.
This is something that happens again and again, and it's happened
for millions of years. -MUSIC-
-MUSIC-
And now we can see the sun
in multiple wavelengths of light simultaneously. We see
the visible sun, where you can see the dark sunspots.
And then if you look at the 171 extreme ultraviolet
you see the corresponding bright areas and the magnetic
loops coming from them. If we go to the 193
you see even more structure and you see these dark patches.
And this is where magnetic fields are open out into space
letting out something called the solar wind in these very
fast streams of particles. And then the last one, the red
one, is 304 angstrom, and this is showing us what we
call the chromosphere. And these red areas are often visible
when you see the sun from total solar eclipse.
-MUSIC-
Did you see that little tiny black
dot that's close to the north pole on the sun? That's Venus.
Every hundred years or so, it moves in front of the sun
giving us this rare and amazing astronomical
event. -MUSIC-
-MUSIC-
Beeping