Archive for category Movies
These videos show some of the larger scale effects of flares on the Sun. In the video, you can see two big eruptions approximately 10 and 17 seconds into the video, from the active region in the lower left.
But look more closely – can you see a wave of coming out of each of these explosions? They are faint, and can be difficult to see, but they are there. These are examples of EIT waves, so called because they were first seen in the SOHO–EIT instrument. These waves are thought to be examples of magnetohydrodynamic waves that propagate in the corona. They are truly large waves; for comparison, the radius of the Earth is about 1/100th that of the Sun. By studying these waves we can learn more about the structure and properties of the solar corona. There is also some evidence that these waves have ‘knock-on’ effects on other parts of the Sun, perhaps causing other events at parts distant from the original explosion. Look at the video – what do you think?
We’re working on including data from NASA’s STEREO (Solar TErrestrial RElations Observatory, stereo.gsfc.nasa.gov) mission. It’s a mission consisting of two spacecraft, one drifting ahead of the Earth, and drifting behind, taking images of the Sun and the inner heliosphere. The concept behind the mission is to view the Sun as a three-dimensional object, from which we can better understand its surface structures and how it influences the inner heliosphere. This is the view from STEREO-A, and this is the view of the same event from STEREO-B. Both movies are of coronagraph data taken with the COR2 instrument; both STEREO spacecraft have the same instrument suites onboard.
We hope to have a stream of the very latest STEREO images very soon. Watch this space!
Cool loop arcade seen in SDO AIA 304.
What you’re looking at is a bunch of magnetic field lines, forming into loops of relatively cool plasma (50,000 K), at the limb of the Sun. For comparison, the surface of the Sun is around 4500-6000 K, and natural temperatures on the Earth’s surface are around 200 – 340 K.
There are quite a number of things going on here. Firstly, there are two active regions quite close by each other. Secondly, in the movie below (in AIA 171, which sees plasma at around 600,000 K):
Same loop system seen in SDO AIA 171.
you can see that some field lines appear to open up and a small faint eruption takes off. Finally, the loops form, with bright loop tops; it is likely that magnetic reconnection is taking place here. All in all, this is a very good example of just how complicated the activity on the Sun can be; with so much going on, there’s a lot to learn.
Helioviewer.org has been updated this morning to include some recent improvement to the movie generation process. The result of this update is that the quality of the movies that you see on Helioviewer.org has been greatly improved.
While Helioviewer.org has offered High-definition H.264 movies for several months now (encoded using the excellent x264 library), the amount of compression used was fairly high. The result of this was very small file sizes (around 1-5MB), but some noticeable compression artifacts; the effect of which was especially noticeable for larger movies.
For example, the below movie was generated on Helioviewer.org several days ago:
Example 1: In-browser movie before update (download video)
A number of changes were made to the H.264 encoding parameters in order to improve the quality, for example, whereas movies were previously generated using a constant variable bit-rate (-b 2048K), the newer movies use a different rate-control method called “Constant Ratefactor (CRF)” in order to achieve a desired level of quality.
Here is an example of a movie created for viewing in the browser using the new code:
Example 2: In-browser movie after update (download video)
What’s more, the “high-quality” download option is now much higher quality than ever before. Previously, when users clicked on the link below in the in-browser movie that says “Click here to download a high-quality version“, what they got was actually the same movie that was already playing in their browser, but packed in a container format compatible with the user’s operating system. With the update this morning, however, the high-quality download link now points to a separate and visibly higher-quality movie from what is shown in the browser. The high-quality option available now is actually a lossless movie, with respect to the underlying JPEG 2000 data archive used by Helioviewer.org.
Example 3: High quality movie after update (download video)
(Note: If you are having trouble viewing the above video, you can download an MP4 version directly from here.)
Of course, nothing comes for free, and that is true in the case of these improvements as well. The improvements made to quality come at the cost of increased movie filesize. For the standard-quality movie that is shown directly in the browser, the filesize has increased from by a factor of around 1.5-10x with the largest files around 50MB each. The real behemoths, however, are the high-quality (lossless) movies which range from around 50-300MB. It’s a lot, but try watching a few of high-quality AIA movies and you won’t ever want to go back again. 🙂
Update 2010/12/31: Thanks to Dark_Shikari on #x264 for some help making sense of some of the many rate control options available when encoding using x264.