Archive for March, 2011

User highlights: a cool loop arcade.

The event below was found and shared by and YouTube user “LudzikLegoTechnics” – thanks for that! It’s a wonderful example of a cool loop arcade forming and evolving.

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.

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Temporary AIA/HMI availability outage, March 8-9 2011

Some of you may have noticed that we have not had any new AIA or HMI images in the past few hours. AIA and HMI are still taking data, and that data is still being beamed down to the Earth, where it is being stored and distributed around the world. The problem lies in the pipeline we use to convert that AIA and HMI science data into images that are used by the Helioviewer Project. The Helioviewer Project team is currently working to find and fix the problem. Images from other instruments, such as EIT and LASCO C2 are unaffected.

We’ll post a blog entry as soon as AIA and HMI images become available again, and images that are currently missing will be filled in.

Sorry for the interruption, but we’ll be back with the latest solar images for you to explore, as soon as we can.

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Fast eruption in AIA 171

After many large and interesting events yesterday, the Sun produced this spectacular eruptive event late yesterday.

Fast eruption in SDO AIA 171.

This lead to a coronal mass ejection with a speed of around 2200 km/s, one of the fastest we’ve seen in the current solar cycle. Interestingly, this erupted material had a lot of bright emission in the AIA 171 pass band, indicating bright or dense (or both) material at around 1,000,000 K, which whilst not unusual, isn’t too common either. The bright loops remaining at the surface of the Sun are known as post-flare loops.

A high quality version of the above movie can be obtained here.

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Moon nibbles Sun: a partial eclipse of the Sun by the Moon as seen by SDO.

Today the Moon is passing across the field of view of AIA on board SDO. AIA sees this as a partial obscuration of the disk of the Sun. If you look at an AIA image near 15:00 UTC (March 04, 2011) you can clearly see that a big round object – our Moon – is blocking a portion of the solar disk, and some off disk-emission.

A partial eclipse of the Sun by the Moon as seen by SDO

Moon nibbles Sun: a partial eclipse of the Sun by the Moon as seen by SDO

If you zoom in to the image, you can see that the edge is not perfectly circular. Those are mountains and valleys on the Moon seen in silhouette.

This partial eclipse of the Sun as seen by SDO was expected, since we know the orbits of SDO, AIA, the Sun and the Moon. You can find out more about the eclipses SDO will see (and has seen) by checking out the SDO operations calendar.

As well as being stunning displays of orbital mechanics, partial eclipses of the Sun by the Moon are also very useful in helping us understand the data we are taking with AIA. If you look closely at where the disk of the Moon meets the Sun, you can see a little bit of color is in the dark disk of the Moon. Since we know that the Moon does not emit radiation (and it is not transparent!), the light causing that little bit of color must have come from the Sun. The only way that light could appear to have come from the Moon is due to slight imperfections in the telescope. By measuring how much light leaks from the bits of the image where the Sun is, over to the bits of the image where the Moon is, we can characterize the imperfections in the telescope. And once we have done that, we can use that to improve the images by enhancing the image to take out the effects of the telescope imperfections.

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