Starship Asterisk*

Hello Everyone!

I'm excited to join the asternauts here to share some videos produced by the XRT team. XRT (X-Ray Telescope) is one of three instruments aboard the Japanese satellite Solar-B, or Hinode (sunrise). Hinode launched in September of 2006 and has been sending back wonderful new and scientifically valuable images ever since.

XRT has long had a "Picture of the Week" website, where images and movies get posted on a [oft-semi] weekly basis, but we've now also introduced a YouTube channel to hopefully reach more people and support things like embedding our videos in message boards.

I'll be posting to this thread each time a new video gets uploaded to YouTube, which will include brand new videos as well as new-to-YouTube versions from the "Picture of the Week" site. This should be something like twice a week until most of the old videos have YouTube counterparts, and then weekly after that. (Some of you may have already seen our eclipse video, which was linked in last week's APOD about the event.)

Now I'll stop chattering and leave you with this great video of the solar cycle ramping up over the last three years. What we see here is the upper atmosphere, or corona, of the sun, which contains plasma at much higher temperatures than the solar surface (photosphere) and thus emits at higher-energy wavelengths and is clearly visible in x-rays. The structure of the corona is largely determined by the emergence of magnetic fields resulting from the solar dynamo, which drives the solar cycle and is still somewhat poorly understood.
We'd love to hear from you, so please feel free to leave comments/questions here or on YouTube. You can also email me at xrtpow "at" gmail "dot" com.

Today's movie attempts to follow a fixed location on the sun as it comes back around after each rotation period. Each frame advances time by one Carrington rotation period, around 27.3 days. Following one spot on the sun is a tricky endeavor because the sun is not a solid body and is therefore subject to differential rotation, meaning that different latitudes have different rotation rates. The polar regions of the sun rotate fully about once every 34 days, while material at the equator takes only about 25 days. Richard Carrington used low latitude sunspots to determine the rotation period of the sun and came up with a sidereal period of 25.38 days, which, because the Earth is orbiting the Sun, appears to us as 27.28 days. In this movie, several active regions can be observed to appear, linger for a rotation or two, and then dissipate. But this perspective is perhaps even more interesting for illuminating the dynamic nature of coronal holes, the dark regions of cooler and lower-density plasma, which can be seen here morphing and migrating throughout the corona.
And here is the image posted to our XRT "Picture of the Week" page, which pulls out some of the remarkable evolution of coronal holes shown by the movie:

WOW! The first video is Great! It's like the sun is winding itself up to do something. (I hope it doesn't head in our direction!)
It would be a good video to fill in for APOD on the weekend.

A new-to-YouTube movie for your enjoyment. Tune in Friday for any XRT data capturing the effects of Comet Lovejoy; we're not sure, but hopefully we see something... *fingers crossed*

On 2011/10/31, XRT observed an unusual series of jets from NOAA active region 11330. One of the early results from Hinode/XRT was a newly apparent preponderance of x-ray jets near the poles, and jets have been the focus of several previous "Picture of the Week" installments. These features are thought to be streams of plasma escaping the sun along open magnetic field lines after an interaction between the open line and a small loop nearer the surface, though the physics is not fully understood. What makes this event unusual is that the jets persist for so long in one location. The attached movie shows jets in one spot for around four hours between 13:40 and 17:50 UT.

It took me a week or so to recover from the disappointment of not seeing any trace of Comet Lovejoy in XRT data, but now we're back with another installment:

Today's movie shows NOAA Active Region 11374 as it develops over about a day and a half from Dec 11-13. In the left panel we have images taken through XRT's thin beryllium filter, which is sensitive to coronal material with temperature in the neighborhood of 8 million Kelvin. The 304-Angstrom passband of AIA, sensitive to chromospheric material at around 50 thousand Kelvin, is shown in the right panel. (For reference, the surface of the Sun, or photosphere, is at a temperature of around 5800 K.) Because temperature increases with distance above the photosphere, here were are afforded a nearly simultaneous view of two different layers in the solar atmosphere, with the XRT images sampling material that sits around 10,000 km above the material shown by the AIA/304 channel.

Hurray Asternauts, XRT did indeed see Comet Lovejoy! The detection was *extremely* faint, and if you follow this link to our original post, you'll be able to see why I had a hard time realizing that we'd seen it all. I'm sure you're all up on Lovejoy's story, so I'll skip that and just mention that this is a "base difference" movie. Each frame has been subtracted by some "base", which in this case is an average of many frames that did not contain emission from the comet. In case anyone is wondering, we did make observations for the inbound flight as well but with less luck. Some additional image processing may lead to a sure inbound detection though, so stay tuned for that. These are likely higher energy photons than any of the other videos you may have seen, so we're excited to have seen anything at all!
And a note for the aficionados: This is XRT's thinnest filter, Al Mesh, which has some sensitivity from soft x-rays to the EUV. This includes a small component at 171 Angstroms, which is the passband that AIA saw the comet so beautifully, so it's possible that XRT is seeing essentially the same thing as AIA. It would perhaps be a bit more interesting if we're seeing higher energy, and not the same, photons as AIA/171, but that analysis is still forthcoming.

Here are 4 videos just uploaded to YouTube. Enjoy! Head over to the actual YouTube pages for descriptions.

Today we have a set of three videos all showing different aspects of solar flares and coronal mass ejections. The first shows a particularly "flare productive" active region as it evolves over 4 days. In the left panel, a thinner filter combination is overexposed to show extended structure, while the right panel uses a thicker filter combination to observed the bright flare kernel.
In the second video, we have an eruption that occurred on the west limb (the confusing convention in solar physics is opposite that of traditional maps). A linear structure develops during the eruption, just before the main brightening, and is possibly a current sheet or "x-point" where magnetic reconnection is taking place.
The last video shows a coronal mass ejection (CME) that accompanied a solar flare (as is usually, but not always, the case for the larger flares). Though there is much still to be learned, magnetic reconnection is the prime suspect for the driver of both flares and CMEs.