Friday, February 16, 2007

NASA launch of THEMIS Satellite

Launch Date: Feb. 16, 2007
Launch Window Time: 6:05 p.m. - 6:23 p.m. EST
More info at the NASA website


The five NASA THEMIS satellites wil explore the dynamics of the magnetophere, the extended region around Earth of the Earth's magentic field. This should help to understand better when and how auroras are created. (Credits: NASA)


The THEMIS satellite's task is to measure details of the Earth's magnetic field, which is responsible for the phenomenon of the Aurora. If you've never seen it, have a look at this stunning time lapse movie, filmed in British Columbia, Canada.



While the basic physics of Auroras is more or less understood - electrons trapped in the magnetic field of our planet hit and ionise the gas of the upper atmosphere around the magnetic poles - these great phenomena still pose some riddles. For example, how come about all the different appearances of Auroras, and why can they change dramatically from gentle waves of light to wildly shifting streaks of colour?


An auroral display at the Peterberg Observatory at 49.6° northern latitude. Aurorae are quite rare at that distance from the poles, and you have to be very lucky - or have a good forecast - to see them. (Source: Sternwarte Peterberg)


Answers to these question are supposed to be found in a better understanding of the detailed dynamics of the magnetosphere. This dynamics will be explored by five satellites in an experiment called THEMIS, short for "Time History of Events and Macroscale Interactions during Substorms". Substorms here relates to strong, turbulent fluctuations in the Earth's magnetic field. Such substorms kick around the electrons, which then ionise oxygen or nitrogen in the atmosphere, which again, when recombining, emit the beautiful green and red lights.

If you think it's quite an idle project to work on improvements of Auroral Activity Forecasts, keep in mind that such predictions are extremely useful for those of us living at comfortable distance from the poles not to sleep on the rare occasions when we can witness these fantastic lights at low latitudes.

Further reading:




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16 comments:

QUASAR9 said...

Hi Stefan, great post, great video
Auroral mechanism & Aurora colours
A forbidden mechanism or forbidden line is a commonly misunderstood concept in chemistry. It is a spectral line emitted by atoms undergoing energy transitions not normally allowed by the selection rules of quantum mechanics. In chemistry, forbidden means absolutely impossible due to natural laws but with the assumption of an ideal symmetry.
Forbidden emission lines have only been observed in extremely low-density gases and plasmas, either in outer space or in the extreme upper atmosphere of the Earth. Even the hardest laboratory vacuum on Earth is still too dense for forbidden line emission to occur before atoms are collisionally de-excited. However, in space environments, densities may be only a few atoms per cubic centimetre, making atomic collisions unlikely. Under such conditions, forbidden line transitions may account for a significant percentage of the photons emitted.
Forbidden line transitions are noted by placing square brackets around the atomic or molecular species in question, e.g. [O III] or [S II]. Forbidden lines of nitrogen ([N II] at 654.8 and 658.4 nm), sulfur ([S II] at 671.6 and 673.1 nm), and oxygen ([O II] at 372.7 nm, and [O III] at 495.9 and 500.7 nm) are commonly observed in astrophysical plasmas. These lines are extremely important to the energy balance of such things as planetary nebulae and H II regions.

stefan said...

Hmm,


on NASA's THEMIS Mission Launch Blog one could just follow how launch was postponed once more for 24 hours within the last minutes of the countdown because of "upper-level winds"...

You need to be patient if you want to go to the stars ;-)

Rae Ann said...

Beautiful! I've never seen them in person. The time I was in Alaska in Dec. 2000 must have been a solar quiet time or something. And it's a good thing to monitor that electromagnetic activity because it can have big effects on communications satellites and electrical stuff on earth.

amaragraps said...

Here is a view of auroras from Antarctica by Denis Barkats and colleagues that you might like (posted by Clifford during his cosmicvariance stint). The comments are relevant to this discussion too.

amaragraps said...

Here is a photo you might like of Comet McNaught and an aurora dancing with each other...

stefan said...

As an update, according to the launch blog, launch was finally successful on Feb. 17, 2007, and all five satellites have separated and are on their way to their respctive orbits.

stefan said...

Dear Rae-Ann,


I do not know where you live, but the frequency of auorae depends strongly on how far you are away from the geomagnetic poles, and from the current phase of the 11-year solar activity cycle. Here is a table on the frequency of aurorae in Britain, and you see a strong decrease from Lerwick/Shetland (60° North) to Southhampton/South Coast (50° North) from 160 to 10 (40 to 0) aurora nights per year at solar maximum (minimum).

So, for me at Frankfurt, for example, that means that I could expect several aurora nights per year around solar maximum! That's not so little, but not all aurorae are big and bright, and of course not all nights are clear.

There must have been a quite impressive aurora last December which was visible far south, but I missed it. It was even more unuasal since we are right now close to a minimum of solar activity.

I have seen an aurora here in Germany only once, in November 1989. Sky was all red, and a little bit green toward the northern horizon. The reddish glow was similar to the view of a cloud cover lit by city lights, but you could see many stars through this red curtain, so it weren't definitly no clouds.

Lines of euqal average auroral frequency are called auroral isochasms - maybe I will try to find a map somewhere...

stefan said...

Dear Amara,

thank you for the link to the Denis Barkats post and the great photo of McNaught and an Aurora.

Do you know where this last picture has been taken? I have a stupid question, these blob-like clouds in the sky, are these the Magellan clouds? I do not very well the Southern skies...

stefan said...

Hi Quasar,

thanks for the comment on forbidden lines - although I have to say, I find it a bit confusing, making things sound more mysterious than they are.

Technically speaking, if an excited atom emits light, there is a whole expansion of terms that describe coupling of the atom to different modes of the electromagnetic field: electric dipole, magentic dipole, electric quadrupole, magnetic quadrupole, and so on. Each of these terms comes with its own selection rules, and a the transition amplitudes strongly decrease from term to term.

Now, normally not allowed by the selection rules of quantum mechanics relates to the first term, the electric dipole. But if the selection rules do not allow an electric dipole transition, other transitions (with other selection rules) will be allowed in general. The thing is, the transition amplitudes are then much lower, and the atom would stay in the excited state much longer than when de-excited by a electric dipole transition. Now, if your atoms are in a dense enough environment, de-excitation will happen by collsions before higher electromagnetic transitions will take care of it. That's why one does not see spectral lines of these transitions for dense gases.

For some historical reason, these transitions are called forbidden, but keep in mind that they are forbidden just for the lowest term in a series expansion, and they occur as soon as conditions of density etc. allow the higher terms to play a role...

amaragraps said...

That photo came from a spaceweather comet McNaught page. It was taken in Queenstown, New Zealand. The same photographer took this APOD photo. Following that was a discussion on the 'blobs' in the photo on an APOD discussion forum (found the other day by acccident), where that particular photo is discussed. The one in full view is the Small Magellanic Cloud and the one in the upper edge is the Large Magellanic Cloud. In the photo I linked to here, the Large Magellanic Cloud is the "upper blob". Looks nice, for us northern observers, doesn't it? I've never seen the Magellanic Clouds with my own eyes.

stefan said...

Dear Amara,

thank you for the links and the explanation! I have seen the Magellanic Clouds once, on a beautiful trip to Namibia :-). The sky there was just great!

Best, stefan

amaragraps said...

Dear Stefan,

The only people I know who have travelled to Namibia were working on the H.E.S.S. project. Are you, by coincidence, involved with that project? Just curious....

Bee said...

Dear Amara,

how was your trip? No, Stefan isn't involved in the HESS experiment. It was me who dragged him to Namibia (and SouthAfrika (and Botswana)). But the night sky in Namibia is just the best - which is kind of surprising considering the sand and dust that covers the whole country. Best,

B.

amaragraps said...

bee-My trips were Interesting and wonderful with a heavy dose of surreal.

Interesting- At ESTEC in Noorwijk, I spent a day with other data reviewers of the PDS products from the Rosetta mission. I like being a data reviewer, and I like shaping something into a form with which the whole community (in this case, the dust community) can use.

Wonderful- At Nice, I worked with my colleague on a paper and I explored the city as a possible new location for my life. Of the city I have mixed thoughts still, but maybe I can find the rough edges attached to the polished glint to make it more appealing to my character. And the daily life _works_. The astronomers spend almost no time on bureaucracy and broken infrastructure stuff, no queues to pay bills, mail delivery is regular and fast, utility companies do their jobs properly, and on an on. I could gain back my hours I lose every week on those stupid things. And the more time I spent at the Nice Observatory, the more I fell in love with the place and the people. The people there do world class science; also funny, hardworking, friendly and fully supportive of my work.

Surreal- On the Alitalia flight between Rome and Amsterdam, my small blue purse of keys inside of my luggage went missing. Inside were also a handful of memory sticks (labelled with my mobile phone number) and my work badge. In my sleep-deprived state, I didn't discover the missing purse until I returned to Rome, entering my house and car with spares. Upon checking all possible locations for the keys (from a distance), I began the appropriate steps to remedy the situation, but I needed to leave 12 hours later for my second trip. Upon arriving in Nice, my mobile quit, 'zapped by the airport xray machines' (the repair shop said). Nervous about not having a way for anyone finding my keys to contact me, I bought a new phone as soon as possible, three days after the zapping incident. Sure enough, there was a call waiting for me, but it was a wrong number.

After my wonderful week in Nice, I returned to Rome, again, and tried to use my precious remaining key to enter my home but the location in my luggage of the outer pocket where I had put the key to be easily findable by me, was not the best location because the conditions of transport had bent my house key about 20 degrees and it wouldn't fit into my front door lock. Luckily my next door neighbors had a hammer (and a good sense of humor), and they pounded my key back into shape so that it could fit into my front door. The next morning, after unpacking and trying to put my life back in order, I went to leave for a doctor's appointment (to try to learn a reason for my fainting spell one month ago), and my car's battery was dead. An hour later, I had a new car battery, but my appointment that I had waited for one month was past. Upon arriving at my job, I learned that it is not enough to tell my workplace that my badge was lost/stolen, I must also 'denounce' it via a written report from the Carabinieri, the Italian military police, before I can have a new badge made for me. And the one key that I did not have a copy of was my office key.

The next morning, I 'denounced' my lost purse, in particular, my lost badge, which as far as I know, serves the only purpose of allowing me through the gate of my workplace and it records my hours at work. It was my first visit to a Carabinieri in Italy and they didn't seem to be particularly busy. I was their only 'customer', during the time that I was there with the phone ringing one time. They seemed intrigued by my birthplace (Honolulu) on my Italian identity card. The man who filled out the report had some trouble with the Microsoft program because it quit and he needed to enter everything a second time, and the toner cartridge for his laser printer was leaking black ink that made big smudges on my official report. But I have my denuciation report in hand, and as soon as the one person who is responsible for issuing badges returns from vacation, I will be able to have a new badge. Then maybe my alternate surreal universe will cross with the one that everyone else lives in and I can have a bit of normality again.

Aren't you glad you asked ? ;-)

Plato said...

This is a good post Stefan.

I like to keep advance of what is happening with the sun/earth relation, so I use a script written here that let's me know in advance if there will be activity with regards to the aurora.

AS well, the Soho link of the sun and helioseismology help us in this regard. Amara knows what I mean here.

Bee said...

Dear Amara,

Aren't you glad you asked ? ;-)

Yes, indeed, I am :-) I would have missed a too interesting story! I am sorry to hear about your trouble though, and I hope everything worked out fine. I have been in Nice repeatedly, except for it being pretty touristic, its just a beautiful city. I especially like the small narrow streets, and the colors. All the best,

B.