Tuleva revontulikausi

Klikkaamalla saa parempi kartta.

Meille tulivat jo ensimmäiset kysymykset milloin voidaan katsoa taas revontulet. Vastaus riippuu leveysasteesta. Etelässä pimeys palautuu aikaisemmin kuin pohjoisessa.

Kuinka pimeää pitäisi olla? SGO:n tieteelliset kamerat toimivat kun aurinko on vähintään 10° horisontin alapuolella. Toki on mahdollista nähdä erittäin kirkkaat revontulet jo ennen sitä.

Yllä oleva kartta näyttää minä päivänä aurinko on kesän jälkeen ensimmäistä kerta 10° horisontin alapuolella Suomessa. Kannattaa muistaa, että kesäaikana yön pimein aikaa on klo 01 ympäri.

Meidän tieteelliset revontulikamerat eivät ole vältämättä näinä päivinä alkamassa mittauksinsa operatiivisista syistä.

Kartta ja teksti: Thomas Ulich, SGO.

Start of the Northern Lights Season

Click on map for better resolution.

Almost three weeks after the summer solstice, we start to get questions regarding when the Northern Lights can be seen again after the Polar Day. The answer depends on where you are: the further south you are, the earlier it will get dark enough.

How dark does it need to be? Our scientific cameras operate when the Sun is at least 10° below the horizon. However, if there are particularly bright Northern Lights, you might be able to see them already earlier.

The map above shows the days on which the Sun will be at least 10° below the horizon in Finland. Be aware, however, that due to summer time (daylight saving time), the darkest time of the night is around 01:00h in Finland.

Note further, that our scientific cameras will not necessarily be back on location on the first day that it is dark enough. Their annual maintenance might well delay the schedule.

Map and text: Thomas Ulich, SGO.

Northern Lights 31st January / 1st February 2017

[Helsingin Sanomissa 7.2.2017: "Revontulet sykkivät mystisesti" -artikkeli SGO:n ja Japanilaistutkijoiden välisestä tutkimusyhteistyöstä.]

Last week beautiful northern lights were seen across large parts of Northern Finland and Scandinavia. Already early in the evening after 19:00 EET (17:00 UTC), the lights appeared and by 21:00 EET the sky was filled with what we call "pulsating aurora". This form of aurora displays large patches of diffuse green light, which are flickering at various speeds, some flicker very fast. Pulsating aurora is very much a topic of active research, and our Japanese colleagues just launched the ARASE (ERG) satellite to study these specific lights from space. These efforts are combined with optical studies on the ground, and just in time for last week's northern lights, a special high-speed camera was installed at SGO, which can take up to 100 photos of the aurora per second!

From Sodankylä, four films of the aurora during the night of 31st January / 1st February have recently been published, two of which are from SGO:

The video above was made by taking all of the images of the regular all-sky camera of SGO, which are black-and-white images taken through filters for the auroral green, red, and blue lines, and combine these to create RGB (false) colour images. Images are taken every 20 seconds, and thus the video linked above is a time-lapse of the whole night, which is just 1min 30 sec long. (©2017 by SGO)

The video linked here is a result of a collaboration between SGO and Site-Eye Ltd., UK. Site-Eye have installed two long-term time-lapse cameras at SGO, one looking at the sky at a northerly direction, the other looking west across the river Kitinen. This video combines images from both cameras. (©2017 by SGO and Site-Eye Ltd)

The video above was taken by SGO's Thomas Ulich, who placed a camera looking almost straight up, with a slight tilt towards the south. This is the best direction to see what is called the auroral corona, a display, where the auroral rays all seem to originate from the same point in space. This is, however, just a result of perspective: the rays are in fact parallel. Images taken over 9 hours at a rate of four photos per minute were combined into a time-lapse film of about one minute duration. (©2017 by Thomas Ulich, see his blog post)

In the final video of this series, which was taken by SGO's Esa Turunen using a fish-eye lens to cover as much sky as possible, you can see the shapes of pulsating aurora especially well. They are patches drifting across the sky and flickering at the same time. The images were taken at a rate of approximately one per second. (©2017 by Esa Turunen)

Please note that in all videos linked here, the flickering of the aurora is aliased by the number of time per minute the images were taken as well as by the frames-per-second rate of the final time-lapse films.