Tuesday, 24 March 2015

Solar Eclipse – Racing the Moon!

It's the morning of the eclipse on 20th March, 2015. It looks hopelessly cloudy in Sodankylä. Do I have to abandon the live webcast? Suddenly, my 7-year old daughter shouts that there're some blue patches between the clouds. Will the weather improve? Together, we have a look at two different weather predictions on-line: they disagree with one another. Time to call the on-duty meteorologist, who tells that there's a snow storm coming in and that the best chances to watch the eclipse will be to go to the western border of Finland.

Time to pack up and drive towards Kittilä, stopping only briefly to drop my daughter off at her school. I call my colleague, who lives in Kittilä, and he tells it's snowing properly over there. I can only hope that it passes by the time I get there. Half there, in the area of the village of Tepsa, the snow storm hits. Almost a white out, visibility is low. Am I going to see anything at all? The phone rings. A journalist from Helsingin sanomat, who wants to know about our live webcast. Yes, we will do it, I tell him, if I can only find clear skies. He's somewhere south of me, heading to Kittilä, too, and has clear skies. He doesn't know about the snow storm yet.

In Kittilä it's snowing lightly. Stopping on a supermarket car park, I have a look at the weather radar data on-line. It shows snow showers moving across Lapland from the North-North-West. If there's going to be clear sky somewhere, then that's the direction to go. Dive under the clouds and pop out the other side – hopefully. Alright then, let's go, set course to Muonio and continue driving.

The phone rings again. My colleague has checked web cams in the area. Pallas shows clear skies and beautiful weather. I am driving in the right direction. Soon I can see it myself, the snowfall stops and there's blue sky in the North. Keeping going, I have some 45 min left before the start of the eclipse, and I need to set up the equipment, too. Somewhat in a hurry now, it's painful to stick to the 60 and 40-km/h speed limits across Sirkka, I am racing the Moon!

Near the settlement of Pöntsö I find a nice, sunny lay-by, perfect, and I have more than 15 min time. I stop, position the car, set up the tripod, camera, lens, solar filter. Tether the camera to the laptop, connect the camera timer. Finally, I set the iPhone to work as a WiFi hotspot to upload the live images. Argh! Disaster strikes. In all the excitement I have forgotten to check the coverage. Only GPRS available here, not enough speed for uploading images, I need 3G! Quick, pack everything as fast as possible, and keep driving west. Course Muonio. Does the Moon know about 80-km/h speed limits?

Driving with a keen eye on the reception indicator, I come across an elevated area, and soon there are four balls out of five next to the "3G" indicator. Great, now I only need a place to stop before the network fades again. There's a lay-by, and it's sunny, no trees in the way. Stopping and setting up again. It's dot on 11:08, the time of what's called "first contact", when the Moon's beginning to cover the Sun.

Unfortunately, I've lost my race against the Moon, and the very beginning of the eclipse I've missed, but not by much. I set the camera timer to one photo per 20 sec and start my program, which centres the Sun in the final image. This is easy, and this time the technology works just fine. A quick phone call to my colleague confirms, the images are appearing on SGO's web page. Great, we are in business, now the only task is to reposition the camera every 6-8 photos or so. The Sun will move more than 30° across the sky during the eclipse.

But then I see the battery indicator on the laptop, it seems to drain faster than expected. Well, it's cold, and the poor thing has to do image processing all the time. So I switch everything off that's not needed, including dimming the screen. Then I wrap the computer in a warm, black coat, thinking it's own heat will warm it, and the coat will soak up the heat from the Sun. But, hey, the Sun's fading!

At maximum eclipse (pictured above), I finally check the images again – argh! Something in my script has started to do some automagic level adjustment, which leads to the black background becoming bright and noisy, which, in turn, causes the Sun-centering process to fail! Sorry about that, apologies to our viewers. But fortunately I've spotted it now and I am able to compensate by centering the Sun in the camera frame after every image. Some 10 minutes past the maximum, the Sun is bright enough again for my software to work fine, and the rest of the eclipse broadcast goes as planned. Phew!

In the end, the laptop has 30% battery left, and I took some 412 photos in almost continuous blue-sky conditions. Amazing. Suddenly it hits me: I haven't eaten since my small breakfast. Time to pack and head back and find some food – and coffee!

In the evening, back at home, I check the photos with my daughter, and wonder about the strange level adjustment, which happened between 10 min before and 10 min past the maximum eclipse. Finally I am able to track down the culprit: dcraw, the program that converts the raw images from the camera to something that ImageMagick can understand. By default, dcraw adjusts the levels of the images, and this default can be turned off by using option "-W". If only I had known that before the eclipse. Never mind, now I can re-calculate all the images, and see how it should've worked. Hmm... 412 images at 25 frames per second allows for a 16.5-second time-lapse of the eclipse: here it is. A bit wobbly, still, I need to improve my algorithm. But anyway, enjoy!

Thanks to all of you who tuned in to watch the eclipse on SGO's web pages. I hope you liked it. I certainly enjoyed tracking it down for you!

Photos: Thomas Ulich.

No comments:

Post a Comment