A few times in the past I have seen charts of the dark sky quality for astronomical use. Especially during a visit of the University astronomy department I had the chance to talk with one of the facilities operators. This made me curious about how they quantify the night sky quality.
Upon further research I found the widely used Sky Quality Meter by Unihedron. It is a small box measuring the sky brightness by means of a light sensor with corresponding frequency output. When I could find a distributor selling these sensors for a good price, I was up to building my own one. My concept was to use a arduino style micro controller and build a sky quality meter together with weather data (temperature, pressure, humidity) recording device. The device should save every 10-30 seconds the data collected. And it should last for at least one whole night running on a small(er) battery like AA or 18650 lithium type.
The hardware part was quite easy to accomplish. I simply had to connect a couple of wires from the micro controller to the sensors and other components. The harder part was to create a proper software, fulfilling all my needs. I had to find a way to 1) cope with the frequency range of 0.01Hz to 1MHz 2) fit all the code within the small memory 3) calculate sky quality and calibrate device to a reference device
Luckily, apart from a reasonably well described device on the Unihedron web-site, I could borrow one Sky Quality Meter from a fellow astronomy club member. So I had a reference device to compare and calibrate my device.
Here is the test setup. The readings are already very close to the original device!
It is always frustrating to see good weather pass without the opportunity to do some photography – especially astro-photography. So even if time does not permit a trip to the darker spots in reasonable distance from my home, it is worth a try to setup the telescope on the balcony.
This time, clouds cleared throughout the day (and happend to reappear before midnight). So I had to take the chance to spot Comet C/2018 Y1 Iwamoto. Unfortunately, I was unable to spot the comet through the eyepiece. The sky was far too bright (approximately 18mpss) watching straight over the citys light dome and having a 60% illuminated moon shining bright. Fortunately, through the camera I could make out a smudge, being brighter than the sky.
Processing the 180s subs with 1 hour total exposure time, I could achieve this result (compare to the unprocessed image!):
Image is a composite of 2 stacks (one aligned on stars, second aligned on comet). The comet moved more than 1.5 degrees during the 1 hour capturing time! Above the comet: NGC 2903 (mag 9 galaxy) At left: NGC 2916 (mag 12.1 galaxy)
Imaging setup: 800mm f/4.0 Newton, Sony A6000 full spectrum modified, UV/IR block filter, UHC filter, coma corrector (at wrong distance). 20x 180s @ ISO800, darks and flats Conditions: +2°C, 60% moon, 18-18.5mpss sky in suburban location (with ample street light)
I had a bit of time to experiment with an H-alpha filter at home. Conditions are limiting astro-imaging as my balcony faces south. Living in the northern outskirts of a city, all the sky visible is significantly affected by city lights. This night, the sky was somewhat OK, reaching up to 18.7 to 19.5 mag/arcsec².
Using narrow band filters, like an H-alpha filter, the majority of the city lights may be cut away. This image (not perfectly focussed) shows, what is possible. It is a result of 12x240s, captured at ISO800 with my modified Sony A6000…
After 2 weeks of thick cloud coverage, I had the chance to spend the evening at the observatory. Actually I jumped in to hold the guided tour this evening… As there was almost full moon and some cloud coverage (which got steadily thinner) I played a bit around with the setup. I thought – deep sky at full moon is a waste of time. But how about the comets 46/P Wirtanen and 38/P Stephan-Oterma? How brigth are the comets still? Would they shine through the moon lit sky? Well… I could not make out Stephen-Oterma. But Wirtanen was barely (in)visible. I had some other tasks to do, so I attached the camera to the scope and let it run to see, what may be gathered under these conditions. Despite of the Moon and the corona of Moon, a little bit of the comets was still possible to process from 90 minutes of total exposure time each:
In the night of the 2018 Perseid meteor shower maximum I was out to the mountains for a fantastic view of the stars. I also setup my slider to capture the milkyway moving across the sky… Well I did not expect that amount of humidity. The camera got completely covered in dew and I forgot to bring my dew heater. So the video only lasts for 3 hours time, until all was soaking wet…
During a telescope meeting in mid June 2018, set in the Austrian mountains I created the following two hyperlapses. The milky-way including some clouds passing over is a fantastic view. The transition from night to the first light of the morning sun is non the less a pleasure!
Actually, I shot the footage of this timelapse more than 3 years ago. Though I kindof “lost” the images on my backup storage and forgot about it. A couple of days ago, I stumbled upon the files…
I sent a few days at a farm in northern Sardegna, Italy during a late August full moon. The terrace of the main building offered this splendid veiw of the countryside and pigs enclosure (you may see a few pigs running around at the end of the video). The full moon cast a shadow all night long, while the stars pass around Polaris.
The timelapse was shot between 19:44 and 08:53, covering 13 hours with 777 single exposures.
Post processing in Lightroom and LRTimelapse
My saturday night astrophotography session (see last post) got some attention in local news. Two folks from Kleine Zeitung accomanied me and a friend to the observing location. They created a video report, showing us freezing the ***** off for a nice photo.
Kudos to the journalists, as they endured the -10° until 2:30am!
This weekend is the perfect viewing opportunity for Comet 46/P Wirtanen:
First, the comet is closest to eart by less than 0.08 astronomical units (distance from earth to the sun), which is approximately 30 times the distance to moon!
Second, the comet passes very close to the open cluster M45 – the Pleiades.
And third, it is still an early moon phase. This means that from midnight on, the night will be really dark!
I was eagerly waiting for this view. Though current weather conditions in central Europe did not promise anything suitable for observations until 2-3 days ago. Saturday night showed increasing patches of open skies…
Finally, Saturday in the late afternoon, the sky cleared up. So all was a go for observing!
At -11°C conditions were cold but good for astro photography. Recent precipitation left some humidity in the air, reducing air transparency a bit. What caused some trouble was, a frost cover building up on all the equipment (photos will follow)…
Here are the results of a loooong night up in the mountains:
The following timelapses show, how much angular distance the comet 46/P Wirtanen makes, when closest to earth. From my data I see approximately a stunning 1° during 4 hours!
85mm photo lens with 1.5x crop sensor
93 exposures, each 60 seconds long (93 min total)
200mm photo lens with full frame sensor
160 exposures, each 90 seconds long (240 min total)
715mm/f7 APO with 1.5x crop sensor
71 exposures, 30 and 60 seconds over 80 min
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