Monthly Archives: August 2013

A colorful nebula

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The Dumbbell Nebula (M27) in constellation Vulpecula.

A planetary nebula represents the final stage in a smaller stars life cycle, such as our own Sun. Near the end of its life, the star enters a phase of Helium shell burning that causes the star to blow away its outer atmosphere with strong stellar winds, over a period of about 10,000 years. Finally, only the central white dwarf star remains, with no more exciting prospects than to spend the next billion years slowly cooling off.

This is though luck for the star, but the nebula that is formed from the ejected material makes for a pretty picture from afar. The object is still expanding at about 30 km / second. The red color is from hydrogen gas emitting in the H-alpha region. The blue and green in the center should stem from oxygen, although the lack of actual green probably indicates that I need more practice at color-balancing.

Apart from that, however, it is a true color image taken in the visual spectrum. It was composed from 150 individual frames exposed for 10 seconds each, giving a total exposure time of about half an hour. A 0.5 x focal reducer was used.

I am quite happy about the result because I did not have too much luck with faint nebulous objects until now, and the individual frames did not show much appreciable signal before processing. Now that I got it to work in principle I will try going for longer total exposures, that should get rid of the noisiness that is still quite apparent in this image.

 

Shadows of Montes Caucasus

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Todays attempt to improve on previous ISS pictures failed due to last minute cloud cover. However, prior to that the waxing crescent moon presented an attractive target in the dusk. Near the terminator we see Montes Caucasus casting long shadows on Mare Imbrium. The largest crater in the image – Aristoteles – has a diameter of 87 km.

Tomorrow, the ISS should make a day-time pass in front of the Moon from here. I’ll try to catch that if I get a chance.

New perspectives on ISS

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I took another shot at ISS last night and successfully captured it on numerous frames. I stacked a handful of frames for each of the three main perspectives and composited them into a single image:

(If you view this on a mobile device you may need to increase the display brightness somewhat to see the fainter detail)

This pass at 4:05 AM over The Hague was not directly overhead, rather, with a maximum altitude of 44°, it provided a more “sideways” view of the station. Also the slower apparent velocity allowed for more relaxed manual tracking, and resulted in more individual frames of the station per pass over the chip.

I originally went out early to image Venus in the hope of at least recognizing the phase, but didn’t get satisfactory results – I accidentally used additive binning which caused Venus to be overexposed in all frames. But I feel these ISS shots adequately compensated my disappointment.

I’ll try Venus another time, although I fear I am generally not in a hopeful position for success with that lady: at latitude 52°N, Venus is already less than 10° above the western horizon at sunset, and over the sea at that.