Another Venus crescent

The forecast promised a few clear hours in the evening, so I set up the 8″ scope. Cloud cover remained almost complete, but Venus managed to peek through a few times:

Since these appearances were short and variable I did not manage to configure good camera settings and most frames were overexposed. In the end I deliberately used 300 frames taken through lighter clouds and therefore diminished.

Venus Crescent and other Galileoscope targets

It has been a while since the last post due to other commitments, an inconsiderate flu, and travel. So long, in fact, that Venus has moved appreciably in its orbit, passed greatest eastern elongation and is now distinctly crescent-shaped:

This quick image was taken with Galileoscope near sunset, with Venus about 10 degrees above the horizon and piercing through significant cloudiness. Due to bad seeing and general featurelessness of Venus it is unlikely that using the larger scope would have made much of a difference.

I’ll use this opportunity to also post two images taken last month using the Galileoscope: An attempt to capture the ISS by simply following it with the hand-held scope while taking live video …

… and a morning view of the waning gibbous Moon in daylight:


Waning Gibbous Venus

I finally managed to get a recognizable look at Venus. The gibbous phase is clearly visible as Venus progresses towards its greatest eastern elongation that will occur on November 1st (at that time it will have maximum distance from the Sun and appear “half lit”). As Venus is always hidden under 100% cloud cover, there are no surface details visible even at the best of times.

The image was taken around sunset when the sky was still very bright to catch Venus as high as possible, but even so Venus was already very low in the sky (~10° altitude from 52°N). Due to the short exposure times, the sky appears mostly black anyway. Here is an unprocessed sample frame for comparison:


As can be seen, imaging through that much atmosphere severly degrades image quality. Turbulence in the air smears the image, and dispersion (due to wavelength-dependency of refraction) turns objects into little rainbows (in fact, for bright objects the atmosphere can be used as a poor man’s spectograph).

However, stacking multiple of these short exposures averages out some of the distortion, while the rainbow effect can be diminished by aligning all color channels individually. I took about 20,000 frames at 0.5 ms exposure over a period of about 4 minutes, 10,000 of which were used for the image presented here.

Saturn is currently located a little to the upper left of Venus (for Nothern Hemisphere observers). It is certainly not a reasonable time to image Saturn, but it was the logical target after Venus:

A colorful nebula

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

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

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.

Waxing crescent moon with Galileoscope

I still didn’t get an adapter to mount the Galileoscope, but improvised a bit today to take an image of the waxing crescent moon. This was taken at dusk when the sky was still fairly bright, but it still appears black due to the short exposure time.

My main plan for the evening was actually to catch ATV-4 zipping across the Moon as predicted by Heavens Above, but I didn’t even see the space craft. I suspect the prediction was out of date due to all the maneuvering taking place the day before the planned docking.

Fairly decent ISS shot

This is my second attempt at an ISS shot. It certainly turned out better than the first:

Well, technically it may have been the third attempt because there were two passes this night and I botched up the first (tracked diligently but forgot to take pictures …).

I track manually while continually acquiring images and try to keep ahead of it in the finder, then let it drift over the chip area. One eye needs to stay glued to the finder while the ISS moves from near the horizon to almost overhead. It is probably the most sportive activity I engage in, as it requires to slowly shift from one yoga-like half-crouch position to the next for several minutes.

Currently ISS is trailed in its orbit by Albert Einstein, the automated transfer vehicle ATV4. It passed about 10 minutes later and I tried to take pictures of it, but as it is much smaller it remained an unimpressive dot.


Six moons and a planet

In the race to take best resolution images of Jupiter and Saturn at highest powers and frame rates, the moons often get neglected. Personally, I do like to see entire systems with their ever-changing view.

Of course, the moons are fainter than the planet so usually the planet will be terribly overexposed when the moons are imaged. At the cost of photometric unscientificness, this can be overcome by merging multiple exposure times in a single image. Here is one of Saturn that shows six of its moons, including faint Hyperion at around 15th magnitude.

And because that is really just a lot of dots without context, here is an annotated version

The process I use is to take a few short exposure frames as for normal planetary images, then one or two longer exposures, then repeat. Each of these frame sets is combined into a meta-frame by some scripting fu that attempts to pull signal from the longer exposures into the dark areas of the shorter exposures. The composite frames can then be stacked as usual. I made a similar one in March for Jupiter

For that one I actually took a gazillion frames over three hours in the hope of making a video out of it once I fully automate the compositing process. Unfortunately I seem to be building up a bit of an image processing backlog. Even now, while I’m trying to reduce the pile, the sky turned clear and the telescope is collecting data outside – argh!