Crescents in April 2012

Version 23.4.2012 Martin Elsaesser,

Young crescent on 21. April

The young crescent of 21. April was very difficult, as conjunction was very close at only 2.2° elongation. We had good clear skies before noon, but did not attempt to see the crescent due to the extreme closeness to the sun. Around noon, the skies started to get more cloudy, with layers of high altitude haze, so we did not expect any chance to observe in the evening. The clarity of the air was excellent though, due to the wind and dry air.
Unexpectedly, around 17:00 a huge gap in the clouds started to form from a local weather phenomenon called the "Föhn", so i hurriedly set up a crescent imaging telescope at the public astronomical observatory in the center of munich, not having the time to go to a better location. I also asked two visitors from Oman to join me, as we had been testing the crescent telescope for a few days.

After setup of the instrument on a neighboring roof we aligned the goto-system on the sun, adjusted focus by looking at jupiter and then sent the goto system to the position of the moon. We moved the instrument slighly downwards, to get the actual crescent into the center of the field of view. We used the prototype of a spezialized software to automatically adjust camera settings and do the real time image processing, so we mainly stood around without much to do, staring on the screen to look for the crescent. We could not clearly see the crescent on the screen, but a quick review of the automatically saved images showed a thin arc of light moving among the haze and noise, so we rejoiced.

Alas, it quickly became clear that the gap in the clouds was only temporary and that we would not be able to observe until sunset. We first found the crescent around 19:05 (UT+2), at an elongation of 4.23°, an altitude of 14°, about 75 minutes before sunset. We lost it to the fast-moving clouds around 15 minutes later, about one hour before sunset.

When inspecting the captured images later, i found no single good, convincing image. So i cut about 60 images from the stream and combined them to a short video, which clearly shows the moving arc.

crescent of 21. april
The young crescent around 19:07, as short video cropped from the full size images. It takes some time for the 10MB animated GIF to load, but when it plays at full speed and the crescent can be seen.

crescent telescope
The crescent telescope on the roof, with a clear view of the mountains to the south in the background, some 50km away.

crescent telescope and sky
Crescent telescope and sky, around 18:58, shortly before we found the crescent.

crescent of 23. march
Telescope and sky around 19:18, shortly before loosing the crescent in the clouds.

So, a nice, if short observation of the crescent at very small elongations. Sadly, the clouds prevented us from following it till after sunset and we also could not try visual observation after sunset, though the telescope would have been ready for it.

Young crescent near Jupiter on 22. April

The young crescent passed Jupiter on the evening of 22. April. Both objects together formed a nice sight. I could first spot the crescent around 18:40 with a small telescope at 50x, some 90 minutes before sunset in good blue skies. Later, the crescent could be easily seen with the naked eye.

sky and telescope, during visual observation
The visual crescent telescope pointing at the blue sky.

crescent and jupiter
Crescent and Jupiter after sunset, 300mm lens.

crescent and jupiter
Crescent and Jupiter after sunset, 300mm lens, contrast stretched. This is NOT the visual view, but shows earthshine.

crescent and jupiter
Crescent and Jupiter after sunset, 300mm lens, contrast stretched, color saturation increased. This is NOT the visual view.

last view of crescent and jupiter
Last view of crescent and jupiter before the clouds.

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