The picture below was made by pointing the camera at the north celestial pole and leaving it taking photographs continuously all night. Three of the resulting pictures were removed as they showed aircraft crossing the scene, and the last few hundred were removed because the sky was brightening, clouds came over and the light saturated the camera. The resulting pictures were combined in K3CCDTools using the if-lighter option. This option only adds a pixel into the stack if it is brighter than the pixel in the stack. This prevents the images of the stars being averaged with dark sky.
|The polar stars rotating about the North Pole. Move your mouse pointer over the image to see superimposed on this image, a single frame from the middle of the sequence with some of the brighter stars labelled. In that image I have given a- and k-draconis their full designation to emphasise that these stars are part of the large constellation of Draco and not part of the adjoining Ursa Major.
The pictures were taken using a DFK 21AF04 camera with a 3.5mm lens intended for a security camera. It was set to take 27.5-second exposures every 28 seconds throughout the night, starting at 21:40 UT, by which time the sky was dark, until 04:35 on the morning of 17 Aug 2018. Of the 889 pictures collected, only the first 530 were usable; at about 01:15 cloud came over and, by the time it cleared at about 03:15, the sky had become so bright that the camera was saturated.
Camera: DFK 21AF04
Lens: Avenir CCTV lens 3.5 mm f/1.4
Exposure: 27.576 sec, repeated every 28 seconds.