Index of /~jhollan/dirs/light/luminance/tempel

	Name	Last modified	Size	Description
	Parent Directory		-
	tempel.zip	2005-07-08 17:58	21M	all directory zipped
	info_d.txt	2005-07-07 20:48	3.9K	results overview
	overview_r2l.txt	2005-07-07 20:48	243	jhead (exif) info
	11d.jpg	2005-07-07 19:51	70K	image - darkframe
	07d.jpg	2005-07-07 19:51	67K	image - darkframe
	04d.jpg	2005-07-07 19:51	67K	image - darkframe
	11g128.jpg	2005-07-07 19:29	1.2M	luminance grid, large
	11_128.td	2005-07-07 19:29	14K	tabelled photometry
	11_128.eps	2005-07-07 19:29	3.2K	grid in PostScript
	04g128.jpg	2005-07-07 19:29	1.2M	luminance grid, large
	04_128.td	2005-07-07 19:29	14K	tabelled photometry
	04_128.eps	2005-07-07 19:29	3.2K	grid in PostScript
	07g128.jpg	2005-07-07 19:28	1.4M	luminance grid, large
	07_128.td	2005-07-07 19:28	14K	tabelled photometry
	07_128.eps	2005-07-07 19:28	3.2K	grid in PostScript
	11g.png	2005-07-07 19:26	4.8M	luminance grid
	11.png	2005-07-07 19:26	133K	colour coded luminan.
	11.td	2005-07-07 19:26	239K	tabelled photometry
	11.eps	2005-07-07 19:26	38K	grid in PostScript
	04g.png	2005-07-07 19:26	4.6M	luminance grid
	04.png	2005-07-07 19:25	133K	colour coded luminan.
	04.td	2005-07-07 19:25	286K	tabelled photometry
	04.eps	2005-07-07 19:25	38K	grid in PostScript
	07g.png	2005-07-07 19:25	3.8M	luminance grid
	07.png	2005-07-07 19:25	133K	colour coded luminan.
	07.td	2005-07-07 19:25	241K	tabelled photometry
	07.eps	2005-07-07 19:25	38K	grid in PostScript
	11.txt	2005-07-07 19:09	361	jhead (exif) info
	04.txt	2005-07-07 19:09	361	jhead (exif) info
	07.txt	2005-07-07 19:08	361	jhead (exif) info
	info.txt	2005-07-03 22:44	4.1K	original camera info
	11.jpg	2005-07-03 22:43	1.1M	camera-stored jpeg
	07.jpg	2005-07-03 22:40	1.1M	camera-stored jpeg
	04.jpg	2005-06-28 23:13	1.1M	camera-stored jpeg

Sky over Brno Observatory, June 28 and July 3 and Comet Tempel 1

The air in the first night was very transparent, this leading to the minimum luminance near zenith about 2.1 mcd/m² (2.1 mnt, i.e. two millinits) and just about three millinits at the position of Tempel 1 comet (just over Spica, the star which is faintly visible left from Jupiter). Let's remember that these two millinits mean a sky which is ``just'' eight times brighter than the natural one...

The second night was an average one. Minimum luminance near zenith was 3.2 mnt, and close to Tempel 1 it was six millinits. This is way too much.

No wonder the comet was invisible. Having about 10 mag and some 2' diameter, its luminance should be about one millinit. Within the millinit realm, human eye can not perceive a small spot which is just by 1/6 brighter than the surroundings. Quite probably, it would be still invisible at ``3mnt sky'' (being just 1/3 brighter). It could become to be visible just in those sites, where the surrounding sky has no more than one millinit (the comet having then twice the luminance of the sky). Of course, in our country the comet is so low, that it is at least one magnitude fainter due to extinction, so the prospect to see it is even worse.

For a 3mnt sky the comet sized two angular minutes should have nine magnitudes (including extinction) to become visible. On a 6mnt sky, 8 mag would be needed. However, after Deep Impact it did not brighten at all that much (it turned just several decimagnitudes less faint).

Similar computations can be done with my programme lum, as for 8 mag:

lum m2 8 

The equivalent of Luminance expressed by a star of faintness of
 8.00 mag  defocused to a circle of angular diameter of   2.0 minutes
       means a Luminance of some
                                   0.00603 cd/m^2

In fact, the inner part of the comet could be still seen under three-millinit sky with a 50cm telescope, assuming that the inner part has a much higher luminance. If a circle of 0.3' diameter would have 12 mag, its luminance would be 6 mnt allowing it to be perhaps noticed when magnified 100× (being then half a degree large). Still, it would be no easy task, as the luminance changes continuously from the comet centre to the ``normal'' sky.

Illumination of the horizontal surface is another result obtained from the images. It was 9 mlx (almost one centilux) on June 28, and to 17 mlx on June 3.

For any interpretation of the luminances, the extinction is to be determined. This is possible ``manually'' from the star images, but should be preferably done by some future software instead.

Any brighter segment due to astronomical twilight over northern horizon was completely invisible. Image times are UTC + 1 h 02 min, differing just 4 min from the local time, so the sun from Brno was at -17 degrees by the June image and at -16 degrees by the July ones.