Asterisme
Et asterisme er inden for astronomi en betegnelse for et mønster af stjerner på himlen, hvor der ikke er tale om et officielt stjernebillede. Af kendte asterismer kan nævnes Karlsvognen og Sommertrekanten.
Det er også betegnelsen for en stjernelignende formation i visse safirer (og tilsvarende i rubiner); disse kendes af samme årsag som stjernesafirer og stjernerubiner.
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Forfatter/Opretter: The original uploader was DannyZ at engelsk Wikipedia., Licens: CC BY-SA 3.0
Credit: Till Credner, AlltheSky.com
Collinder 399 (Brocchi's Cluster)
Source: http://www.allthesky.com/constellations/vulpecula/constell.html
USED BY PERMISSION under the terms of the GNU Free Documentation License (GFDL).
I am uploading this image file again at this time in order to make certain that everything has been done properly in regard to permission and licensing. The image itself has not changed since the original upload in April 2005, but hopefully the documentation will be improved now.
The copyright holder of this image is Till Credner. His website (and the source of this image) is: http://www.allthesky.com/ . On April 23, 2005 I wrote to Till requesting permission to use the image on Wikipedia under the terms of the GNU Free Documentation License (GFDL) using the sample letter provided by Wikipedia at that time. On April 25, 2005 I received a reply granting permission to use the image in the size displayed at: http://www.allthesky.com/constellations/vulpecula/c399.jpg .
On September 9, 2007 I forwarded my complete correspondence with the copyright holder to "permissions-en AT wikimedia DOT org" as directed on the upload page so that "the Wikipedia Foundation has a record of the license in case questions should arise at a later time about the permission for this image"
The technical details about the image as given by the copyright holder are as follows:
This image is a magnification of a 3° x 3° field from an original wide-field image. The original image was obtained by Till Credner on August 8, 1999 at 23:57 UT from the Hoher List Observatory about 100 km SW of Bonn, Germany. It was exposed 35 min on Kodak Royal 400 Select with a f=50mm 1/4.0 lens. The field of view of the original image is 39° x 27°. The image was obtained with a usual mechanic camera and lens of normal focal length (50mm). Guiding was done on a Super Polaris mount. The conventional photography was digitized to 2048 x 3072 pixels and a color depth of 3 x 8 Bits. Digital image processing improved the quality of the image dramatically. The main steps were the subtraction of the sky background and following contrast enhancement.