April 2002

The following images were obtained with an SBIG ST-7E CCD and a Meade 10-inch LX200 Schmidt-Cassegrain telescope on April 21, 2002 UT from the Steward Observatory 40" dome atop Mt. Lemmon, AZ (altitude = 9300 ft.). Images were acquired and processed using MaxIm DL/CCD V2.12. The imaging employed an f/6.3 focal reducer yielding an effective focal length of 64 inches and north is at top, east is to the left in all of these LRGB pictures. All celestial coordinates are for epoch J2000.0.

M51 (NGC 5194) The "Whirlpool" Galaxy. RA = 13h 29m 53s; Dec = +47d 11' 48". This is one of the most famous "face-on" spiral galaxies in the sky, and along with its northern companion galaxy NGC 5195 form a fine galaxy pair in the constellation of Canes Venatici. These stellar systems are estimated to be about 10 Mpc away and have radial velocities of about 550 km/s in approach. The pair shows a good example of the range in colors encountered in galaxies. The pronounced spiral arms of M51 are blue, indicating that hot, young stars dominate the light emitted in the disk of the galaxy. Also notice the pronounced dust lanes associated with the arms. In contrast, the nuclear bulge of M51 and NGC 5195 are more yellow in color. Older, redder stars are more dominant in these regions. Some of the reddness of NGC 5195 is also caused by the dust associated with the disk of M51 that is in front of the smaller companion galaxy. M51 is over 30 kpc is diameter.

M82 (NGC 3034) RA = 09h 55m 54s; Dec = +69d 40' 57". This famous "irregular" galaxy is a bright source of infrared light and together with M81 (NGC 3031) forms one of the most famous galaxy pairs in the sky. Many dust lanes within the galaxy can be seen and it is the heating of this dust by the large number of young stars in this system that results in its high luminosity at near-infrared wavelengths. The object lies in the constellation of Ursa Major (The Big Bear) and is thought to be about 2 Mpc distant.

Both color images of M51 and M82 were formed by combining three 20-minute unbinned exposures using a "clear" filter (+ IR blocking filter) with three 10-minute exposures using blue, green, and red filters. The CCD was binned 2x2 for each of the colored filters. The total exposure time for each composite picture was (3 x 20 min) + (3 x 10 min) + (3 x 10 min) + (3 x 10 min) = 150 minutes.