M51 - NGC5194 - Whirlpool Galaxy  
Canes Venatici

Interacting grand-design spiral galaxy, one of the most famous spiral galaxies in the sky.
It is located at a distance of approximately 23 million light-years in the constellation Canes Venatici. The galaxy and its companion (NGC 5195) are easily observed by amateur astronomers, and the two galaxies may even be seen with binoculars.

he Whirlpool Galaxy was discovered by Charles Messier on October 13, 1773. Its companion galaxy, NGC 5195, was discovered in 1781 by Pierre Méchain. It was however not until 1845 that the Whirlpool became the first galaxy to be recognized as a spiral. This was achieved by Lord Rosse employing a 72-inch reflecting telescope which he constructed at Birr Castle, Ireland. In 2005 a supernova (SN 2005cs) was observed in the Whirlpool Galaxy, peaking at apparent magnitude 14. Sometimes M51 is used to refer to the pair of galaxies, in which case the individual galaxies may be referred to as M51A (NGC 5194) and M51B (NGC 5195).

With derived estimate of 23 Mly distance, and an angular diameter of roughly 11.2′, we can infer that M51's bright circular disk has a radius of about ~38 kly. Its mass is estimated to be 160 billion solar masses. Compared to 100 kly diameter of the Milky Way, M51 has about half its size and mass.

Decades ago, it wasn't known for certain if the companion galaxy NGC 5195 was actually a true companion or rather some other galaxy passing at a distance. The advent of radio astronomy and subsequent radio images of M51 unequivocally demonstrated the reality of the interaction.

Recent simulations bear out that M51's spiral structure was caused by NGC 5195 passing through the main disk of M51 about 500 to 600 million years ago. In this model, NGC 5195 came from behind M51 through the disk towards the observer and made another disk crossing as recently as 50 to 100 Myrs ago until it is where we observe it to be now, slightly behind M51.

A black hole surrounded by a ring of dust exists at the heart of the spiral. The dust ring stands almost perpendicular to the relatively flat spiral galaxy. A secondary ring crosses the primary ring on a different axis, a phenomenon that is contrary to expectations. A pair of ionization cones extend from the axis of the main dust ring.
Technical details:  
Guadalix de la Sierra - Spain
18/03/2007 (dd/mm/yyyy)
Meade SC8" f/10
f/6.3 Meade
No filter
Vixen GPD2 Autostar Meade
Nikon D50
4x300s+ 1x400s+ 1x500s+ 1x600s@ISO1600
Guiding tube:  
Skylux 70/700 f/10
Guiding camera:  
Celestron NexImage
Guiding software:  
Four DARKS stacked @ISO1600, 26 minutes total, 2ºC.  
Very noisly picture, mostly due to limited number of darks applied and use of 1600ISO. Anyway, the D50 Nikon used in this picture denotes not too much noise @1600ISO.  


All Contents Copyright by Jaime Fernández and Copyright of their respectives owners. Text mainly extracted from Wikipedia.
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