Here’s a fine image of one of the most famous galaxies in the sky, the Whirlpool Galaxy in the constellation Canes Venatici. This image of the Whirlpool, also known as M51, was taken by amateur astrophotographer Jeff Johnson from Las Cruces, New Mexico with a Takahashi TOA-130F telescope and cooled QSI CDD camera. The integration is long enough, and the post-processing deft enough, that you can see a handful of far more distant galaxies in the background of this image.
As you can see, there are two galaxies here. The smaller galaxy, NGC 5195, through gravitational interaction, has triggered a wave of star formation in the larger M51. That’s why the Whirpool’s spiral arms are so prominent and well defined. You can see many pink nebulae flecking the blue spiral arms, and a splotch of displaced stars between the two galaxies. There’s a lot of physics going on in this galaxy pair: star formation, density waves in the spiral arms, stellar dynamics, even the occasional supernova (two in the last 8 years). So astronomers love to study this system to learn more about galaxy formation and evolution.
The M51 and NGC 5195 are the showpieces of a rich area under the “handle” of the Big Dipper. Both can be seen in the same field of view just 3ºsouthwest of Alkaid, the star at the tip of the Dipper’s handle. Lord Rosse was the first to glimpse the spiral structure in M51 with his massive telescope in the Irish countryside in the mid-19th century.
While photographs of M51 show blue spiral arms and clots of pink nebulae where new stars are born, the view through a telescope is far more modest. It takes at least an 8-10 inch scope to even glimpse the spiral structure visually in dark sky. If you’re in the city, sadly, you’ll only see the fuzzy nuclei of each galaxy. The Whirlpool, like many face-on spiral galaxies, was once thought to be a new solar system forming within our own galaxy. When Edwin Hubble established the distance to the Andromeda Galaxy in 1929, astronomers understood these objects were separate galaxies in their own right. M51 is some 23 million light years away and spans 50,000 light years, about half as much as our own Milky Way.
Thanks to Jeff Johnson for this “look” through his telescope. You can learn more about this image and Jeff’s work here…