An Urban Supernova
A new supernova, SN 2011dh, has appeared in M51 that is at this time (June 2011) visible from typical urban and suburban skies using moderately sized telescopes. This is a unique opportunity to see a star from another galaxy without having to travel to a dark-sky site. It is rare for an extragalactic supernova to appear as bright as this, and even rarer for it to appear in a relatively well known and easily located galaxy such as M51. And not only that, but it is well position for observing in the early evenings, making it an easy target in later June when the moon is well past full. Even with a nearly full moon, I've found SN 2011dh easy to see with my 10 inch Dob. I've generated some finder charts to make it easy for anyone to locate this supernova....
At the time I write this, reports place SN 2011dh somewhere between magnitudes 12.3 and 12.6. This puts it within easy reach of an 8 inch (200 mm) aperture telescope in even urban areas. A 6 inch (150 mm) telescope should suffice if your sky isn't heavily washed-out by light pollution. While M51 is easy to locate, the galaxy itself is notoriously difficult to see in light-polluted skies (see my article on Elusive Galaxies), To help locate SN 2011dh, I've generated a set of finder charts using the AAVSO Variable Star Plotter.
I made four charts at standard AAVSO scales A, B, C, and D. These charts are all oriented with north on the top and east on the left. If you prefer a different orientation, you can use the Variable Star Plotter yourself, just enter “SN 2011dh” as the variable star name.
On the A chart, I labeled Alkaid (η UMa), the last star in the handle of the Big Dipper. I've also labeled three stars “A”, “B”, and “C” on all of the charts (only “A” fits on chart D) to help you navigate the scale changes across charts. These three stars form a triangle visible in finder scopes that is commonly use to star-hop to M51. As the charts clearly show, SN 2011dh is relatively easy to locate because there aren't any other 12th magnitude stars in the area. On the D-scale chart, the "stars" labeled X and Y are actually the central cores of M51 and its companion, NGC5195.