Photo by Pittendreigh
M91 was a "missing" Messier object for many years. At one time, it was believed that M91 was a duplicate of the observation of M58. Others suggested M91 was an unrecognized comet of 1781. Most lists now identify M91 with NGC 4548.
HOW TO FIND IT:
M88 is not that hard to spot, but there are no guide stars in the area. I still begin with 6 Coma as my starting point. I slowly scan the area shown on the chart.
Once you have found M88, slowly and carefully scan for M91.
WHAT TO LOOK FOR:
M91 has an irregularly shaped oval.