NGC 2903 in Leo: the best galaxy not in Messier’s list?

NGC 2903 is one of the best galaxies in the entire sky and is a baffling omission from Charles Messier’s catalogue. Image: Adam Block.

It’s not often that one can assert that a deep-sky object within a given constellation that’s without a Messier tag can, at the very least, rival one that does. Many observers propose that NGC 2903, a superb spiral galaxy in Leo that’s a major highlight of the spring sky, fits the bill, matching up well to marvellous Messier 66 (NGC 3627) or indeed any of the other galaxies, Messier-designated or otherwise, found in Leo.

NGC 2903 requires a merely modest aperture to snare it at its easily to find location. Once found, it yields a fair degree of detail through a moderate-aperture telescope and makes for a fantastic imaging target. NGC 2903 is perhaps the most notable and perplexing omission from the Frenchman’s ubiquitous catalogue and, as such, is not to be missed.

NGC 2903 is advantageously located for observers at mid-northern latitudes, in northern Leo. Look for it just south of Alterf (lambda [λ] Leonis), the fourth-magnitude star marking the Lion’s mouth on historical star charts.

How to observe

The fantastic constellation of Leo, the Lion, led by first-magnitude Regulus (alpha [α] Leonis), is at the vanguard of the major constellations of the spring sky.

The stars that form the Lion’s head, principally magnitude +3 epsilon (ε) Leonis, Rasalas (mu [μ], mag. +3.9) and Alterf (lambda [λ], mag. +4.3) hit the southern meridian at 10pm GMT, mid-March. Epsilon and Rasalas also form the northernmost section of the curving portion of Leo’s famous ‘Sickle’ asterism of six stars, including Regulus and Algieba, which together are popularly likened to a backwards question mark. 

NGC 2903 is located just 1.5°south of Alterf and culminates at a very healthy altitude of around 60°. It can be observed until about 3am GMT, giving it an overall mid-month observing window lasting around seven hours.   

NGC 2903 shines at magnitude +8.9, making it marginally brighter than Messier 65 and 66, and spans a generous 13’ x 6.6’. It should be apparent as a tiny smudge in 10 x 50 binoculars and through a 80mm (~three-inch) telescope on a transparent and moonless night in the countryside. A 100–150mm (four- to six-inch) telescope under high magnification can reveal a bright nucleus and a surrounding mottled halo, which is the galaxy’s largely unresolved spiral arms, superbly seen traced by young, blue star clusters and pinkish star-forming regions in deep amateur images.

Hubble Space Telescope’s take on NGC 2903. Image: ESA/Hubble & NASA, L. Ho, J. Lee and the PHANGS-HST Team.