When: all night throughout April
What’s special: Messier 63 (NGC 5055), the Sunflower Galaxy in Canes Venatici, sits comfortably with its reputation as one of the great galaxies visible in the night sky at springtime. Arguably, only the crème de la crème of spring galaxies, such as the nearby Whirlpool and Pinwheel Galaxies (M51 and M101) and Messier 81, are superior.
Its cherished Messier designation immediately gives us some clue to its distinction, but it’s only modern-day imaging that fully unveils its grandeur as a very appealing and striking spiral galaxy. It’s big and bright enough to be tracked down and observed through a small telescope and is superbly placed high in the sky on April nights.
How to observe: Messier 63 is located virtually dead centre of Canes Venatici, the Hunting Dogs, just over five degrees north-east of Cor Caroli (alpha [α] Canum Venaticorum), a fine double star. At mid-April, the constellation straddles the southern meridian between midnight and 1am BST (23:00–00:00 UT). The Sunflower is circumpolar (never setting) from UK latitudes, culminating at around 1am at a very advantageous altitude of between 75 and 80 degrees.
Messier 63 shines at magnitude +8.6, bright enough for a pair of 10 × 50 binoculars to show it as a fuzzy patch; sweep 1.5 degrees north of the magnitude +4.7 star 20 Canum Venaticorum. It’s apparent as a galaxy through just a small telescope, while viewing with a ‘scope in the 150mm (six-inch) class reveals the Sunflower’s nebulous, oval-shaped inner halo extending to perhaps 3′ × 1.5′ in apparent diameter.
Well-exposed and processed images show that Messier 63 is a classic example of a ‘flocculent spiral’, a galaxy that lacks a coherent largescale spiral pattern like that of the Whirlpool Galaxy, showing instead many discontinuous spiral arms. Such images show the Sunflower as almost ‘a galaxy within a galaxy’, with tightly wound spiral arms in its aforementioned inner region, surrounded by a much larger outer envelope extending the galaxy to 12′ × 7.6′, where its spiral structure is less coherent and interspersed with numerous dark lanes and pink-red star-forming regions.
A patient observer looking through a 150mm telescope can tease out some of the chaotic inner structure, though perhaps a 250–300mm (ten- to twelve-inch) will be needed to detect some mottling in the envelope, hinting at Messier 63’s fragmented spiral structure.
Messier 63 lies between 26 and 29 million light years from Earth and is a substantial galaxy, spanning a Milky Way-like 100,000 light years. It is a member of the M51 group of galaxies.