A Guide to the Spring Constellations — Following the Great Curve into a Sea of Galaxies
Starting from the Big Dipper, follow the Spring Curve and the Spring Triangle and Leo, Boötes, and Virgo unfold in turn. Here is your guide to the quiet spring sky that opens up once winter's brilliance withdraws — and to the sea of galaxies beyond it.
The starting point — from the Big Dipper to the Spring Curve
The guidepost of the spring sky is, without question, the Big Dipper. Around 9 p.m. from April to May, the ladle shape rises high and clear in the northeastern sky with its handle hanging down. Trace the curve of that handle straight on down across the sky — "Arc to Arcturus" — and you reach Arcturus, the first-magnitude star of Boötes. Glowing orange, it is the brightest star in the spring night sky.
Extend that curve further and "Speed on to Spica," and you arrive at the blue-white star Spica in Virgo. This great sweep running from the Dipper's handle to Arcturus to Spica is called the "Spring Curve," and it makes the most reliable landmark when you first go looking around the spring sky.
The Spring Triangle and Leo
Add Denebola, the star at the tail of Leo, to Arcturus and Spica, and you complete the large "Spring Triangle." Spanning the middle of the spring sky, this triangle serves as a reference plane for finding the surrounding constellations.
To the west of the triangle sits Leo, the star of spring, in all its dignity. A shape like a backwards question mark, the "Sickle," forms the lion's head and mane, and the bright first-magnitude star Regulus below it marks the lion's heart. The Sickle really does resemble the front of a lion, so even a first-time viewer can trace it easily. In Greek myth this lion is the Nemean monster that Heracles slew with his bare hands.
A sea of galaxies — spring deep-sky objects
With few bright stars, the spring sky can look a little empty — but in return, we are looking out beyond the disk of our own galaxy (toward the galactic north pole), so this is the season when distant external galaxies show up in unusual abundance. Behind Leo lies the "Leo Triplet (M65, M66, NGC 3628)," and between Virgo and Coma Berenices sits the "Virgo Cluster," a gathering of thousands of galaxies. Most appear as faint cotton-wool smudges in a small telescope, yet each is a vast city of stars tens to hundreds of millions of light-years away.
There is plenty to enjoy with the naked eye or binoculars, too. Under a dark sky you can trace the "Croc's Eye Galaxy M94" in Canes Venatici, or hunt out the galaxies between Leo and Ursa Major with binoculars, and Coma Berenices itself is a faintly glowing cluster (Melotte 111) that appears as a hazy knot of stars on a clear night.
Best times and directions to observe
The spring constellations climb high from the southeast into the southern sky in the early-to-late evening from late March through May. Around 10 p.m. in April, Leo stands high due south and the Spring Curve arcs handsomely across the eastern sky — the best conditions for observing. Arcturus and Spica show well even in the city, so use these two to get your bearings before widening your gaze to the fainter constellations.
The spring galaxies, however, are all faint and barely visible under the light pollution of a city. If you are after galaxy-hunting, it matters most of all to choose a dark sky away from the city around the new Moon. Spring air can be somewhat unsteady, making stars twinkle heavily, so wait for a calm, transparent night and you will meet a far crisper sky.