The stars are wonderfully social: Most of them belong to double or multiple systems, and many travel together in large communities known as open clusters. These celestial gatherings are among the loveliest sights in the sky. And contrary to the common assumption, you do not need a telescope to appreciate them. Binoculars or even a pair of eyes will do, as long as you know where to look.
This month Jupiter points the way to one of the most storied star clusters: the Beehive. Step outside around 9 or 10 p.m. on a clear night. High up, creamy Jupiter outshines every star in the sky. Its steady gleam—planets do not twinkle—dominates the dim surrounding constellation, Cancer. Just to the right of the brilliant planet you will see an eerie little smear of faint light. That is the Beehive.
The Beehive's 350 stars are spread over a patch of sky three times the diameter of the full moon. Photograph courtesy of NOAO/AURA/NSF.
The Beehive's individual stars lie on the tantalizing threshold of visibility. To the unaided eye, the specks of light tend to blur together into a blob. Binoculars transform the cluster into a swarm of glowing bees, and suddenly its name makes sense. Starting in late March, pointing those binoculars at Jupiter will automatically capture the Beehive in the same field of view. The cluster is easily seen even in the city. Under darker suburban skies, observers can experience the same rush that Galileo did in 1609, when he aimed his telescope at the Beehive and reported that it was "a mass of more than 40 small stars." Modern telescopes reveal about 300 more.
Galileo's discovery ended centuries of debate about the nature of this mysterious fuzz of stars. The ancient Romans called it Praesepe, Latin for "manger." Praesepe was ranked as one of the "Seven Nebulae" in Ptolemy's famous star catalog, the Almagest. The Greek astronomer Hipparchus alluded to it as "Little Cloud," and Pliny wrote about its popular use as a predictor of weather: If Praesepe was invisible in an otherwise starry sky, a thin atmospheric disturbance was blowing in, and a storm was probably on its way.
Even after Galileo, the Beehive caused confusion. In 1764 French comet hunter Charles Messier listed the Beehive as number 44 on his list of cosmic annoyances that looked like comets but were not. His list's popularity caused the cluster to be known thereafter as M44. Take your pick of what to call it—the Beehive, Praesepe, the Manger, M44, or the cluster's newest catalog listing, NGC 2632.
In the last few years, detailed observations from Europe's Hipparcos satellite, as well as ground-based telescopes, finally pinned down many key details about the Beehive. It is 577 light-years away, about 10 percent farther than previously believed, which means that the light you see today set out toward Earth when Columbus's grandparents were dating. The 350 or so members of the cluster are mostly ordinary suns like our own, with a few red giants and white dwarfs sprinkled about. The whole crew is packed into a loose ball about a dozen light-years across, about 10 times the stellar density of our immediate galactic neighborhood.
When observing faint objects, astronomers usually look off to the side. This technique, called averted vision, causes light to fall on the more sensitive periphery of the retina. Seen straight on, the Beehive cluster looks like a glowing cloud; averted vision reveals it as multiple specks of starlight.
Hipparcos also provided a major surprise: The Beehive has a long-lost twin. According to the new data, the Beehive's composition and age exactly match those of the Hyades, another stellar grouping in Taurus. The two clusters even fly through space on nearly parallel tracks. Apparently, these star communities were born together 790 million years ago, condensing from an enormous nebula as majestic as Zeus' Mount Olympus.
Both clusters are easy to see this month. The Hyades are visible as a V-shaped arrangement of stars below bright Saturn in the west after sundown. And for once you cannot miss the Beehive. Brilliant Jupiter hovers near it the entire first half of April, seemingly unmoving because Earth's curving orbit currently has us heading almost directly away from the giant planet. For a few weeks, the king of the planets will be comically but beautifully ensnared among the hovering bees.
Learn more about the Beehive at the Web site of SEDS, Students for the Exploration and Development of Space: www.seds.org/messier/m/m044.html.