Watch as the moon eclipses the star Antares
As soon as it gets dark this evening, take a close look at the moon, big and bright in the southeast. Just to its left will be orange-red Antares. This is one of the two brightest red-supergiant stars in the sky, but it will be so close to the dazzling moon that you may have to look carefully. Binoculars will help.
Keep watch, and you will notice something. The moon is creeping toward it, closer and closer. Soon you will definitely need binoculars. Seen from Greater Boston, the moon skims barely lower right of the fire-colored star between 11 and 11:30 p.m. When they are closest, not even binoculars may resolve them; you may need a telescope.
In fact, this is a case where the fine clockwork of the cosmos depends on where you are standing. The moon will pass across the star, suddenly blacking it out of sight, for people southwest of a line that runs from south of Brattleboro through Worcester, Attleboro, and East Falmouth to Nantucket.
Telescope users in that region will see what's called a lunar occultation of the star. To occult means to hide. The moon literally eclipses the star.
Most interesting of all will be events within a mile or two of that diagonal line itself. Telescope users stationed there will see a grazing occultation, as the mountains and valleys near the moon's north pole skim sideways across the star, perhaps making it pop in and out of view several times.
Accurate timings of these events, made by many small-telescope users spaced just a few hundred feet apart, used to provide the most accurate mapping of lunar hills and valleys. For decades, amateur astronomers have organized grazing occultation expeditions to do this, and they still are. The volunteer outfit coordinating such efforts, the International Occultation Timing Association based in Maryland, plans at least one expedition for tonight, since clear weather is forecast.
But sophisticated lunar mapping satellites are now orbiting the moon, and the heyday of the eyeball-and-stopwatch way of doing it is clearly passing.
Technology is overtaking many other areas that amateur astronomers once ruled. Most new comets are now discovered by spacecraft or robotic sky-patrol cameras, not by backyard comet hunters sweeping the sky over the neighbor's rooftop every clear night.
For more than a century, amateurs were almost the only people tracking most of the sky's variable stars. These are stars that change brightness, for a variety of interesting reasons, on time scales of minutes to months. But now, every faint star in the sky will soon have its brightness measured to high precision automatically every night by wide-field cameras that never sleep. The American Association of Variable Star Observers, based in Cambridge since 1911, has diligently compiled 16.4 million star-brightness measurements made by backyard amateurs during the last century. Its future looks to be in compiling the output of machines.
On the other hand, technology keeps opening up opportunities for amateur science. Digital video cameras, combined with intelligent frame-stacking software, allow anyone with a large backyard scope to take sharper pictures of the planets than professionals on mountaintops could do a generation ago. If no space probe happens to be at the planet, this is the cutting edge for seeing what's happening there.
And those variable stars? When one of them starts doing something really interesting, a worldwide network of amateurs with precise imaging chips can be mobilized to track it continuously with more than 10 times the precision of the old eyeball brightness judgments. The big sky-survey observatories of the future, which will track massive numbers of faint events across the heavens, are planning from the outset to harness these volunteer networks to do followup.
So even if events like tonight's are no longer cutting-edge science, energetic hobbyists are finding new ways to be more than just passive spectators to the cosmos.
Alan M. MacRobert is a senior editor of Sky & Telescope magazine in Cambridge. His Star Watch column appears the first Saturday of every month. 