A telescope or pair of binoculars might be nice, but you may not even need them Saturday night (March 4) to watch the half-moon approach and then dramatically snatch Aldebaran from the sky. This wonderful event, called on occultation, happens during convenient evening viewing hours across much of the U.S. and Central America. From the tippy tops of the northeastern and midwestern states, the moon will narrowly miss the star, but the two celestial orbs will still be dramatically close — reason enough to poke your head out for a look no matter where you live.
This should be one of the best Aldebaran occultations of the year, since it will disappear along the moon’s dark limb, making it relatively easy to see with the naked eye right up to the moment the moon steals the star away. An occultation occurs when the moon passes directly in front of a star or planet. The event can last more than an hour if the star passes centrally behind the moon but only seconds or minutes for observers fortunate enough to see it occur near or along the moon’s edge.
As the moon travels around its orbit, it occasionally passes in front of one of several bright stars, either Regulus in Leo, Antares in Scorpius or Aldebaran in Taurus. Aldebaran is the brightest of the bunch and exciting to watch blink out as the moon, speeding along at a kilometer a second, temporarily covers it from view. With occultations, I’m always on the edge of my seat, since it seems to take the moon forever to cover it even when the two are practically touching. As you watch, you’ll swear the star looks like it’s “inside” the moon and yet still visible. Then all at once — pfft! — it’s gone. You hate to blink!
Most stars appear as only the tiniest of points and disappear with great suddenness as soon as the moon blocks them from view, but Aldebaran is a red giant star and while it snaps away quickly enough, it doesn’t happen instantaneously as with many other stars. Instead, because of its girth (44x the sun’s diameter), the moon takes a slight fraction of a second to completely cover it. Will you notice this slight delay?
The map shows the yes/no occultation zones and the graze line, where things get really exciting. Since I live in Duluth, Minn. I’m thrilled that the line passes just 40 minutes south of me within easy driving distance. Not so thrilled that the forecast is for cloudy skies Saturday night! Along that line, observers can watch the star flash in and out of view as it disappears and reappears multiple times from behind lunar mountains and crater rims. Truly a wonderful sight for those living life on the line.
For detailed, sectional maps of the graze line along with cloud forecasts and more, check out this special Aldebaran graze website. To really drill down to a specific location on Google Maps, go to the Google Maps for Specific Elevations section on the site, click on an elevation (follow directions) and then zoom into the map as far you like.
Earlier I said that the occultation will be visible with the naked eye, but I’d still recommend binoculars or a small telescope for the best views. A little magnification enlarges the scene and gives you more of a front row seat feel.