A glimpse of a large asteroid comes to delight sky-watchers this month, silently sailing its way through a cosmic bull’s horns and past a famous supernova remnant.
In the next few weeks, the asteroid Herculina, the 532nd asteroid to be discovered, will glow in the sky at a magnitude of brightness of about 10. That should make it easy to spot with small backyard telescopes, even through the glare from cities.
This 140-mile-wide (230-kilometer-wide) space rock is in the top 20 of the largest asteroids known to reside within the main belt of asteroids that lies between Mars and Jupiter. It has a surface that appears brighter than that of Earth’s moon, but because of its distance—normally some some 260 million miles (400 million kilometers) away from Earth—it lies beyond the reach of most backyard astronomers.
Now, however, thanks to its elliptical orbit, Herculina will come as close as 160 million miles (250 million kilometers) away from our planet, offering us a golden opportunity to observe an otherwise tough stargazing target.
To add Herculina to your astronomical bucket list, use the sky chart above to locate its approximate position in the constellation Taurus, the Bull.
Start at the bright orange beacon of Aldebaran, the eye and the tip of the distinctive V-shaped face of Taurus, which is now riding high in the southwestern sky in the early evening.
Through the first half of February, the asteroid is whizzing by Zeta Tauri, the magnitude-3 star that marks the tip of the southern horn of the bull.
On the nights of February 5, 6, and 7, Herculina will be its closest to Zeta Tauri, making the star a wonderful guidepost for locating it.
Because many of the stars in your field of view through your telescope’s eyepiece will probably look the same, the best way to identify an asteroid is by its telltale motion. But since asteroids this far away from Earth don’t appear to move across the sky over the course of a few minutes or even hours, identifying their subtle presence will take a little patience. Sketch the position of about a dozen stars you see through your telescope’s eyepiece. Then a couple of nights later, observe the same starfield and do the same thing. The one “star” that has moved is Herculina.
Catching the Crab
Then around Valentine’s Day next week, look for Herculina to pass by one of the most famous stargazing targets for backyard scopes—the supernova remnant known as the Crab Nebula, or Messier 1.
At the closest approach on the 14th, Herculina and the Crab will appear only 30 arc-minutes apart—a width equal to the disk of the full moon in the sky.
Instruments as small as binoculars will pick up the 8th-magnitude fuzzy oval glow of the supernova remnant only about a degree above Zeta Tauri. It will appear in the same field of view under low magnification in your telescope.
It’s amazing to think that the Crab Nebula is a cloud of debris 6,500 light-years away. Measuring nearly 11 light-years across and still expanding, the nebula is all that is left of a giant star that appeared to explode in Earth’s skies back in the year A.D. 1054.
The blast was so bright and powerful that Chinese astronomers at the time made note of this “guest” star, which appeared as bright as Venus for 23 days.
For more celestial sights, check out our weekly sky-watching column.