The moon’s bright and near full, but if you wait until after it sets, there’s still a sliver of dark sky before dawn. This morning a quiet arc of aurora glowed in the north while I did some comet hunting after moonset. Auroral activity has kicked up of late from the combined effects of solar outbursts called CMEs (coronal mass ejections) and coronal holes.
The aurora wasn’t the only thing setting the sky aglow. As fall approaches, so too the angle at which the ecliptic meets the eastern horizon at dawn. When that angle is steep, as it is now through early November, we get a good look at the zodiacal light. It looks like a fat finger or cone of diffuse light tilting up from the eastern horizon.
Like breadcrumbs dropped to mark a trail, comets shed dust particles each time they cycle about the sun. Asteroid collisions also contribute. The dust accumulates in the plane of the planets and glows by reflected sunlight. To see the zodiacal light while the crickets murmur at dawn is to witness the comings and goings of countless comets across generations of humanity.
With the Full Harvest Moon knocking on the door, we’re done with dark sky after tomorrow morning. Mark your calendar for September 22. Not only is that the first day of fall, but the zodiacal light returns to a dark sky and remains visible for two full weeks.
Something invisible to most of us is one its way to Earth’s skies tomorrow afternoon. That’s when the recently discovered asteroid 2014 RC rips across half the sky in a span of hours while making a very close approach to our planet. The approximately 60-foot-wide, house-sized space rock will skim the outer edge of the geosynchronous satellite belt only 25,000 miles (40,000 km) from the hairs on your head around 2:15 p.m. Eastern Daylight Time. It was discovered on September 1.
Nothing to worry about here as the asteroid will safely pass by Earth. 2014 RC will return in the future, but no threatening passes have been identified. Though most of the really bad-boy 1-km or larger Earth-approaching asteroids have been discovered, many smaller ones remain large. An estimated 1 million NEOs (Near-Earth objects) in the 100-foot (30-meter) are still out there. Surveys like those carried out with the PanSTARRS-1 telescope in Maui, Hawaii and the Catalina Sky Survey are constantly on the lookout for them. At least once a month, a new Earth-approacher is found.
Because 2014 RC will brush by Earth during daylight hours for the Western hemisphere, we’ll miss it. Observers in other parts of the southern hemisphere where it’s dark might spot it with a 6-inch or larger telescope as an 11.5 magnitude star moving as fast as a slow satellite through the field of view.
While most of us won’t see the asteroid in our own telescopes, plans are underway for radar imaging with the Goldstone dish in California. Italian astronomer Gianluca Masi will also have telescope trained on the space rock and feature it live on his Virtual Telescope Project site beginning today at 6 p.m. EDT. Take a look!