Before we embark on today’s topic, let’s update where we’re at with Nova Delphini 2013. For the past day it’s plateaued around magnitude 5.0, maybe even rising a tad to 4.9. It remains easily visible in binoculars high in the southeastern sky at nightfall.
Light from the nearly full moon now drenches the sky, making it nearly impossible to glimpse the nova with the naked eye. Dark skies return about Aug. 23. Let’s hope it hangs in there till then.
On August 8 NASA scientists used the 230-foot (70-meter) Goldstone radar antenna in Goldstone, Calif. to bounce radio waves off near-Earth asteroid 2005 WK4.
By studying the reflected radar echoes, they reconstructed a sequence of images of the giant boulder, estimated at between 660 and 980 feet (200-300 m) in diameter. In a delightful coincidence that’s about as big as the 1,000-foot Arecibo radio telescope in Puerto Rico, the largest in the world. Astronomers used this dish to observe 2005 WK4 in July 2012.
Video of 2005 WK4 on Aug. 7 by Gianluca Masi. The asteroid appears only as a point of light in even the largest optical telescopes. The radar technique not only gives precise positions of nearby asteroids but also reveals their shapes and surface features
The asteroid missed Earth by a long shot – 1.93 million miles (3.1 million km) – but the data gained by radar studies will help refine 2005 WK4’s orbit well into the future. It also transformed what had been a mere point of light into a real world, albeit a small one. The Goldstone sequence covers 6 1/2 hours during which the asteroid completed 2.4 rotations.
While you’re out gandering at the nova tonight, give a look at the big, bright moon in your binoculars. About 4-5 degrees to its left on the opposite side of the field of view are two bright stars, Alpha and Beta Capricorni in Capricornus the Sea Goat. Alpha looks like the perfect double star, where you might envision each in orbit around the other. Guess again. It’s a total fake – just a chance alignment that convincingly mimics the real thing.
Below it shines Beta. Here we have a genuine double with a 6th magnitude companion orbiting close by to the west. The moon helps us find Alpha and Beta Cap with ease, but glare could make spotting Beta’s companion a bit of a challenge at least tonight. Give it a try to see for yourself.