The other night I looked up at the constellation Gemini near Jupiter and noticed a star missing. Where the heck was Delta Geminorum? Finally, I found it sitting so close to Jupiter it was almost lost in the planet’s glare. A quick look through the telescope showed the pair separated by less than a quarter degree.
Jupiter presented his usual striped equatorial cloud belts and a nice spread of moons, and Delta, also known by its Arabia name “Wasat”, looked like a single, ordinary star directly south of the planet. While interesting to see a planet and star so close, the pair was certainly not extraordinary.
But if you up the magnification to 150x or higher, you’d discover that Delta’s accompanied by an 8th magnitude companion star snuggled to its southwest. The two stars are close by naked eye standards – just 5.8 arc seconds or 1/300 the width of a full moon – but easily cleave with a 6-inch telescope in good seeing.
Jupiter and Delta are now so close you might have trouble separating them with your naked eye the next few nights. This is exactly what makes this a great time to pursue this interesting double star in your telescope. Just point it at Jupiter and you’re there. The two will slowly separate in the coming nights, but will stay within a degree of each other through the 20th.
Wasat lies 59 light years from Earth and its companion, a K-class orange dwarf a little smaller than the sun, is 9.3 billion miles or over 100 times farther from the primary star than the Earth is from the sun. This great distance means a long, long time for it to complete an orbit – 1,200 years!
Wasat or Delta Geminorum has another claim to fame. It was here that the dwarf planet Pluto was discovered by American astronomer Clyde Tombaugh in January 1930. Tombaugh took exposures of the sky near Delta on January 23 and 29, 1930. On Feb. 15 when he examined the images, he detected a shift in the position of a 15th magnitude speck (the future Pluto) compared to photos made on Jan. 21. Lowell Observatory in Flagstaff, Arizona, where he worked, announced the discovery to the world on March 13, 1930.
Wasat – ordinary star indeed!