To Delta Geminorum by way of Jupiter and Pluto

Jupiter is so close to the double star Delta Geminorum, it’s not easy to separate the two at a glance. The two will be within a degree of each other for the next week. The map shows the sky around 10 p.m. local time facing east. Stellarium

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.

Jupiter and moons and the double star Wasat (Delta Gem) through a 10-inch scope on Dec. 10, 2013. The two were only a quarter degree apart. Stellarium / Bob King

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!

Clyde Tombaugh discovered Pluto in Jan.-Feb. 1930 when it was just as close to Wasat as Jupiter is now. Stellarium

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!

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About astrobob

My name is Bob King and I work at the Duluth News Tribune in Duluth, Minn. as a photographer and photo editor. I'm also an amateur astronomer and have been keen on the sky since age 11. My modest credentials include membership in the American Association of Variable Star Observers (AAVSO) where I'm a regular contributor, International Meteorite Collectors Assn. and Arrowhead Astronomical Society. I also teach community education astronomy classes at our local planetarium.

5 thoughts on “To Delta Geminorum by way of Jupiter and Pluto

  1. April 27, 1990, my 1 year old son had ear surgery at the University of Minnesota Hospital. I returned to the university that night to hear Clyde Tombaugh talk. Even slumped over, he walked up to the platform and said that he was a plutocrat. Today, I found out about my shoulder injury. I tore some muscles in the shoulder. It will take 4-6 weeks for complete recovery. I am thankful that it was my left one. If it were my right, I probably would be unable to work.

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