Swing By Juno On Your Way To Comet Wirtanen

Comet 46P/Wirtanen is still a big, fuzzy ball as seen here on Dec. 8. Binoculars easily show its brighter center. You’ll need an 8-inch or larger telescope to see the short tail pointing northeast from within the coma. Michael Jäger

Many of us have been hunting up comet 46P/Wirtanen these December nights, but there’s another solar system critter near the comet you might want to check out — asteroid 3 Juno. They’re both in the same region of the sky, so after you’re finished observing 46P, you can nudge your binoculars or telescope about 10° (one fist) to the southeast to spot the asteroid.

While Wirtanen is fuzzy from all the dust and gas it’s releasing, Juno’s a point of light slowly moving among the stars of the constellation Eridanus (ear-RID-duh-nuss). At mid-month it shines at magnitude 7.8, equal to Neptune, which just had a close conjunction with Mars last week. I can see Neptune in 8×40 binoculars from a moderately light-polluted sky, so for many skywatchers, Juno will be a binocular object.

Tonight, the comet is just 10° above the asteroid Juno. Use this wide map to get oriented and the detailed map (below) to pinpoint the asteroid. Juno’s position is shown for Dec. 10. Stellarium with additions by the author
This more detailed map shows stars to magnitude 8. Juno’s position is shown every 5 nights and the comet each night. You can match up the stars 21, 22 and 23 Eri on this chart with the wide view above. Chris Marriott’s SkyMap with additions by the author

The asteroid fades slowly through December and January but stays as bright as magnitude 8.5 through mid-January, keeping within the range of 10×50 binoculars. Any telescope will show it throughout the current apparition. The best time to see Juno is from around 8 p.m. local time, when it’s well up in the southeastern sky, until 1 a.m. That’s a nice, big window. Conveniently, it makes a nifty equilateral triangle with the bright stars Rigel and Aldebaran.

These photos of Juno taken with the 100-inch Hooker telescope at Mt. Wilson Observatory show what appears to be a 60-mile-wide crater at lower left. Sallie Baliunas et al.

3 Juno is a main belt asteroid located that orbits the sun between Mars and Jupiter. Today it’s 100 million miles (160 million km) from Earth. The number “3” in front of its name tells us it was the third asteroid discovered. The lucky person to first see it was German astronomer Karl Harding on Sept. 1, 1804 back when asteroids were still called planets. With a diameter of 145 miles (233 km), Juno’s the 11th largest asteroid in the main belt. A study of reflected sunlight from its surface indicates it’s a rocky object with a composition similar to common meteorites called chondrites picked up on Earth.

Because Juno is relatively close to the Earth, it’s brighter than usual, so now is a great time to take a look. Once you find it come back and look again a few nights later to see that it’s moved, unlike the stars around it which stay put. Let us know if you find it — good luck!


4 Responses

  1. Edward M. Boll

    Still overcast for the next 3 nights at least. Possibly clearing most of the time from Thursday through Sunday. I will have to see it to believe it. And although Wirtanen is at it’s brightest next week, to me it will be best worth a view every clear night during the following week, when it will be very high. Again every night unless one is still looking at Comets 38 and 64 occasionally. If I had s big enough scope I would follow Wirtanen although less frequently till April it even May.

    1. astrobob

      Last night, Wirtanen was next to a 4.8 mag. star. The two together made the comet more obvious than previously. I looked up, and it was instantly naked eye. I estimated mag. 4.8. 64P was interesting last night. It’s very diffuse (except for the core) with a surprisingly large coma.

  2. Tom l Pettit

    Bob may I use your story called “Seeing stars the American Indian way” as a story in my daily writings on Onstellar. You will be given full credit. Thanks.

    1. astrobob

      Hi Tom,
      Thank you for writing and asking, and I appreciate the nod. I’m afraid though you can’t publish the story without payment. You can link to it if you like but not publish as it basically belongs to the Duluth News Tribune. Not sure what the cost would be.

Comments are closed.