ConstellationsTonight

Corona Borealis, the Northern Crown, in July

Kite-shaped Bootes with star Arcturus at its 'tail' and C-shaped northern crown nearby.
View at EarthSky Conmmunity Photos. | Dr Ski in Valencia, Philippines, caught this photo of Arcturus and its constellation Boötes, next to the Northern Crown, in 2019. Thanks, Dr Ski!

Look for Corona Borealis between 2 bright stars

In the evening in July, look for the constellation Corona Borealis, also known as the Northern Crown. You’ll need a dark sky to see it. But, if you have one, the constellation is easy and distinctive. It makes the shape of the letter C. In the middle of the C is a white jewel of a star. This star, the brightest light in the Northern Crown, is called Alphecca or Gemma.

To see this famous C-shaped assemblage of stars from the Northern Hemisphere, you’ll be looking high overhead during the evening hours in July. From the Southern Hemisphere, the constellation is low in the northern sky.

The Crown is located more or less along a line between two bright stars. The first is the orange star Arcturus in the constellation Boötes the Herdsman, shown in the photo at top. The second is beautiful, blue-white Vega in the constellation Lyra the Harp.

Arcturus has already passed its highest point in the evening at this time of year and is slowly descending to the west. Vega is still high in the east on July evenings. With dark skies you will notice the orange color of Arcturus and Vega’s bright blue-white tinge.

Corona Borealis can be found between these two stars, though closer to Vega. Remember, a dark sky is best for seeing this faint semicircle of stars.

Star chart with Arcturus and Vega labeled and small northern crown constellation between them.
Look for Corona Borealis between the stars Vega and Arcturus.

Gem of the Northern Crown

The brightest star in Corona Borealis is Gemma at magnitude 2.22. The meaning of this Latin star name should be obvious. This star is the gem of the Northern Crown.

But, as is the case with many stars, this star has more than one name. It’s also called Alphecca. This second name is from an Arabic phrase meaning the bright one of the dish. So you can see that, throughout history, stargazers have identified Corona Borealis with a common shape: a bowl, a disk, a crown.

By the way, Gemma, aka Alphecca, is an eclipsing binary system. It consists of a smaller sunlike star that passes in front of a brighter star every 17.4 days, as seen from our earthly vantage point.

Read more about Gemma, aka Alphecca, in the Northern Crown

Six bright stars in bowl shape against a starry sky, Alphecca noticeably brighter.
Corona Borealis, the Northern Crown, with its brightest star Alphecca or Gemma. Image via Fred Espenak/ AstroPixels. Used with permission.

Other bright stars in Corona Borealis

The second brightest star, Beta Coronae Borealis, has the name of Nusakan. Nusakan shines at magnitude 3.66. Nukasan and Alphecca lies a little less than three degrees apart. Nukasan lies 114 light-years away, and Alphecca lies a bit closer at 75 light-years away. A dim galaxy of magnitude 15 lies just 19 arcminutes away from Nukasan. You can only see it with very large telescopes.

The other stars that make up the curved shape of Corona Borealis are all 3rd and 4th magnitude. Theta lies on the other side of Nukasan and Gamma and Delta lie on the other side of Alphecca. Gamma is a double star, but the two are very close and require high magnification and steady skies to see.

Man on rooftop of city with Corona Borealis and Hercules outlined in sky.
View at EarthSky Community Photos. | Prateek Pandey in Bhopal, India, captured this photo of Corona Borealis, Hercules and neighbors on April 3, 2021. He wrote: “Hercules and the neighboring constellations in the North-eastern sky.” Thank you, Prateek!

Bottom line: On these July evenings, look for Corona Borealis’ graceful semicircle of stars between two bright stars: Arcturus and Vega.

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Posted 
July 3, 2021
 in 
Constellations

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