Adhara: Brightest Star in Ultraviolet Light

This frames the region of the Milky Way in southern Canis Major and northern Puppis, rich in a variety of star clusters and some nebulosity. The field of view is 15º by 10º. At right the brightest stars are in Canis Major: yellow-white Wezen (Delta Canis Mjaoris) and blue-white Adhara (Epsilon Canis Majoris), with orange Sigma Canis Majoris between them. Above left of Wezen is the large cluster NGC 2354, and above it the smaller and brighter NGC 2362. At top left is a Messier cluster, M93, in Puppis. At far left is the bright magenta emission nebula NGC 2467. At lower left near the frame edge is the cluster NGC 2489. At bottom is the cluster NGC 2439, while the group of stars at bottom centre is the cluster Collinder 140, a distinctive object in binoculars. I call it the J Cluster as it looks like a letter J. The large diffuse faint nebulosity at top is Sharpless 2-310, though wisps of emission nebulosity extends down past the star Aludra, Eta Canis Majoris, below centre. At upper right near the orange star Omicron Canis Majoris is the faint cyan arc of the large planetary nebula Sharpless 2-308, aka the Dolphin Head Nebula, barely visible here. Left of the big Sharpless emission nebula is a small blue reflection nebula van den Burgh 98. Above the NGC 2362 cluster at the top of the frame is another small blue reflection nebula, van den Burgh 96. — A region of sky in southern Canis Major and northern Puppis. Adhara is visible in the lower right as a large blue-white star. Yellow-white Wezen is above Adhara to the left and orange Sigma Canis Majoris sits between them. (Image credit: Alan Dyer/VWPics/Universal Images Group via Getty Images)

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How to see
What is Adhara?

Adhara, also known as Epsilon Canis Majoris, is a striking star in the constellation Canis Major.

Shining as the second-brightest star in its constellation and the 22nd-brightest star in the night sky, Adhara offers a captivating glimpse into the wonders of the cosmos.

How to spot Adhara in the night sky

Adhara is located in the southern celestial hemisphere within the constellation Canis Major, famously home to Sirius, the brightest star in the night sky.

To find Adhara, first locate Sirius, then look just below to see a distinct triangle of bright stars. Adhara is visible in the lower right of this triangle. Adhara's 1.5 magnitude makes it relatively easy to spot in areas with minimal light pollution.

The best time to observe Adhara is during the late fall to early spring months in the Northern Hemisphere. In the Southern Hemisphere, it is visible high in the sky during the summer. Observers in latitudes north of 54°N may struggle to see Adhara due to its southerly position.

Despite its relative obscurity, astronomer Jim Kaler praised the sight of Adhara in the night sky.

"In fact, Adhara, a class B (B2) bright giant, is quite the magnificent star," he wrote. "Among the hotter of bright stars, Adhara shines with a surface temperature of some 21,900 degrees Kelvin [39,000 Fahrenheit or 22,000 Celsius], which gives it a sparkling bluish cast."

Location of Adhara in the night sky lying close to the horizon. — Adhara is visible in the constellation Canis Major. (Image credit: Stellarium)

What is Adhara?

Adhara is a binary star system approximately 430 light-years from Earth. The primary star, a blue-white supergiant, is the dominant component of the system, with its companion being a fainter, less massive star. The primary star's surface temperature is an intense 20,000 Kelvin, making it one of the hottest stars visible to the naked eye.

If people could see in ultraviolet light, Adhara would be the brightest star in the sky. When taking that band of light into account, the star is about 22,300 times more luminous than the sun, Kaler added.

Daisy Dobrijevic joined Space.com in February 2022, having previously worked as a staff writer for All About Space magazine. She completed an editorial internship with BBC Sky at Night Magazine and worked at the National Space Centre, communicating space science to the public.

Daisy holds a PhD in plant physiology and a Master's in Environmental Science. Based in Nottingham, U.K., she covers all things space, with a special focus on solar activity and space weather. She also has a keen interest in astrotourism and is always on the lookout for the next northern lights adventure.

She will be a guest speaker aboard HX's Solar Eclipse Expedition in August 2026 and will join Hurtigruten as an onboard astronomer for a northern lights sailing in January 2027.