Planetary system · 5 known planets · Cancer

55 Cancri

55 Cnc A

Its star: above the horizon after darkHighest after dark 05:17 · east · 44°

Join the waitlistSkyMate is coming to iPhone

Where is 55 Cancri?

Times for LondonChange city

Look east, about 44° up at 05:17 in Cancer. It rises at 00:00 and climbs through the night.

Rises: 00:00
Highest: 08:54
Sets: 17:52
Best after dark: 05:17 · 44°

Can I see 55 Cancri?

No. The planets of 55 Cancri can’t be seen with the eye, binoculars or any amateur telescope: they are lost in their star’s light. What you can do is point toward the star.

From London tonight, the star 55 Cancri is above the horizon after dark. It’s highest just before dawn, around 05:17, in the east at 44°.

Why is 55 Cancri interesting?

55 Cancri has 5 known planets, discovered between 1996 and 2007 by the radial velocity, primary transit and radial velocity methods.

What can you see?

Eyes

Direction only

Around magnitude 6: at the limit of naked-eye visibility under dark skies.

Binoculars

Easy to see as a star north of the Beehive Cluster.

Telescope

A yellow-orange star. The planets themselves can’t be seen with any backyard telescope.

What you’re likely to see, not what a space telescope photographs.

About

55 Cancri is a pair of stars about 41 light-years away in Cancer: a yellow-orange star slightly cooler than the Sun, with a distant red dwarf companion. The brighter star has five known planets.

The innermost, 55 Cancri e (also named Janssen), is a scorching super-Earth that orbits in less than 18 hours. Its surface may be covered in molten rock, and observations suggest it may have an atmosphere.

The outermost known planet is a Jupiter-like giant on a long orbit, making this one of the richest planetary systems known.

The host star is just visible to the naked eye under dark skies.

55 Cancri e is nearly twice Earth’s width and about eight times its mass, and it always keeps the same side facing its star. Its dayside is thought to be hotter than 2,000 °C.

The 55 Cancri system

Known planets of 55 Cancri (catalog values from exoplanet.eu)
Planet	Mass	Radius	Orbit	From star	Found	Method
55 Cnc Ae	8.58 M⊕	1.86 R⊕	17.7 h	0.016 AU	2004	Radial Velocity, Primary Transit
55 Cnc Ab	0.87 M♃	—	14.7 days	0.118 AU	1996	Radial Velocity
55 Cnc Ac	0.18 M♃	—	44.4 days	0.247 AU	2002	Radial Velocity
55 Cnc Af	0.15 M♃	—	260.6 days	0.802 AU	2007	Radial Velocity
55 Cnc Ad	3.81 M⊕	—	13.1 years	5.6 AU	2002	Radial Velocity

M⊕ / R⊕ = Earth masses / radii; M♃ / R♃ = Jupiter. Masses from radial velocity are often minimum masses. Data: The Extrasolar Planets Encyclopaedia, exoplanet.eu (CC BY 4.0).

Questions

Can I see 55 Cancri e?

No. You can see its host star under dark skies, but not the planet.

Is 55 Cancri e made of diamond?

That idea was suggested in 2012, but later studies do not support it. It is better described as a lava world.

Another planetary systemTau Ceti Another planetary systemEpsilon Eridani 9° awayBeehive Cluster 14° awayTegmine GuideStargazing for beginners ToolMoon phase & visibility tool

Sources: The Extrasolar Planets Encyclopaedia (CC BY 4.0); star chart: Wikidata (CC0). Positions computed for your place and time with astronomy-engine. Data & Licences