Copernicus — Star in Cancer
HIP 43587; Rho1 Cancri; 55 Cancri
About Copernicus
Description
55 Cancri (Rho1 Cancri) is a nearby binary about 41 light-years away — a G8 V primary at magnitude 5.95 with a faint M-dwarf companion 85″ away. The primary, 55 Cnc A, hosts five known planets including 55 Cnc e, a transiting super-Earth twice the mass and twice the diameter of Earth that orbits in just 17.7 hours.
Observing Tips
55 Cnc A is at the limit of comfortable naked-eye visibility from a moderately dark site — easy in binoculars. The wide M-dwarf companion B is a good test for a small telescope at moderate power. Located in the heart of Cancer, just south of the Beehive Cluster (M44).
History
Recognised as a binary by William Herschel in 1781. The first 55 Cnc planet (55 Cnc b) was announced in 1996 — the fourth exoplanet ever found around a sun-like star. By 2007 the system had four known planets, and in 2012 the inner super-Earth 55 Cnc e was confirmed by transit, making it one of the first transiting super-Earths ever measured.
Fun Facts
55 Cnc e orbits so close that its dayside temperature exceeds 2,000 °C — hot enough to vaporise rock. Spitzer infrared observations have suggested the planet may have a thick supercritical-fluid atmosphere or even oceans of molten silicate.
Observe
1Physical Properties
2Position & Identifiers
3How easy to spot?
| Equipment | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| Naked eye Naked eye | Hard+ | Hard | V. hard+ |
| 50 mm finder 50mm finder | Easy | Easy | Easy |
| 150 mm telescope 150mm scope | Easy | Easy | Easy |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
4Visibility
Set a location in User Settings to see visibility data.
5Survey Image
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Explore
6
Size Comparison
7
Compare Stars
8
Spectral Classification
9
Hertzsprung-Russell Diagram
10
Stellar Lifecycle
11
Blackbody Spectrum
12
Stellar Absorption Spectrum
Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.
13
Stellar Fusion
14
Exoplanets
5 known planets
View in 3D
| Planet | Radius | Mass | Period | Distance |
|---|---|---|---|---|
| 55 Cnc e | 1.88R⊕ | 8.0M⊕ | 0.7d | 41ly |
| 55 Cnc b | 13.90R⊕ | 0.83M♃ | 14.7d | 41ly |
| 55 Cnc c | 8.51R⊕ | 54.5M⊕ | 44.4d | 41ly |
| 55 Cnc f | 7.59R⊕ | 44.8M⊕ | 260.6d | 41ly |
| 55 Cnc d | 13.00R⊕ | 3.88M♃ | 13.1yr | 41ly |
Habitable Zone
Size & Mass Comparison
About exoplanets — how we find them and which host stars you can observe
Discover
15Stellar Notes
16
Light Travel Time Machine
17
Relativistic Travel
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
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