Iota Cancri is a beautiful binary star in the constellation Cancer the Crab. It’s best viewed in the spring. The star doesn’t often make the headlines, but rewards those who pause to look more closely.
The brighter star, Iota Cancri A, glows with a distinct golden or yellowish-orange hue, characteristic of a G-type giant star. Beside it sits its companion, Iota Cancri B, a smaller, fainter star shining with a contrasting pale blue or blue-white light, typical of an A-type main sequence star. This striking color difference has earned Iota Cancri the popular nickname the “Spring Albireo,” drawing comparisons to the famous gold-and-blue double star Albireo visible in the summer constellation Cygnus.
With an apparent magnitude of about 4.0, the primary star (A) is technically visible to the naked eye in dark conditions, but its companion (B), shining at magnitude 6.6, requires optical aid. Thankfully, the pair is separated by a comfortable 30 arcseconds, making them relatively easy to split even at lower magnifications in small telescopes.
Observing them offers a wonderful glimpse into stellar diversity. The primary is an evolved giant star, nearing the later stages of its life, while the secondary is still burning hydrogen on the main sequence. According to Jim Kaller, if we could stand on the larger yellow star, the smaller white/blue star would appear as bright as our full moon!
The discovery of Iota Cancri as a double star around 1777 is credited to the German-Moravian astronomer Christian Mayer. He was observing from the Mannheim Observatory and systematically cataloged numerous double stars between 1776 and 1778, publishing his findings in 1779. This catalog was one of the earliest dedicated efforts to list double stars, and his observations of Iota Cancri around 1777 marked its recognition as such in astronomical records.
My Observations
| Date | March 12, 2021 |
| Time | 9:52 p.m. |
| Location | Seattle, WA |
| Magnification | 102x |
| Scope | Meade 8″ SCT |
| Eyepiece | 20mm |
| Seeing | Average |
| Transparency | Average |
This double star is absolutely stunning due to the contrast between the golden star and the light blue star. Perhaps I’m easy to please on this clear and moonless night, but I’m enjoying staring at this colorful gem, which rivals other well-known colorful doubles.
Key Stats
| Constellation | Cancer |
| Best Viewing | Spring |
| Visual Magnitude | +4.1 | +6.0 |
| Separation | 31.3″ | 5280 AU |
| Position Angle | 307° |
| Distance from Earth | 330 ly |
| Orbital Period | Unknown |
| Milky Way Location | Orion Spur |
| My Viewing Grade | B+ |
| Designations | SAO 80416, Struve STF 1268, HIP 43103, IOT CNC |
Sources and Notes
Photo of Iota Cancri by Jeffrey Fisher, http://jeffreysboldlygoingnowhere.com/. This image is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
The Garden Astronomer 