Iota Cancri (ι Cancri A & B)
Coordinates, Gaia DR3 distance (330 ly), 30.7″ gold-and-blue double star (G8 Iab + A3 V), and observing guide for Iota Cancri.
Provenance-Backed Scientific Measurements
Every measurement below preserves its unit, uncertainty interval, observational method, reference epoch, quality status, and primary catalog source. See Uncertainty & Provenance for how competing measurements are handled.
| Parameter | Value | Uncertainty | Method & Epoch | Quality Status | Source Archive |
|---|---|---|---|---|---|
| Apparent visual magnitude (Iota Cancri A) | 4.02 mag | ± 0.01 mag | Johnson UBV photometry (companion Iota Cancri B = 6.57 mag) | definitive | Hipparcos New Reduction Catalog |
| System distance (Gaia DR3) | 101.4 pc | ± 1.1 pc | Gaia DR3 astrometric parallax of A & B (~9.86 ± 0.11 mas / 330.7 ly) (J2016.0) | definitive | ESA Gaia Archive — Data Release 3 |
| Visual A–B angular separation | 0.512 arcmin | ± 0.002 arcmin | WDS & Gaia DR3 astrometry (30.7 arcseconds at PA 308°; ~3,100 AU projected) | definitive | ESA Gaia Archive — Data Release 3 |
| Primary effective temperature (Iota Cancri A) | 4990 K | ± 50 K | G8 II spectroscopy (companion Iota Cancri B = 8,800 ± 150 K) | definitive | SIMBAD Astronomical Database (CDS) |
J2000 Equatorial Sky Chart & Culmination Altitude
The chart below plots Iota Cancri (Spring Albireo Color Double) at RA 08h 46m 41.82s, Dec +28° 45′ 35.6″ within Cancer, alongside peak meridian transit altitudes for 40°N and 30°S observers. Use the RA/Dec Coordinate Converter to compute exact culmination altitude for your latitude.
Astrophysical Context & Structure
Iota Cancri (48 Cancri), marking the northern claw of Cancer the Crab ~8.5° north-northwest of the Beehive Cluster (Messier 44), is famously nicknamed 'the Spring Albireo' because its 30.7-arcsecond angular separation and vivid yellow-gold versus sapphire-blue color contrast closely mirror Beta Cygni (Albireo). Moreover, while Gaia astrometry has cast doubt on whether Albireo A and B are physically bound, Gaia DR3 confirms that Iota Cancri A and B share virtually identical parallaxes (9.86 milliarcseconds, or 101.4 parsecs / 331 light-years) and co-move through space separated by at least 3,100 AU.
The primary star, Iota Cancri A (magnitude 4.02), is an evolved ~3.4-solar-mass G8 II–Iab bright giant (~21 solar radii, 215 solar luminosities, 4,990 K) fusing helium in its core, while its 6.57-magnitude companion Iota Cancri B is a younger-looking 1.9-solar-mass A3 V main-sequence shell star (8,800 K) rotating rapidly inside a thin circumstellar gas envelope.
Spectroscopically, Iota Cancri A is classified as a mild Barium star (G8 II Ba0.4), enriched in slow-neutron-capture (s-process) elements like barium and strontium. Because barium stars normally acquire their s-process elements via wind mass transfer from an asymptotic-giant-branch companion that has since cooled into an unseen white dwarf, Iota Cancri A likely harbors a hidden close white-dwarf companion in addition to wide visual companion B.
Practical Visual Observing Guide
- Located 8.5° north-northwest of the Beehive Cluster (M44) along the Cancer–Lynx border.
- With a wide 30.7-arcsecond separation along position angle 308°, Iota Cancri splits cleanly in any 50–80 mm telescope at 25×–60× (or steadily mounted 15×70 binoculars), showcasing a rich dandelion-gold primary and a pastel robin's-egg blue secondary.
Catalog Cross-Identifications & Aliases
Common Aliases: ι Cancri · HD 74739 / HD 74738 · HIP 43103 · 48 Cancri
| Catalog Authority | Identifier |
|---|---|
| GAIADR3 | 704966762283019520 |
| HIP | HIP 43103 |
| HD | HD 74739 |
| SIMBAD | * iot Cnc |
| WIKIDATA | Q13066 |
Related Objects, Comparisons & Guides
Albireo (Beta Cygni Color Double Star)
Coordinates, Gaia DR3 parallaxes of Beta Cygni A & B, 34.6″ angular separation, color contrast, and observing guide for Albireo in Cygnus.
55 Cancri e (Janssen) — Ultra-Hot Super-Earth
Reference data for 55 Cancri e: 0.737-day orbit, 8.0 Earth masses, 1.88 Earth radii, magma-ocean dayside, and JWST thermal emission spectra.
Castor (Alpha Geminorum Sextuple System)
Coordinates, Hipparcos distance (50.8 ly), 5.6″ A–B binary orbit, YY Geminorum eclipsing pair, and observing guide for Castor.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Stellar Spectral Classification (OBAFGKM)
Reference guide to Morgan-Keenan (MK) stellar classification (O B A F G K M), luminosity classes (I–V, WD), color index (B-V), and the H-R diagram.
Scientific Sources & Dataset Provenance
- ESA Gaia Archive — Data Release 3 (DR3 (2022-06-13)): Gaia Collaboration, Vallenari, A., et al. 2023, A&A, 674, A1 (Gaia Data Release 3) — European Space Agency / Gaia DPAC
- Hipparcos New Reduction Catalog (2007 New Reduction): van Leeuwen, F. 2007, A&A, 474, 653 (Validation of the new Hipparcos reduction) — ESA / van Leeuwen (2007)
- SIMBAD Astronomical Database (CDS) (2026-10 release): Wenger, M., et al. 2000, A&AS, 143, 9 (The SIMBAD astronomical database) — Centre de Données astronomiques de Strasbourg