53 Eridani
Binary star in Eridanus with a named primary component.
53 Eridani, also known as l Eridani, is a binary star system in the constellation Eridanus. Its combined brightness, as seen from Earth, is magnitude 3.87. Based on data from the Hipparcos satellite, the system lies roughly 110 light-years (33.7 parsecs) away. The two stars are labeled 53 Eridani A (which carries the official name Sceptrum) and 53 Eridani B.
The system’s Flamsteed number is 53 Eridani, while its Bayer designation is l Eridani. The A and B component labels follow the Washington Multiplicity Catalog’s convention for multiple-star systems, later adopted by the International Astronomical Union (IAU). The name Sceptrum comes from the obsolete constellation Sceptrum Brandenburgicum, created by Gottfried Kirch to honor the Prussian province of Brandenburg. Though later used by Johann Elert Bode, the constellation eventually fell out of use. In 2016, the IAU’s Working Group on Star Names (WGSN) began standardizing star names, assigning them to individual stars rather than whole systems. On 30 June 2017, the WGSN approved Sceptrum for 53 Eridani A, and it is now listed among official IAU star names.
53 Eridani is a visual binary, with its stars’ orbits determined from their motion. The primary, 53 Eridani A, is an evolved red giant of spectral type K1III—nearly ten times the Sun’s diameter and slightly more massive. The secondary, 53 Eridani B, has an apparent magnitude of 6.95; its spectral type is unknown. The two stars orbit each other every 77 years on a highly eccentric path (eccentricity 0.666). The total mass of the system is 2.49 times that of the Sun.
- Flamsteed designation
- 53 Eridani
- Bayer designation
- l Eridani
- Combined apparent magnitude
- 3.87
- Distance
- about 110 light-years (33.7 parsecs)
- Primary spectral type
- K1III
- Orbital period
- 77 years
- Orbital eccentricity
- 0.666
- Total system mass
- 2.49 M☉
Lore & Background
53 Eridani bore the traditional Latin name Sceptrum ('scepter'), as it was one of the brighter stars designated 'p Sceptri (Brandenburgici)' in the obsolete constellation of Sceptrum Brandenburgicum. That constellation was coined by Gottfried Kirch to honor the Brandenburg province of Prussia, and although later used in atlases by Johann Elert Bode, it fell out of use. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars; the WGSN decided to attribute proper names to individual stars rather than entire multiple systems. It approved the name Sceptrum for the component 53 Eridani A on 30 June 2017, and it is now included in the List of IAU-approved Star Names.
The system is a visual binary, with the orbit of the two stars calculated from their orbital motions. The primary, 53 Eridani A, is an evolved red giant of spectral type K1III, almost ten times as wide as the Sun and slightly more massive. The secondary, 53 Eridani B, has an apparent magnitude of 6.95, but its spectral type is unknown. The two have an orbital period of 77 years and a quite eccentric orbit at 0.666; the total mass of the system is 2.49 M☉.
Reader's Guide
53 Eridani is notable as a binary system whose primary component carries the historical name Sceptrum, linking it to the defunct constellation Sceptrum Brandenburgicum. This constellation, created by Gottfried Kirch to honor the Brandenburg province of Prussia, was later used by Johann Elert Bode but eventually fell out of use. The IAU's Working Group on Star Names formally recognized the name Sceptrum for 53 Eridani A in 2017, preserving a piece of astronomical history. The system itself is a visual binary with a 77-year orbital period and a high eccentricity of 0.666, indicating a markedly elliptical orbit. The primary is an evolved red giant (K1III) nearly ten times the Sun's diameter and slightly more massive, while the secondary's spectral type remains unknown. The total system mass of 2.49 solar masses provides a constraint for stellar evolution models of binary pairs. The Hipparcos parallax distance of about 110 light-years places it within a well-studied region of the sky, making it a useful object for understanding binary star dynamics and the history of constellation nomenclature.
Did You Know?
- 53 Eridani has a combined apparent magnitude of 3.87.
- The primary star, 53 Eridani A, is officially named Sceptrum.
- The system's orbital period is 77 years with an eccentricity of 0.666.
More in Binary and Multiple Stars, Part 2 1-24
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