Definition
Phi Ursae Majoris (φ UMa) is the Bayer designation for a star—or, in some catalogues, a multiple‑star system—located within the northern constellation Ursa Major.
Overview
The designation φ UMa is used in astronomical catalogues to identify a celestial object that is visible to the naked eye under dark‑sky conditions, with an apparent visual magnitude close to 5. The star lies in the western part of Ursa Major, relatively near the asterism formed by the “handle” of the Great Bear. In many modern star catalogues the entry for φ UMa is treated as a visual double, consisting of two components that can be resolved with modest telescopic equipment.
Etymology / Origin
The name follows the Bayer system introduced by Johann Bayer in his 1603 star atlas Uranometria. Bayer assigned Greek letters to stars roughly in order of decreasing brightness within each constellation; φ (phi) is the twenty‑second letter of the Greek alphabet. “Ursa Major” is Latin for “Great Bear”, the traditional name of the constellation.
Characteristics
- Spectral type: Several astronomical databases list the primary component as a G‑type star (commonly G8 III or G8 IV), indicating a yellow‑hued giant or subgiant.
- Apparent magnitude: Approximately 5.0–5.2, making it faintly visible to the unaided eye.
- Distance: Parallax measurements from the Hipparcos mission place the system at roughly 150–170 light‑years from the Sun, though exact values differ among catalogues.
- Multiplicity: The system is recorded as a visual binary with a companion of roughly 9th‑mag visual magnitude, separated by a few arcseconds; the pair shares a common proper motion, suggesting a gravitational bond.
- Radial velocity and proper motion: The star exhibits a modest radial velocity toward the Sun (a few km s⁻¹) and a proper motion of several tens of milliarcseconds per year.
Note: While the above properties are widely cited in astronomical reference works (e.g., the Bright Star Catalogue, the Hipparcos Catalogue, and the SIMBAD database), small variations exist between sources, and some details—such as the exact spectral subclass and the physical nature of the companion—remain subject to refinement by ongoing observations.
Related Topics
- Bayer designation – The systematic naming of stars using Greek letters and constellation names.
- Ursa Major – The constellation containing φ UMa, notable for the asterism known as the Big Dipper.
- Binary and multiple star systems – Stellar systems where two or more stars are gravitationally bound.
- Stellar classification – The spectral categorisation of stars based on temperature and luminosity.
- Hipparcos and Gaia missions – Space‑based astrometric surveys that provide precise measurements of stellar positions, parallaxes, and proper motions.