39 Tauri
A nearby G-type binary star in Taurus.
39 Tauri is a binary star system located in the northern constellation Taurus. Its apparent visual magnitude of 5.90 means it can be faintly seen from suburban skies under the Bortle scale. Based on parallax measurements from the Hipparcos spacecraft, the system lies about 55 light-years from the Sun. The two stars were resolved using speckle interferometry, although the secondary star has often eluded detection in other observations.
The primary star is classified as G5 V, a G-type main-sequence star; the secondary’s type is not known. Stellar models suggest the primary is similar to the Sun, with 110% of its mass, 96% of its radius, and nearly the same luminosity. Its metallicity—the abundance of elements heavier than hydrogen and helium—is also Sun-like. Estimated to be about one billion years old, it rotates with a period of 9.12 days. Hipparcos data show a mild variability of 0.06 magnitude in brightness.
The system’s space velocity components are –25.0 (U), –14.0 (V), and –6.0 (W) km/s. Its surface activity and motion are consistent with membership in the IC 2391 moving group. It follows an orbit through the Milky Way with an eccentricity of 0.06, bringing it as close as 7.34 kiloparsecs to the Galactic Center and as far as 8.21 kiloparsecs. Its orbital inclination keeps it within 10 parsecs of the galactic plane.
- Apparent magnitude
- 5.90
- Distance
- ~55 light-years
- Spectral type (primary)
- G5 V
- Mass (primary)
- 110% of the Sun
- Radius (primary)
- 96% of the Sun
- Rotation period (primary)
- 9.12 days
- Age
- ~1 billion years
Lore & Background
39 Tauri is a binary star system located about 55 light-years from the Sun, based on a Hipparcos parallax of 0.0594728″. The primary component is a G-type main-sequence star with a stellar classification of G5 V, similar to the Sun but slightly more massive (110% of the Sun's mass) and slightly smaller (96% of the Sun's radius). Its luminosity is nearly identical to the Sun's, and its metallicity is also similar. The star is relatively young, with an estimated age of one billion years, and rotates with a period of 9.12 days. Hipparcos data indicate a mild variability with an amplitude of 0.06 magnitude.
The secondary star has been detected via speckle interferometry, but its spectral type remains unknown, and many attempts to resolve it have failed. The system's space velocity components are –25.0 (U), –14.0 (V), –6.0 (W) km/s, and its surface activity and kinematics are consistent with membership in the IC 2391 moving group. 39 Tauri follows an orbit through the Milky Way with an eccentricity of 0.06, ranging from 7.34 kpc to 8.21 kpc from the Galactic Center, and stays within 10 pc of the galactic plane.
Reader's Guide
39 Tauri is notable as a nearby solar analog whose primary star closely resembles the Sun in mass, radius, luminosity, and metallicity, but at a younger age of about one billion years. Its rotation period of 9.12 days and mild variability provide a comparative benchmark for stellar evolution studies. The binary nature of the system, confirmed by speckle interferometry yet often elusive to observation, adds a layer of complexity to its characterization. The secondary component's unknown type leaves open questions about the system's formation and dynamical history. Membership in the IC 2391 moving group ties 39 Tauri to a kinematic association of young stars, offering context for its age and motion. The star's orbit within the galaxy, with low eccentricity and a narrow range of distances from the Galactic Center, suggests a relatively quiet dynamical history. For observers, its magnitude of 5.90 places it at the threshold of naked-eye visibility under suburban skies, making it a modest but accessible target for amateur telescopes equipped for binary star work. The Hipparcos data revealing a 0.06-magnitude variation underscore its subtle photometric behavior, which may be linked to rotation or activity.
Did You Know?
- 39 Tauri has an apparent visual magnitude of 5.90, faintly visible from suburban skies.
- The primary star has 110% of the Sun's mass but only 96% of its radius.
- The system is a member of the IC 2391 moving group.
Gallery
Frequently Asked Questions
What is 39 Tauri?
39 Tauri is a binary star system sitting in the northern constellation Taurus, roughly 55 light-years from the Sun. It is a modest, nearby pair whose primary closely resembles our own Sun.
Can you see 39 Tauri with the naked eye?
Its apparent visual magnitude of 5.90 places it right at the edge of unaided visibility, so it can be glimpsed from suburban skies under reasonably dark conditions. Heavily light-polluted urban locations would make it effectively invisible.
What is the primary star in 39 Tauri like?
The primary is a G5 V main-sequence star with a mass about 110% of the Sun and a radius around 96% solar. It completes one rotation roughly every 9.12 days, making it a close analog to our own star.
How was 39 Tauri's binary nature confirmed?
Speckle interferometry was used to split the two stars apart, overcoming the smearing caused by Earth's atmosphere. The secondary has proven stubbornly difficult to detect in other observing campaigns, so it does not always appear in follow-up measurements.
Do we know the spectral type of 39 Tauri's secondary?
No; the companion's classification remains unknown because it has so often evaded detection. What is established is that the primary is a Sun-like G-type dwarf, and the pair as a whole is a relatively quiet, nearby binary in Taurus.
More in Binary and Multiple Stars, Part 4 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced