Double Star of the Month Archive 2026
In this series of short articles, a double star in both the northern and southern hemispheres will be highlighted for observation with small telescopes, with new objects being selected for each month.
January 2026 - Double Star of the Month
The Hyades moving group contains stars which are not immediately proximate to the open cluster on the sky. The most famous is perhaps Capella, a bright spectroscopic binary with a 104 day period which is orbited by a binary pair of red dwarfs. Another member is ENG 22 (05 41 20.33 +53 28 52.7) which can be found 2.5 degrees WSW of delta Aurigae (V = 3.7).
It was catalogued by Rudolf Engelmann but recent measures by the Gaia satellite have revealed the parallax and proper motion of both components. The pair consists of stars of V magnitudes 6.0 and 8.9 which lie at a mean distance of 40.0 light-years and which are moving across the sky at 0".5 per year. The separation and position angle have remained fixed at 98" and 72 degrees so this is probably a binary system. The primary is a K dwarf and the companion has spectral type M0.
Adhara = epsilon CMa (06 58 37.55 -28 58 19.5), at V = 1.5, is the second brightest star in the constellation, but 4 million years ago, it was the brightest star in the sky reaching magnitude -4.
In the nineteenth century a visual companion was seen at the Cape Observatory, some six magnitudes fainter and 7".5 distant in position angle 167 degrees. Ernst Hartung noted that the the pair can be seen in 75-mm aperture, and that the primary is brilliant white whilst the companion is deep yellow.
The brightness of the primary is probably the reason why the error in the parallax found by Hipparcos is significantly larger than usual. Gaia has no results for this star but it is possible that the brightest stars in the sky will be investigated towards the end of the project. The satellite was switched off on March 27, 2025 and work on the Gaia DR4 catalogue is now in progress and the results are expected towards the end of next year.
Bob Argyle - Double Star Section Director
If you'd like to try out the Clear Skies Observing Guides (CSOG), you can download observing guide for the current Double Stars of the Month without the need to register. CSOG are not associated with the Webb Deep-Sky Society but the work of Victor van Wulfen.
