Zeta Coronae Borealis is a tight pair of equally bright stars in the Corona Borealis constellation. It’s best viewed from late spring through summer.
It seems many observers report both stars as bright white. However, some great research provided by John Nanson uncovers an intriguing historical description of the pair. According to Nanson, astronomer Admiral Smyth observed the colors of the stars as bluish-white and “smalt blue” in August 1831.
But what is “smalt blue”? Nanson reports smalt blue is a “powdered blue glass used to color vitreous materials.”
Others report seeing a tinge of green in the pair. One thing we can agree on: This is a rewarding pair regardless of the exact color!
My Observations
| Date | May 20, 2022 |
| Time | 11:00 p.m. |
| Location | Seattle, WA |
| Magnification | 169x |
| Scope | Meade 8″ SCT |
| Eyepiece | 12mm |
| Seeing | Average |
| Transparency | Above Average |
At first glance, these two stars seem plain white. However, as I let my eyes adjust and take them in, they both have a tinge of pale blue. They are of equal brightness and make a good pair in this region of the sky.
Key Stats
| Constellation | Corona Borealis |
| Best Viewing | Spring |
| Visual Magnitude | +4.9 | +6.1 |
| Absolute Visual Magnitude | +.11 |
| Distance from Earth | 520 ly |
| Separation | 6.5″ | 1030 AU |
| Orbital Period | Unknown |
| Milky Way Location | Orion Spur |
| My Viewing Grade | B |
Sources and Notes
Banner adapted from an illustration created by Pablo Budassi. The illustration is licensed under the Creative Commons Attribution-Share Alike 4.0 International license. Full details here.
1 “A Pair of Jewels in the Crown: Σ1964 and Σ1965 (Zeta (ζ) Coronae Borealis).” Star-Splitters, 30 May 2013, https://bestdoubles.wordpress.com/2011/05/15/a-pair-of-jewels-in-the-crown-%CF%831964-and-%CF%831965-zeta-%CE%B6-coronae-borealis/.
AKA: ζ Coronae Borealis, SAO 64833, STF 1965
The Garden Astronomer 