The winter constellation of Taurus has a good collection of double stars. Chi Tauri, also known as 59 Tau or Struve 528, is a pretty white-blue (purple) pairing added to the mix.
Since the primary star (Chi Tauri A) and the secondary star (Chi Tauri B) have decent spacing between them at 19 arcseconds, most observers shouldn’t have trouble splitting the two. What can make observing this pair tough is the dim magnitude of +8.5 registered for Chi Tauri B. Still, most smaller telescopes should be able to see both.
Where things get a little more interesting is with the secondary star Chi Tauri B. On paper, this dim star is a yellow G2 V class star, and apparently, it’s also a binary with another F-type star. One would think this quaint secondary would appear yellowish, but it doesn’t at all. Most observers see blue! In my case, I see a deep purple! Chi Tauri reminds us of the mystery of optics and what our own eyes see at times.
Historically speaking, William Herschel first recorded this pair on October 30, 1779.
My Observations
| Date | January 23, 2023 |
| Time | 8:00 p.m. |
| Location | Seattle, WA |
| Magnification | 169x |
| Scope | Meade 8″ SCT |
| Eyepiece | 12mm |
| Seeing | Average |
| Transparency | Below Average |
The bright primary star is a brilliant white-blue color; it breaks through the high atmospheric haze well. That star looks as expected, but this secondary dim star is truly interesting. Here’s why, when I first came upon this pair with my 24mm eyepiece, I thought the secondary was red. However, as I “zoomed” in using the 12mm eyepiece, the color looked dark blue/purple! Wow.
On top of this, I understand from research that this secondary is actually a G-type yellow star!
Key Stats
| Constellation | Taurus |
| Best Viewing | Winter |
| Visual Magnitude | +5.4, +8.5 |
| Absolute Visual Magnitude | +.63 |
| Distance from Earth | 291 ly |
| Separation | 19.4″ |
| Position Angle | 25° |
| Milky Way Location | Orion Spur |
| My Viewing Grade | B+ |
| Designations | χ Tauri, STF 528, SAO 76573, HIP 20430 |
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“Chi Tauri.” Wikipedia, Wikimedia Foundation, 26 Mar. 2022, en.wikipedia.org/wiki/Chi_Tauri. Accessed 29 Mar. 2023.
Sketch by Wayne McGraw
The Garden Astronomer 