In the autumn constellation Vulpecula is the popular Brocchi’s Cluster, nicknamed the Coat Hanger. It consists of approximately 10 stars arranged in a distinctive shape that resembles an upside-down coat hanger or a shepherd’s crook. You’ll find several double stars in this region, including the quaint Struve 2540 among a pretty background of faint stars.
Stuve 2540 is a triple star, though most backyard urban astronomers will only see the brighter pair referred to as Struve 2540 A and B. The two stars are a pretty tight pair, only separated by 5.4 arcseconds. The primary star shines at a magnitude of +7.5, while the secondary star has a fainter magnitude of +9.3. Both are white stars of spectral type A3.
As John Nanson points out on Star Splitters, this tight double stands out nicely among a field of 10th and 11th-magnitude stars.
My Observations
| Date | October 15, 2023 |
| Time | 9:22 p.m. |
| Location | Seattle, WA |
| Magnification | 169x |
| Scope | Meade 8″ SCT |
| Eyepiece | 12mm |
| Seeing | Average |
| Transparency | Average |
As soon as I saw this pair in my field of view, I was impressed by how well I could distinguish them using my 12mm eyepiece. The primary star had a yellow-white tint to it, while the secondary was fainter and had a white color. While this pair may not stand out at first glance, I have slowly started to notice more faint stars appearing in the field as I sketch. It’s a shame that my view is hindered by light pollution, as I’m certain that this double star would be even more stunning to observe under clear skies.
Key Stats
| Constellation | Vulpecula |
| Best Viewing | Autumn |
| Visual Magnitude | +7.5 | +9.3 |
| Separation | 5.4″ |
| Position Angle (between AB & C) | 147° |
| Spectral Class | A=A3, B=A3 |
| Absolute Visual Magnitude | +1.61 |
| Distance from Earth | 498 ly |
| Milky Way Location | Orion Spur |
| My Viewing Grade | B- |
| Designations | SAO 87342, HIP 96171, STF 2540 |
Sources and Notes
The banner illustration was created by the European Southern Observatory (ESO) and is under the Creative Commons Attribution 4.0 International License. Per ESO agreement: Here is the original image on the ESO website.
Sketch by Wayne McGraw
The Garden Astronomer 