Sarin, known as Delta Herculis (δ Herculis), is a variable and bright double star in the constellation Hercules, which is best viewed in summer. The star is the third brightest in Hercules and lies around 75 light-years away from us.
According to Jim Kaler, Sarin is a multiple-star system. In the center, one will see the double stars Delta A and B. The primary, known as Delta A, is a glowing bright white at magnitude +3.1, while the 8th magnitude Delta B is relatively close at 12.7 arcseconds. Then, there are several other outlier stars nearby associated with Delta A.
As Kaler points out, these stars are only optically related as their motion doesn’t match Delta A.1 If you want to see the locations of these outliers, I suggest viewing the really good Delta Herculis post on the Star Splitters website.
Historically speaking, the astronomer William Herschel first saw this star as a double on August 9, 1779.2
My Observations
| Date | July 29, 2022 |
| Time | 11:02 p.m. |
| Location | Seattle, WA |
| Magnification | 169x |
| Scope | Meade 8″ SCT |
| Eyepiece | 12mm |
| Seeing | Average |
| Transparency | Average |
This multiple-star system offers more than the average double star in the sky. For one, there is a tight optical double right in the middle of my field. The primary white star glows brightly, with its slightly hazy light reaching out toward the bluish secondary. Then, several companion blue stars circle around the center. I know good sky conditions will bring out more stars in the field. But from my location and average sky conditions on the warm summer night, I’m settling for a quad of blue stars around Delta Her A.
Key Stats
| Constellation | Hercules |
| Best Viewing | Summer |
| Visual Magnitude | +3.1 | +8.3 |
| Absolute Visual Magnitude | +1.32 |
| Distance from Earth | 75 ly |
| Separation | 12.″ | 648 AU |
| Position Angle | 288° |
| Orbital Period | Unknown |
| Milky Way Location | Orion Spur |
| My Viewing Grade | B |
| Designations | Struve (Σ 3127), HIP 84379, SAO: 84951, 65 Her |
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 Kaler, J. (n.d.). Delta Herculis. Retrieved April 18, 2023, from http://stars.astro.illinois.edu/sow/deltaher.html
2 The Herschel 500 double star list. (n.d.). Retrieved April 18, 2023, from https://www.handprint.com/ASTRO/Herschel500.html
The Garden Astronomer 