Struve 1108: A Double of Yellow and Blue with Caldwell 39 Nearby

Struve 1108 is a double star in the constellation Gemini, best viewed on winter nights.

The brightest star of the pair is +6.6 magnitude, so urban astronomers will be best off with at least a small scope to see this double. The primary star is a yellow star classified as a spectral type of G5.

The pair lie 11.7 arcseconds away from each other, so they are fairly close in the eyepiece. Out there at 440 light years away from us, the stars are 1590 astronomical units apart. According to Bob Argyle, there “has been little motion since the pair was found by F. G. W. Struve.”¹

My Observations

Tonight is chilly and high-altitude clouds are seemingly appearing out of nowhere. Still, I push on, jumping from double-star target to target as long as the sky allows. There is not much to report about Struve 1108, other than it’s a fairly close, yet nice to look at, double. The primary brighter star appears a reddish-yellow to me, while the secondary fainter star (around 8) appears a faint white with perhaps a touch of blue.

Key Stats

Constellation	Gemini
Best Viewing	Winter
Visual Magnitude	+6.6, +8.3
Separation	11.7″ | 1590 AU
Position Angle	359°
Spectral Class	Primary=G5
Absolute Visual Magnitude	+3.15
Distance from Earth	440 ly
Milky Way Location	Orion Spur
My Viewing Grade	B
Designations	STF 1108, HIP 36691, BD +23 1744

Sources and Notes

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.

¹ Argyle, Bob. “February 2023 – Double Star of the Month.” Webb Deep-Sky Society: Double Star of the Month: STF1108, https://www.webbdeepsky.com/double-stars/object?object=STF1108.

Sketch by Wayne McGraw