Struve 764: Two White-Gray Pinpoints in Auriga

Struve 764 is a double star in the Auriga constellation, best viewed on winter nights.

The pair of stars that make up STF 764 are both off-white in color and easily separated in the sky with a telescope. The primary star is registered as a blue-white subgiant with a spectral type of B8IV. It takes on a whiter “cleaner” hue, while the fainter secondary star is grayer with perhaps a touch of green. The system lies 607 light years away, and the primary star is slightly more than three times the size of our sun.

Historically speaking, astronomer William Herschel first recorded this pair on November 13, 1790.

My Observations

Even though the seeing conditions are not excellent, I wanted to get some time under the stars since it has been many weeks since I’ve seen a clear sky. Unfortunately, bands of high clouds wash past Auriga, but my telescope and I can reach and pick out some doubles.

The primary (drawn as the left star on my sketch) appears a brilliant off-white. Maybe one could say it has a touch of blue. Meanwhile, the secondary star is a fainter gray or even a touch of green mixed. Overall, this is a nice pair, even though the colors don’t allure the eye.

Key Stats

Constellation	Auriga
Best Viewing	Winter
Visual Magnitude	+6.4 | +7.1
Separation	25.8″
Position Angle	15°
Spectral Class	A=B8IV
Absolute Visual Magnitude	+.03
Distance from Earth	610 ly
Milky Way Location	Orion Spur
My Viewing Grade	B
Designations	HR 1945, STF 764, SAO 77383

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.

Sketch by Wayne McGraw