Object Note
Apr 18, 2022    

While The Stargate moniker is clearly modern, this group has been known and remarked upon for centuries. Struve catalogued it and Webb noted it in his guide, thus introducing this curious group to amateur observers in the 1880's.

The binary at the center was listed by Struve as Σ 1659AB. This pair of 8th magnitude stars, HD 109556 and BD-11 3331, does appear to be a physical pair with neatly matching parallax data in Gaia EDR3 at 11.4 and 11.7mas. This pair also shares a high proper motion.

The remainder of the six stars do not appear to be physically related. The 10th magnitude red PPM 717043 that completes the inner trio is a background star, as is the fainter 9.7 magnitude BD-11 3332 of the outer triangle.

The bright HD 109545 and HD 109584 have roughly comparable parallax but radically divergent proper motions, going in opposite directions, passing in the night.

                Σ   Mv  Prlx   PMRA    PMDec
                         mas      mas/yr
    BD-11 3330  A  7.9  11.72 -146.53  18.42
    BD-11 3331  B  8.2  11.49 -144.90  21.00
    PPM 717043  C 10.1   3.36  -86.12  37.62
    BD-11 3332  D  9.8   1.62   -0.10 -15.51
    HD 109545   E  6.7   6.68   16.92 -20.80
    HD 109584   F  6.6   7.92  -19.23  22.83

While is might be tempting to consider The Stargate a cluster based on a simple look through the eyepiece it clearly is an asterism. I am surprised the various early surveyors of the sky never listed this group as a cluster.

Andrew Cooper
Apr 17, 2010    Hale Pohaku, HI (map)
46cm f/4.5 Newtonian, Deep Violet @ 175x
Seeing: 7 Transparency: 7 Moon: 0%

A great asterism, a small triangle of stars directly at the center of a larger triangle, the outer form a pretty even equilateral triangle of two 7mag stars and one 10mag star, while the inner is not quite so even, with two 8mag stars and a 12mag star

Andrew Cooper
Apr 6, 2007    Hale Pohaku, HI (map)
15cm f/5 Newtonian, Primero @ 35x
Seeing: 8 Transparency: 7 Moon: 0%

A great asterism consisting of a very small triple arranged in a isosceles triangle surrounded by a larger equilateral triangle of bright stars, each triangle is opposite of the other (rotated 180°), the inner part has two 8th magnitude stars and one 12th, the outer consists of two 6th magnitude stars and one 10th magnitude star, located 1° southwest of M104

Rev. T.W. Webb
May 19, 1885    Hardwick, Herefordshire, England (map)

(Σ 1659) De. notices that this triangularly arranged triple is within a large triangle, 7, 7.2, 9.5

― Celestial Objects for Common Telescopes, T. W. Webb, 1917

Steve Coe

1 degree SW from M 104 in Virgo; 4 stars of 7th magnitude including double star Struve 1659

― SAC Asterism Database

Drawings, descriptions, and CCD photos are copyright Andrew Cooper unless otherwise noted, no usage without permission.

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