Sagitta

Sagitta


Transit Date of principal star:
17 July


Sagitta, "The Arrow", while small and insignificant, is a constellation known to the Greeks. Some references believe that Sagittarius, the Archer, shot the arrow (apparently without a known target); others talk about Cupid, and Heracles, and Apollo. The point is, there isn't any established myth associated with Sagitta.

The constellation has a number of interesting items, including several multiple binary systems and a Messier object.

The Bayer stars range from 3.5 to 6.5. Note that the brightest star here is gamma Sagittae.


Double stars:

Zeta Sge (Struve 2585) is a close binary with 22.78 year orbit; it's also a multiple system:
AB: 5.5, 6.5; PA 180, 0.2"
C: 9; PA 311, 8.0"
D: 11; PA 247, 75".
Theta Sge (Struve 2637) is also a multiple system:
AB: 6.6, 8.9; PA 332, separation 11.5"
C: 7, PA 223, separation 84".


Variable stars:

S Sagittae is a fairly bright cepheid, ranging from 5.5 to 6.2 every 8.38 days.

To locate S Sge, drop three degrees south of gamma Sge. The bright star here is 11 Sge. S Sge is in the same field, just to the west-southwest.
U Sagittae is a well-known Algol-type eclipsing variable, suitable or small telescope or binoculars.

Use the nearby star just to the NE (Struve 2504, visual magnitude 7.9) as a comparison; U Sge is slightly brighter than this star at its regular brightness, then dips far below (to about 9.2) every 3d9h8m5s as the larger companion completely eclipses the primary. This lasts for about 1h40m, then the star rapidly regains its brightest magnitude.

U Sagittae is five degrees west of alpha Sge, and 1.75 degrees to the north. It forms an equilateral triangle with two brighter stars, 1 Vulpeculae and 4 Vulpeculae. (Note: on Tirion's Sky Atlas, U Sge appears to have the label "OU" due to the size of the star itself.)


Deep Sky Objects:

M71 (NGC 6838) is classified as a globular cluster, but it looks much more like an open cluster. It's found just between delta and gamma Sagittae and slightly south.


For a more detailed appreciation of Sagitta visit the Binocular Section.


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