After a week of clear afternoons followed just like clockwork by cloudy skies at dusk, I was thrilled to death to get a clear night, even though the moon was almost full. You can’t be picky when you live on the north Oregon coast, where there are as many clouds as there are seagulls.
Sagitta has been on my mind for the last month or so (yes, I know, strange mind — but when it comes to double stars, it goes to its destination like an arrow flies to a target), so I thought I would take a look around tonight, starting at the western end. The tail of the arrow which outlines this constellation is held down by Alpha (α) and Beta (β), and just south of them are our first two stars, Epsilon and H N 84. The first was discovered by William Herschel on August 19th, 1780, and the second on August 22nd, 1792. Both of these can easily be seen in the same field of view in a 60mm scope.
Epsilon (ε) Sagittae (H VI 26) HIP: 96516 SAO: 105061
RA: 19h 37.3m Dec: +16° 28′
Magnitudes AB: 5.8, 8.4 AC: 5.8, 12.6 AD: 5.8, 9.6
Separation AB: 87.7″ AC: 101.2″ AD: 162.8″
Position Angles AB: 82° (WDS 2012) AC: 278° (WDS 2001) AD: 348° (WDS 1992)
Distance: 473 Light Years
Spectral Classification: “A” is G9, “B” is B9, “D” is K0
H N 84 HIP: 96688 SAO: 105104
RA: 19h 39.4m Dec: +16° 34′
Magnitudes: 6.4, 9.5
Position Angle: 301° (WDS 2012)
Distance: 2297 Light Years
Spectral Classification: K4, B3
At 40x in my 60mm, Epsilon’s (ε) primary looked to me to be yellow with a very slight tinge of red and the secondary was white. I worked hard at trying to get a glimpse of “C”, but the bright moon, which was about forty degrees away, just made the sky too bright to detect it. ** Update 11/17/2014: It appears that the magnitude for the “D” component is incorrect since there is no 9.6 magnitude star at the position given for it. In fact, there’s not even a star at that location that is anywhere near bright enough to be “D”. More to come shortly. **
The colors of H N 84 are very close to those of Epsilon (ε), but the primary is slightly darker and has a bit more red in it.
It’s easy to mix these two pairs of stars up on first sight. You may need to use their position angles to make the distinction when you first come across them, especially if you only see one of them in your eyepiece, which is what happened to me. In a refractor, you’ll see that Epsilon’s (ε) secondary lies at a position angle of eighty-two degrees, which puts it almost due east of the primary, whereas in the case of H N 84, the secondary lies at 299 degrees, putting it on the opposite side of the primary. In other words, these two stars are almost mirror images of each other. I came across Epsilon (ε) first, thinking it was H N 84, and kept muttering to myself that the secondary was in the wrong place, until the real H N 84 drifted into view in the right side of my eyepiece — and then the light came on! In the bathroom window opposite my second story observing deck! Geez, I hate it when that happens.
Zeta (ζ) (Σ 2585) (H II 30 — AB-C only) HIP: 97496 SAO: 105298
RA: 19h 49.0m Dec: +19° 09′
Magnitudes AB: 5.6, 6.0 AB-C: 5.0, 9.0 AB-D: 5.0, 11.0
Separation AB: 0.18″ AB-C: 8.0″ AB-D: 76″
Pos. Angles AB:148° (WDS 2007) AB-C: 311° (WDS 2012) AB-D:246° (WDS 2005)
Distance: 327 Light Years
Spectral Classification: “A” is A1, “C” is F5
Status: “A” is a suspected spectroscopic binary; “AB-C” is physically related; “AB-D” is optical
OK, light’s off, so now it’s time to move slightly northeast to Delta (δ) and then a bit north in order to reach Zeta (ζ), which provides a nice contrast with Epsilon (ε) and H N 84. At 8.0″ apart, you have to look just a bit closer in a 60mm scope to see the AB-C pair. I could just separate them at 40x, but increasing the magnification to 53x proved to be enough to put some dark sky between them. I had to bring in the big gun, the 152mm refractor, to make the eleventh magnitude “D” component visible at 87x. I never did see it in the 60mm, but under a dark sky, with it’s distance of 76″ from the primary, it should be possible to get a glimpse of it. I increased the magnification on the 152mm scope to 122x and was rewarded with a very nice view of all three components.
If you look at the data for Zeta (ζ) above, you’ll see that “A” and “B” are .18″ of an arc second apart — which means we don’t have a snowball’s chance in a hot oven of separating them. If you’ve ever wondered what a label such as “AB-C” means, then now you know! Normally combining the two stars into one by dropping the dash indicates a spectroscopic pair – which these two are not, but they’re pretty darn close.
Time to take a break and put the light screen up. It looks like the friendly folks next door have decided to leave that minus 15th magnitude bathroom light on all night.
Next stop: Theta!
(WDS info updated 9/8/2013)