Most nights, I race through my variable star observations, trying to log as many as I can get as fast as I can go, before the weather changes, I run out of steam or the Sun comes up. I hop from field to field; completely ignoring celestial wonders just a few degrees away. When the longer, clear, dry nights of autumn finally come, I am tempted to take a few extra minutes along the way to take in some sights and try new challenges.
Lets say tonight is one of those glorious clear, moonless, autumn nights. You’ve decided to stop and smell the roses along the way, but you’d still like to make some variable star estimates. Or maybe a couple friends or family have stopped by for a late dinner, and now they want to look through the telescope. You need a plan.
Obviously, we’ll start in the west and north with targets that will begin to fade into the haze of the horizon if we don’t get them right away. Since it is still experiencing a record minimum, in magnitude and duration, I think we should be sure to observe R CrB first. This star could be considered a deep sky wonder itself. Usually visible in binoculars as an unassuming sixth magnitude star inside the ‘Northern Crown’, R CrB undergoes sudden, random fading episodes, sometimes to 14th magnitude. As of this writing, it is hovering just above 15th magnitude, where it has remained for longer than ever before in recorded history. In the same low power telescopic field is the semiregular variable TT CrB, ranging from 10.9- 12.1, just north of R CrB. If you have a telescope large enough to see R CrB around 14.8, you may want to continue on from TT CrB to the bright 7th magnitude star to the NW, GCS 2039 0642. Just about 10.5 minutes north of that star is a faint, round 14th magnitude galaxy, NGC 6001. I’d put identifying this in the ‘challenge’ category. To me it looks like a slightly fuzzy star, but hey, we’re just getting started.
Before you leave CrB be sure to at least check in your finder to be sure the recurrent nova T CrB hasn’t erupted. If it has, you’ll see a bright star forming a triangle with epsilon CrB and delta CrB. Stop everything at that point and send out an alert. Forget the faint fuzzies!
Much more impressive in a telescope is M5 in Serpentis. This is about as low as we want to go, and this is a better summer target, but the irregular variable Z Ser is only 38 arc minutes away, and this star is almost totally ignored by observers. AAVSO has very little data on it. The GCVS lists a range of 9.4-10.9, and a period of approximately 88 days, so it should be interesting and easy to follow. Why don’t you adopt this star into your program, and pick it up again in spring when it comes out of conjunction. It will give you an excuse to observe M5 on a regular basis without diminishing your serious variable stars observer status.
From there we swing north to the great globular M13 in Hercules. Even I’m not so jaded that I don’t like to take a few minutes to take in the finest globular cluster visible in the northern sky. But let’s not get carried away. Waiting for us about one and a half degrees NW is the fine Mira variable W Her. W Her varies from 8th to 14th magnitude, so it’s usually visible in an 8-inch scope, and always visible in a 10 or 12-inch.
About halfway to our next destination is an anonymous little star cluster in Lyra, easily visible in your finder scope. Just to the east of the two brightest stars in the cluster is CY Lyrae, a fun little U Gem star that is fairly active, outbursting into the 13th magnitude range every couple weeks or so. Even if it’s not visible tonight, you won’t have wasted your time visiting here. This one is off the well-beaten path of deep sky wonders. It’s a pretty well kept secret amongst variable star folk, and we aim to keep it that way, so shhhh…don’t tell anyone.
If you have company at the observatory, M57 is one of the stops you’ll make anyway, so here is your chance to quickly locate and show them a real crowd pleaser, the Ring Nebula in Lyra. Located in the same low power view as the ghostly ring of this planetary nebula is another Mira variable RX Lyr. If you make it a point to observe this variable this month you’ll be able to make a positive observation as it is just beginning to fade from maximum, around 11.2, on its way to the inner sanctum. It spends a lot of time fainter than 14th magnitude, so I always consider it a treat to make a positive observation of a variable so close to M57.
Our next stop is in Draco, the Cat’s Eye Nebula. Located about midway between zeta and delta Draconis, this is another bright planetary nebula on the usual star party agenda. Yes, it’s nice. Take a few moments to soak it in and explain to your guests how planetary nebulae are the remnants of old evolved stars, and then swing about one degree SE and you can show them two such stars in one field, W and X Draconis, one of my favorite “twofers” in the sky. X Dra is located next to an unmistakable triangle of field stars and should just be visible in a 10 or 12-inch around 14th magnitude if you hurry. Like RX Lyr, it spends a good deal of time fainter than 14th magnitude and has a period of 257 days. W Dra ranges from 9-15th magnitude, so it is almost always visible in medium sized scopes. These two are only 14 arc seconds apart, so they are in the same medium to high power field.
From there you can glide into the Milky Way, starting your tour with everyone’s favorite double star, Alberio, beta Cygni. Beta 1 Cyg, the orangish K star of the pair is even suspected of being variable, although I doubt you could do much to prove or disprove this visually. But it is one of those fun facts I like to throw in just to discourage guests from ever coming to a star party at my observatory again! From there it is a relatively easy jump to M56, a globular with a bright core, about 3.75 degrees NW of Alberio, and then almost due east 4.7 degrees is one of the prettiest star fields containing a variable star in the sky. The variable is EM Cyg, a Z Cam star that varies from 11.9 to 14.4, so it is always visible in medium sized telescopes. After you’ve made your estimate you can encourage visitors to slowly slew around the area getting lost in the diamond-clustered field against an ink-black backdrop.
Continuing along the body of “The Swan” to the NE you’ll come to chi Cygni. With a dramatic range from naked eye visibility (magnitude 3 or 4) to 14th magnitude, this is one of the AAVSO ‘legacy Miras’; with data going back a hundred years or more. If tat isn’t enough to impress visitors you can track down any number of star clusters, planetary nebulae or diffuse nebulae within a couple degrees of this variable. In fact the area east of chi is a large bright diffuse nebula with the sexy name GN 19.50.2. If that doesn’t impress your guests, slew NW to the “Blinking Nebula” and demonstrate averted vision with the ‘now you see it, now you don’t’ planetary nebulae NGC 6826.
You’ll have to go south again to visit the Dumbbell Nebula, M27. Then you can take a break from the telescope to observe one of the stars in the 10-Star Training Tutorial, eta Aquilae. This is a bright Cepheid observable with binoculars or the naked eye. The observant visitors will want to know what that bright star is in the south, so be prepared to blow your dark adaptation with some glaring views of Jupiter and the Galilean satellites.
By now M31 should be high enough to see with the naked eye from a dark site. You can show visitors where you’re pointing the telescope next while you explain that the Andromeda Galaxy is the furthest thing you can see with the naked eye, some 2.5 million light years away. After you get an eyeful of Andromeda you can swing over to another AAVSO favorite, RX And. This active Z Cam star ranges from 10.3 to 14.0 and it is always doing something. It’s either trying to hide around 14th magnitude, in outburst at 10 or 11 or stuck in a standstill somewhere in-between on any given night.
A little further east and you’ll come to U And, a nice well behaved Mira that varies from 9.9 to 14.4 in 346 days. It’s in a very nice field of stars with a bright triangle of 8th, 9th and 10th magnitude stars to the NE of the variable.
This is a good point to stop. If you really want to squeeze in one more deep sky treat you can slew south to M33 before capping the telescope and calling it a night. Depending on how late it is in the evening or the season, hints of the winter sights to come may be just visible in the east as Orion begins to rise into view. In the next issue, we’ll talk about deep sky treats and variables worth braving the arctic air of a northern winter.