Late summer is globular cluster season. Almost all of the globular clusters in the Messier Catalogue are visible at this time of year. Well, if the weather cooperates, that is. Which it didn’t out at the Denver Astronomical Society’s dark site last night.
Globulars are collections of tens of thousands, hundreds of thousands, or even millions of stars, all crammed into a spherical space anywhere between 30 and 100 light years across. They are among the oldest structures in our galaxy, about 12-13 billion years old, almost as old as the universe itself.
Actually, they aren’t in our galaxy. They orbit our galaxy out beyond its edges, stuck in the dark matter halo that extends out from the galaxy. There are about 150 of them orbiting the Milky Way; meanwhile, Andromeda has about 500. They do not contain any gas or nebula to create new stars. The stars that are present are almost all just about as old as the glob itself. We’re able to determine this because the stars in globs have such low metal content. Stars like our sun have higher metal content, because they are formed from the gaseous remnants of a previous supernova, which creates these metals. Older stars, with low metallicity (not low Metallica), are formed from the original hydrogen and helium created by the Big Bang.
The formation of globs is not very well understood. One of the more interesting things I recently learned about them is why they don’t collapse under their own gravity – why the stars, which are so tightly packed in, don’t just get sucked in towards the center. This is because the stars orbit the common center of mass in a completely random way. If they orbited in the same direction, like planets around a star, or like moons around a planet, they would eventually flatten into a disk – like moons and planets do in their orbits in our solar system. The fact that they orbit randomly, like electrons around a nucleus, creates a counter-pressure to the gravity that wants to suck them in.
Last night the weather forecast was for clear skies out at the dark site, 60 miles east of town. Well, not exactly clear skies. More like clearing skies. The forecast was that a front would move through, and that partially cloudy skies just after sunset would become clearer around 9pm or so, with clear skies predicted for around 11 or 12. That didn’t happen. Gee, I’m shocked, shocked to find that the forecast was inaccurate.
Okay, it kinda happened. The “partially cloudy skies” after sunset were mostly cloudy, with a couple/three sucker holes for binocular observing with my 12×60 Oberwerks in different parts of the sky. I found that I could just squeeze Arcturus, setting in the west, and another brighter star in Bootes, 3rd magnitude Muphrid, below and to its right, in the same field of view of the binoculars. Checking later on Stellarium, this means that I have a field of view of just a shade over 5 degrees.
Continuing to sucker around, I was able to pretty easily pick up M4, right next to Antares, and as that sucker hole drifted along, I could see M22, one of my favorites. As one formed to the east, the Double Cluster and surrounding Milky Way was visible in Cassiopeia. We got a quick look at Saturn in yet another hole, as I fired up the scope. The seeing conditions were not great with weather fronts moving through. Even using my 12.5mm ortho at just 123x, the image was starting to break down.
Unfortunately, the SLT mount isn’t really designed for sucker hole observing. Yes, you can do it, but it’s not like just swinging a dob around on its mount and just checking out whatever part of the sky you want to see. The SLT does not have unlockable clutches, so you have to turn on the motor and use the handset to slowly slew from one area of the sky to another. I did this later in the night to get some telescopic views of the Pleiades (M45) and the Triangulum Galaxy (M33). The first were glorious; the latter, not so much. Its surface brightness is just far too low – a dim patch, barely visible in either the ST-80 or the Mak.
This makes me want to look into getting Orion’s StarSeeker IV mount. This is essentially a Celestron SE mount, because almost all astrogear is built in about four factories in China. The SS IV is Synta-made, in the same factory where they make the SEs. However, the SS IV has unlockable clutches and optical encoders so you don’t lose your alignment if you decide to move the scope manually.
Getting the SS IV would solve three “problems” I have with my SLT mount. First off is that the plastic spreaders have broken off yet again. JB Welding them back on didn’t work – or I just have no talent for using it – so I’m concerned that someone looking through the scope, or even I, might kick out one of the legs accidentally, and whoops! Down goes Frazier! Down goes Frazier! Down goes Frazier!
Mind you, the SS IV is $400. For that much, I could get a brand new 127SLT in its entirety – which would, of course, include a brand new mount. On the other hand, broken spreaders or not, the SLT still does work, and work fine. While any new mount would take care of the crashing scope “problem”, the SS IV would take care of two more – second, by unlocking the clutches, it would allow for much easier sucker hole astronomy on nights like last night; and third, and most important to me, it would carry my Mak/’frac combo without the clutch slipping.
The SLT mount is only rated for the 8 lbs that the Mak OTA weighs. Strapping my ST-80 onto the Mak , the weight goes up to 12 lbs. When I try to view anything higher than about 50-55 degrees in elevation while using the Frankenscope, the clutch slips and I have to catch the end of the scope to keep it from crashing into the mount. The SS IV has a payload capacity of 13 lbs. – just like the SE mount. So this slippage problem would forever be solved, plus I’d have a much more capable, sturdier, yet still easily portable, mount to put the Frankenscope on. Something to think about spending even more of my Jeopardy money on.
By 9pm, most of the clouds had cleared off, and the sky was pretty clear all around. I had planned to do a glorious globular tour, starting right after the end of twilight, about 8pm. I wanted to do a compare and contrast between them all – which ones were just kinda visible; which ones were better than visible, and which ones were pretty darned good! I typically write up an observing list on the back of an envelope, then flip it over to keep going. But last night’s list was so long, there are so many globs, that they’d never all fit on an envelope.
28 of the 110 Messier objects are globulars. Last night, or more to the point, generally around this time of year, about 25 of them were easily visible within a few hours, between around 8pm and 11 pm or so. Here’s my observing list, compiled from Stellarium:
In the hour or so before the winds came sweeping down the plain, after taking a look at some old friends down Sagittarius way, I was able to observe some of the first group of these: Messiers 19, 62, 69, 70, 54, 55, 28, and 22. M22 is one of my favorites, and it was wonderful, as always. Almost all of the rest were just dim spherical splotches, one no different from the next. In terms of my compare and contrast of globs, I wasn’t surprised by this. Most items in a 5-inch scope, even from a dark site, just aren’t all that spectacular. (Man, I can’t wait to get that C9.25 already!)
However, I was really surprised at one of the globs I was able to see: M55. I wasn’t expecting too much from it, as it had specs that were similar to other Messier objects in the list – mid-7th magnitude, about half the size of the moon, more or less. But it was actually quite a nice globular; I could resolve the edges into individual stars – as opposed to it looking like an unresolved mist, which all but the biggest and brightest globs look like. Checking my master list of Messiers I’ve seen, it wasn’t listed. Interesting that I had somehow missed it!
I was also surprised at one that wasn’t a Messier object at all: NGC 6723. Not that it was great, or outstanding. No, it was just another gray fuzzball. But it was just another gray fuzzball that was pretty much right next to another couple of gray fuzzballs that are Messier objects, M69 and M70. Messier was not only a careful and dedicated observer, but he was also a professional observer – he had one job! How could he miss this one? I didn’t find out “why” until I got home and rechecked Stellarium.
Unfortunately, it was only clear for just about that hour or so. Just after 10, the clouds moved in again. This time, they came with high winds – at least 20 miles per hour, sustained, with a drop in temperature. The front was moving through. The other few people out at the dark site packed up and left. I decided to stick it out, for awhile at least, because the forecast was that it would get a lot clearer after the front moved through.
It did clear up by 11; but the winds stayed. It was impossible to keep observing through the scope as it jittered violently with each sustained gust. Although it was beautifully dark and clear, the vibrations were just too much to look at anything.
After packing up, I had a final look around with the Oberwerks. I caught M11 easily, took a look at M13, and scoured rising Auriga for M36, 37, and 38, but couldn’t really see much definitively, as it was just above the horizon. I then gaped for awhile at the Double Cluster and the surrounding area, now high in the sky. I finally ended off by really drinking in Andromeda (M31) and the Pleiades (M45) – both of which are made for looking at through binoculars. Or an ST-80. Either one. So, while it was a less than stellar night (ahem) for observing with the scopes, it was pretty nice to observe with the binoculars.
I’ll talk more about Messier in my next blog post, so stay tuned!