Thursday, 17 September 2009

Observing session 16 September 2009

Another clear night, we're doing fairly well this past month or so (in the past month, we have had 20 - yes TWENTY! - clear or partially clear nights. Can't use all of them, unfortunately, but it's nice to see), so I lugged the scope out onto the patio for a, hopefully lengthy as I have no work on at the moment, observing session.

There was a nice sunset:


Cool: 11C, 75% humidity (no dew, thankfully) and a very slight breeze, which picked up now and again and died down at intervals. No Moon. Transparency was not too good at first, quite obvious from the higher-than-usual extent of light domes from nearby towns, picking up at around 0030 BST to 0200 BST, and there were isolated drifting clouds although they weren't enough to interfere with observing. The naked eye limiting magnitude was not as good as usual, around 6.0 to 6.2.

Again I spent a little too much time hunting for elusive stuff, mainly faintish galaxies that I should not have bothered with, given the less-than-great transparency. However, I am pleased with what I did observe, and got some good sketches too.

Instrument: 12 inch f/5 Dobsonian.

I have popped some sketches into this post, but they are rough as they are the original sketches and not redrawn ones.

First up was NGC 40, a planetary nebula in Cepheus. Bit of a rough sketch, though - my writing is terrible and it's not scanned properly! The nebula was bright and obvious, looking like a fat star at low power, and obviously nebulous at higher powers. It's round with a bright middle, appearing fatter when looked at with averted vision. Averted vision also hints at a darker area round the bright middle portion. OIII does not enhance the view or provide more detail.

I also found NGC 7662, the Blue Snowball, in Andromeda, easily enough this time. Heaven knows why I failed to find it the other evening, probably a combination of factors, not least the dew making life awkward. NGC 7662 is strikingly sky blue, and round with slightly fluffy-looking edges. Hint of darker centre. OIII makes little difference to the view, UHC even less so.

I had intended to make the pn blue in Photoshop, as it appeared in the scope, but having scanned it in greyscale this obviously wasn't going to work! The pic hasn't scanned very well, also I think I need to draw the eyepiece representation circle a bit darker in future.

I also spent quite a lot of time on M33, the big galaxy in Triangulum. Ok, it's a Messier lollipop, but I wasn't looking at the galaxy as a whole, I was looking for HII regions within the galaxy. Using a chart from the net I identified NGC 595 and NGC 604. I thought I saw more, but a larger scope and darker, more transparent skies would be a help. NGC 604 is easy to find, a triangle of stars pointing straight at it helps in locating it, it looked elongated, east to west, and showed a bit of brightening within. NGC 595 was much smaller, a roundish knot of light. It is always interesting to see 'objects within objects' particularly within external galaxies (M31 also contains 'objects within objects, as do the Magellanic Clouds, although these, sadly, are not visible from Europe or the United States).

I attempted the Pegasus 1 galaxy cluster, which at mag 11.1 should be accessible to the 12 inch, but there was nothing doing on this front, due mainly to the fairly murky sky. The same went for the Perseus Cluster, with ranges of magnitudes between 11.6 and 12.5. I'll have another go at these, on a more transparent night sometime this autumn and, in the case of Perseus, when it rises a bit higher. By the time Pegasus was higher the galaxies were behind the garden shed and the 12 inch is not exactly portable so I didn't bother to try again.

The last object - or objects - was Stephan's Quintet (Hickson 92) again. The transparency had improved by this time and the part of the sky where this is located was high. The Quintet was easy to find, located at the end of a chain of stars just SW of the bright galaxy NGC 7331, although not so easy to see. I sketched them, although I couldn't finish the sketch due to the fact the transparency gave out again and the galaxies vanished like smoke. Btw, what looks like a galaxy to the bottom of NGC 7319 isn't, it's a smudge on the paper I forgot to rub out and which I failed to see in Photoshop.

The last object of the night was NGC 7000, the North America Nebula in Cygnus. This large nebula is naked eye in the right conditions. I could see it without the aid of scope or binoculars. OIII made it more obvious but UHC was even better, making it very obvious, and I could easily see the 'Gulf of Mexico' dark area.

Called it a night at just after 0210 as the transparency was giving out again and the clouds, formerly the odd one or two, were increasing.