The Owl and the Surfboard

Last night we were lucky enough to have some clear skies in the early part of the evening and, although there was a nearly first quarter moon, I thought it was worth trying to carry on with some observations of objects in the constellation of Ursa Major. I was again using my 4 inch Celestron NexStar SLT which is relatively quick to get set up. My target was M97, the Owl Nebula, but I knew that it was possible to get another object in the field of view and this was M108, the Surfboard galaxy (a name I hadn't heard before until I looked it up). I started observing about 9.30pm with my Nikon D90 at prime focus and I was lucky to get both objects in the field of view first time. I was again using 30s ISO3200 frames and I was keen this time to monitor the sharpness of the images and to adjust the focussing from time to time if it looked like the stars were going out of focus. So there was a lot of standing around outside (until an hour later) gawping intermittently at the sky. I was fortunate because I did see a couple of sporadic meteors. One was slow and short in the direction of Leo and but the other was much more spectacular, heading east along the Hercules/Draco border. This latter one was bright but I only caught the last fraction of it and it was big enough to break up into two separate bits.

 

Here is my final image which resulted from 42 frames (21 minutes) stacked in DeepSkyStacker. M108 (NGC3556) is the 10.0 magnitude galaxy in the upper part of the frame. Below and slightly to the right is M97 (NGC3587) a magnitude 9.9 bluish planetary nebula that gets its owl name from what look like to dark circles of eyes on the disc. If you click on the image to get a better view you can just make out the central star which is a white dwarf in the making. The binned (x2) image has been processed in Photoshop and the colours enhanced for these two objects.

All text and images © Duncan Hale-Sutton 2021

Noctilucent Clouds - 22nd June 2020

Here is another picture from last year when we had a display of noctilucent clouds.

 

 

These clouds are unusual in that they only appear in the mid-summer months and are formed at very high altitudes (typically 80 to 85km). They are made up of ice crystals that are lit by the sun which at this time of year is not far below the northern horizon. This picture was taken on the 22nd June 2020 just after midnight. I used a Nikon D90 with a 5s exposure at f/5.3 (ISO1600). The focal length was 80mm.

I wrote an article for the Kielder Observatory Newsletter in 2015 about NLC's and I reproduce it here:-

"During the summer months when the sky isn’t dark enough for deep sky observing you might be tempted to put up your astronomical feet and turn your attention to other pursuits. However, there are plenty of projects you can still get involved in and one of these is observing Noctilucent Clouds (NLC’s).

Literally meaning “night shining clouds”, these wispy formations start appearing in the summer months from about mid-May to mid-August and can be seen above the northern horizon from most parts of the UK. They tend to appear about an hour and half to two hours after sunset (or before sunrise) and look like bands or whirls of silvery blue coloured clouds. The British Astronomical Association gives a guide to observing and recording these phenomena and classifies the different types of cloud that you can see into four categories: -

1.       Veil (a simple structureless sheet)

2.       Bands (lines or streaks)

3.       Waves or Billows (fine herring-bone structure like the sand ripples on a beach at low tide)

4.       Whirls (largescale looped or twisted structures).

So how do these clouds come about? The first point to make is that they are formed at very high altitudes of 80 to 85km and appear to shine at night because they are lit by the sun which during the summer lies not far below the horizon at UK latitudes.  At this point in the upper Mesosphere the temperature is -180C and, by mechanisms that are yet not fully understood, the clouds form when water vapour freezes around tiny dust particles. So where does the water vapour and the dust particles come from? Interestingly, this is the altitude at which some meteors entering our atmosphere burn up through the intense heat of friction with the air. It has been suggested that this may be a source of the fine particles of dust. But what about the water vapour? Here some of our bovine friends may be helping as it suggested that methane may be reaching this height where, by some chemistry involving free radicals, its hydrogen is being converted into water.

So why are NLC’s of interest to scientists and why are amateurs needed to observe them? Firstly, NLC’s are observed to be a recent phenomenon. The first reports of their observation came in 1885. This is two years after the massive eruption of Krakatoa when large amounts of ash, dust and gas were ejected into the upper atmosphere. Secondly, they are being observed more frequently and at increasing lower earth latitudes. The accepted view is that NLC’s can be seen from latitudes of 50 to 65 degrees (north or south; they are seen in the southern hemisphere in summer too) but more recently they have been seen as far south as 40 degrees. So this is where amateurs can play a part. In 2007 NASA launched the AIM satellite to observe these clouds but observations from amateurs is encouraged to supplement our understanding of their range and frequency.  What’s more they may be an indicator of climate change, perhaps because, as the earth warms up more methane is released from frozen arctic bogs and this is contributing to the overall methane content of our air.

In any case, it all makes it a good reason to stay up late on summer evenings and look out for these enigmatic clouds."

All text and images © Duncan Hale-Sutton 2021

Comet Neowise - 15th July 2020

I thought I would share some of the pictures that I have taken over last year. In 2020 we had one of the best apparitions of a comet that we have had in a few years. This was comet Neowise. It was discovered  by NASA's Near Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) space telescope on the 27th March 2020. At the time it was a faint 18th magnitude object. By the time I photographed it on the 15th July 2020 it had reached its peak apparent magnitude of between 1.5 and 2.

This picture was taken at 2.32am looking low-down towards north as the sky was beginning to brighten with the dawn. You can see the comet's long dust tail that extended over about 10 degrees at this time. This was a single 10 second exposure (ISO3200) taken on a Nikon D90 at 45mm focal length. This is a long-period comet (with an orbital period of about 6700 years) and so we won't be seeing it again any time soon.

All text and images © Duncan Hale-Sutton 2021

Choosing the sharpest frames - a comparison

In my previous post I put up an image of M81, M82 and NGC3077. During the processing of the 24x30s images that I took on the evening of the 1st February, I explored the option in DeepSkyStacker of stacking just a proportion of the sharpest frames.

The above image shows the galaxy M81 in three different runs of processing the data. The view on the left uses all 24 frames, the one in the middle the sharpest 18 frames (75%) and the one on the right the sharpest 12 frames (50%). You can click on the image to get a closer look at the results. To be honest I don't think removing the less sharp frames makes much difference. You can definitely see an improvement in sharpness from left to right, especially from the 24 to the 18 frames. However, noise in the results is increasing from left to right and what you may think are features, say in the image to the right, may just be noise. So 75% may be a good compromise but as long as you reject images that are trailed or just plain out of focus, then it probably doesn't make a huge difference. Of course, if you take lots and lots of frames then you can be more picky.

One issue with an alt-az telescope like the Celestron NexStar, is that the field rotates from frame to frame and unless your object you are viewing is in the centre of the the field of view, some additional loss of sharpness is going to come from alignment problems at the edge of the frame.

All text and images © Duncan Hale-Sutton 2021

M81, M82 and NGC3077

Last night we briefly had some clear dark skies before a waning gibbous moon and increasing cloud interfered with the view. I haven't used my Celestron NexStar SLT102 for about four years and I was keen to get it going again. I had a rechargeable Sky-Watcher Power Tank for many years, but this has now finally failed and so I have switched to a Powseed 45W variable power adapter which can supply the necessary 12v and it worked very well. The Celestron is computer driven alt-az 4inch f/6.5 refractor. I did a two-star set up on Sirius in Canis Major and Dubhe in Ursa Major.

I spent all the time I had observing M81 and M82 - two galaxies in Ursa Major. They fall into the same field of view in this telescope using a 25mm eyepiece and I was glad that when I requested the telescope to acquire these objects the pointing was spot on first time. However, using a DSLR on this telescope at prime focus can cause the telescope field to move (due to the weight of the camera) and screw up the tracking for a few minutes. When I had reacquired the galaxies it was fortuitous that I also had NGC3077 (another galaxy) in the field of view too.
 

The picture above is the result of 24x30s images (12 minutes) taken at ISO 3200 using a Nikon D90 at prime focus. The images were combined in DeepSkyStacker and the final image (binned x2) processed in Photoshop. M81 at the top of the image is a mag. 6.9 spiral (Sb) galaxy. To the left is M82 (mag. 8.4) which is at a similar distance to M81 (3 Mpc) and which looks anomalous due to a probable recent encounter with M81 which has caused a burst of star formation. To the lower right in NGC3077 and this is a small elliptical galaxy that is also local to M81/M82. It too has evidence of disruption to its structure caused by inter-galaxy interaction (though this image is not detailed enough to show this).

All text and images © Duncan Hale-Sutton 2021