The “terminator” in this case is not some sci-fi sounding robotic killer. Instead, it is the line that marks the sunlit from the dark part of the moon. As it moves across the moon’s surface each month it has a dramatic effect on what is visible.
Here, for example, is Tycho crater, taken on 11 April.
Tycho is the centre of the large “splash” in the middle of this photo. Large rays of ejected material, resulting from the impact that caused the crater, are clearly visible, extending over a thousand miles in all directions.
Yet when we look at the same crater a few days earlier, the scene is completely different.
Tycho is more to the left in this picture. The rays are much less pronounced, with some of them barely visible. Instead, the crater walls and central mount are much clearer. These two photos barely even look like the same moon.
As I’ve pointed out before, even over a single night, the terminator moves visibly across the moon’s surface. It is this constant interplay of light and shadow that makes photographing the moon so endlessly fascinating.
Here are two very similar pictures of the moon. One taken with my 6 inch Skywatcher reflector and a Lumix GF7 camera. The other taken with the Seestar S50 2 inch refractor.
Do you have a preference? It might not be easy to decide as I’ve tried to make their size, orientation, contrast and colour as similar as possible. Here’s a higher resolution version. (I recommend that the high res pics are viewed on something a bit bigger than a phone.)
I’ll come back to this later. To maintain the air of mystery and suspense, I won’t say yet which picture came from which telescope.
I was hoping to show some splendid pictures of the total lunar eclipse from Friday morning. It was a beautiful clear sky all night with the forecast to remain fine. The moon was full and looked absolutely glorious, all ready to move into the Earth’s shadow. I had both telescopes set up and ready to go (even though my back pain was giving me hell). The S50 was going to do time lapse movies, while the Skywatcher would record high resolution pics. Then, with ten minutes to go, this happened…
And here’s a short movie of the clouds doing their thing, getting in the way.
I waited for about half an hour, hoping that the cloud was just temporary, but it just got thicker and thicker, until the moon was completely obscured. So I put all the equipment away and came back inside. Just after dawn, when the moon had set, the sky cleared again. If I was so inclined, I might suspect that someone was trying to tell me something.
Here are some pics from those who were more fortunate.
Still, we had some lovely clear nights over the last week or so. I managed to enlarge my set of waxing moon phases. Adding in some from January, it now looks fairly complete.
On the night of the thinnest crescent moon, I also took an overexposed shot to reveal the part of the moon in shadow.
And on the night of March the 7th to 8th I took one of those comparison photos that shows the terminator moving overnight.
The waxing moon is the easy bit though. It appears from early evening and usually means going out either just before, or just after, tea. The waning moon is very different. It’s OK getting the initial stages, but the later crescents mean being out early in the morning close to dawn. Let’s see how dedicated I can be.
Now back to the telescope comparison at the top. Personally, I can’t tell a lot of difference between the two when viewed on a web page. However, when you zoom in, the difference becomes more obvious.
In both cases, the right hand picture comes from the larger, six inch, scope. The close up illustrates the much higher resolution that the larger scope is capable of. This is what I’ve found using the smaller smart telescope over the last couple of months. It’s absolutely fantastic for just putting outside and telling it to go take a picture of something. Incredibly easy. It produces amazing results for publishing on the web. But take a closer look and its pictures are all a bit fuzzy. It wets the appetite, making you want to try to do something better.
The larger scope can produce much more detailed pictures, but it isn’t “smart”. It takes a lot of fiddling about to keep it on target and to keep taking images.
Oddly enough, the manufacturer of the smart scope also supplies a lot of higher resolution, and much more expensive, equipment. If this is a clever marketing strategy then I have to say it’s working. I’m looking at their more expensive gear. This little box of tricks, for example, can turn almost any scope into a smart scope.
Look south just after sunset today and you’ll see the unmistakable constellation of Orion.
Follow Orion’s belt left and down and you find Sirius, the brightest star in the sky. Sirius is so bright for two reasons. First, it really is a bright star, shining some 25 times brighter than the sun. Second, Sirius is on our cosmic doorstep. At a mere 8 light years away it’s one our next door neighbours in space.
Sirius is surrounded in our view of the sky by a bunch of light smudges. These are open clusters of stars. A closeup map from Stellarium shows a few of the brighter ones. Many of these are visible with binoculars.
And here are a few of the brightest ones: M46, M47 and M50.
I particularly like M46 because it includes a bright orange foreground star, 140 Pup, a red giant 700 light years away. This contrasts with the main cluster which is nearly 5,000 light years away.
Open star clusters tend to show mainly young, bluish stars. They’re usually regions of recent star formation where the constituents haven’t yet dispersed. We mostly see the brightest members which tend to be blue-white in colour. Their dimmer, yellow-red companions are outshone by these blue-white stars.
M46 has another surprise though. It also includes a planetary nebula, shown near the top left of this photo. It goes by the charming name of NGC 2438.
Again, this is a foreground object about 1,300 light years away. It’s not a true member of the cluster. Planetary nebulae have nothing to do with planets. They just look a bit like planets. They’re the remnants of old stars that have blown off their outer atmosphere and are now illuminated by the remaining core at their center. Given that this is an older star, it should now be obvious that it can’t truly be part of the open cluster M46.
On the opposite side of the sky, I’m still stacking photos of M13, the Great Globular Cluster in Hercules. This is three night’s worth of photos stacked. I’m not sure if adding any more to this will improve the quality or not. Only one way to find out…
Over the last couple of years I’ve been struggling to do a little astrophotography on the cheap. I’ve used an entry level Newtonian with a second hand mirrorless camera, neither of which were designed for the purpose. However, the limitations of the equipment were beginning to show. Attempts to photograph the Virgo galaxy cluster and the Horsehead nebula proved fruitless. The scope and camera had to be controlled independently, so I had to sit beside them outside and monitor everything they do, manually taking individual pictures with no real idea how they would turn out.
So I bought myself one of these, a Seestar S50, one of the new generation of “smart” telescopes.
It’s a bit more money than I’m used to spending on this hobby, but if my first night out with it is anything to judge by then I think it’ll be worth it. And in comparison to some, it’s relatively cheap.
It’s about two feet tall, including the tripod, and weighs roughly the same as a bag of sugar. So you can pick it up with one hand and take it anywhere. It contains a highly quality lens system, a low noise camera sensor, a dew heater to prevent it misting up, a dual narrow-band light pollution filter, a solar filter, an auto-focuser, tracking software and image stacking software. Everything is controlled from a single phone app that, fortunately for me, is almost idiot proof.
I used to spend a considerable part of each night just trying to get things in focus. Sometimes I’d have to repeat each session multiple times just to be sure of getting the focus spot on. The Seestar app has an auto-focus button. I just press that and, as if by magic, within a few seconds everything is in perfect focus.
It seems to have quickly become a tradition that the first thing everybody does with the Seestar S50 is photograph either Andromeda or the Orion Nebula, and I’m no exception. so let’s get them out of the way.
These are pretty much how they came out of the box. I’ve brightened them a bit, probably too much in the case of Andromeda, but otherwise haven’t done any post processing on them. The Seestar also let’s you save the individual image files so that you can do your own selection and stacking rather than rely on its algorithms. I haven’t got around to that yet. The one night I’ve spent with it gave me more data than I previously got in a month. It’ll take me weeks to work my way through it all.
Just to prove that it really could take the pictures that I couldn’t take before. Here’s part of the Virgo cluster of galaxies and the famous horsehead nebula. Again, I’ve cropped and brightened the images very quickly, with no real attention to detail.
The big white blob at the top of the horsehead picture is the star Alnitak, the left hand star in Orion’s belt.
One of the downsides of the Seestar is also illustrated in the horsehead picture. If you look carefully at the right hand side of that image, you’ll see vertical streaks running at an increasing angle down the right hand side. This is because of the type of mount that it uses. It can go up and down and left to right. This allows it to track the positions of objects in the sky. However, if you think about it, objects don’t just appear to move across the sky, they also appear to rotate. The Seestar can’t fully compensate for this, with the result that longer exposures cause the effect you see. There’s a well known way around this, but as this was my first night out I wasn’t going to try anything elaborate.
A couple of more galaxies, Bode’s galaxies and the Triangulum galaxy.
There are a couple of lines across the bottom of the left hand image of Bode’s galaxies. This isn’t a telescope artefact this time, but a plane flying across one of the frames. When I do my own stacking I’ll get rid of this frame.
And now a couple of old favourites, the Double Cluster in Perseus and T Corona Borealis – our unexploded star. The Double Cluster picture is way better than anything I’ve previously taken with my old setup. Despite being one of the largest and brightest objects in the sky, my old telescope often had difficulty finding the Double Cluster. The Seestar uses a technique called “plate solving”. Essentially it compares what it sees with its internal database of stars, figures out where it’s pointing, and moves to the desired location. All with no user intervention whatever.
T Cor Bor has disappeared from the evening sky in the west, but if you wait until about 4 am it rises above the eastern horizon again.
And finally, that sun-with-a-bird picture. This time I’ve included another sun-with-a-bird picture from the next day. When you’re imaging the sun, especially when you take movies over a couple of minutes, it’s actually surprisingly common to see a plane or a flock of birds transit the sun’s disk. Notice how the sunspots move with the sun’s rotation from one day to the next.
My other scope has about ten times the light gathering power of the Seestar, so it isn’t redundant. And it’s got one thing that the Seestar doesn’t have, an eyepiece, so you can actually look at the sky with your eyes rather than a phone. But for sheer convenience and it’s ability to record images, the new box is quite unbelievable. I might even try driving a few miles out of town to escape some of the light pollution in my back yard.
But I’ve saved the best bit for last. As it’s controlled by a single, dedicated, phone app, and you can operate it over wi-fi, I can sit in the comfort of my living room in shorts and t-shirt, glass of wine in hand, and tell the telescope exactly what I want it to do. Then I just sit back and watch as the images appear on my screen. No more shivering for hours outside in the cold. In fact, the telescope barely needs me at all.
I normally stack lots of short exposures. Due to the limitations of my telescope, I need to spend a lot of time re-centering whatever I’m taking pictures of. This is OK for star clusters or galaxies or nebulae. I can spend hours collecting as many frames as I like. These objects barely change over a period of hundreds of years. So I did the same with Jupiter.
This picture was taken on 21 Dec at about 2 am. It’s a stack of about ten frames. It’s OK, but I thought I could improve it by stacking more exposures. But it seemed that the more frames I tried to stack, the worse the result became. What’s going wrong?
It took me ages to figure out the reason: Jupiter has changed! It may seem obvious, but the planet Jupiter rotates. In fact it rotates fast. Despite being large enough to swallow 1,000 earths, it’s day only lasts 10 hours.
This adds another complication when you’re trying to photograph it. For a planet that’s rotating fast it means I don’t have much time. Here’s the same picture on the right. This time contrasted with another, taken 20 mins earlier.
The planet does a full rotation of 360 degrees in 10 hours. 36 degrees in an hour. 12 degrees in 20 mins. 12 degrees is a huge amount.
Even in these low resolution, blurry images you can see that cloud features have moved significantly in 20 mins. Here’s the same comparison again. This time there’s a yellow rectangle highlighting a small collection of three greyish clouds against a brown background. The same three clouds are visible on the right hand image too but have clearly moved.
If only the planet would just stay still while I photograph it!
Platitude of the Day 