Tag: science

Jupiter Problems

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!

Mare Crisium

The few clear nights recently have been dominated by a near full moon. You know what that means by now, more moon pics!

I’ve highlighted the Mare Crisium (“Sea of Crises” – who came up with these names?) on this full moon from the night of 15th Dec. It’s the dark patch on the top right of the red rectangle.

P1070719mareCrisiumRectSml

https://en.wikipedia.org/wiki/Mare_Crisium

I wouldn’t think close ups during a full moon would be that interesting. But a few days later, with the shadows beginning to grow on the surface, zooming in is a bit more fun. Here’s a close up of Mare Crisium from 17th Dec. I’ve tried to up the contrast a bit and bring out a bit of detail. Hopefully not too much. If you exaggerate the detail too much then the picture stops looking natural and it becomes very obvious that it’s been manipulated.

Fans of Star Trek: the Next Generation might be interested to know that one of the craters in Mare Crisium is named Picard. Not, it has to be said, after Jean Luc Picard, the captain of the Enterprise, but another Jean Picard, the 17th century French astronomer.

https://en.wikipedia.org/wiki/Jean_Picard

To give you a sense of scale. Picard crater is 23 km across. So about the size of a large town or city. The whole Mare Crisium is about 550 km across – roughly the size of England.

Three days later, on the morning of 20th Dec, Mare Crisium had disappeared into the shadows. The terminator between night and day had moved west. I’ve highlighted the area with the yellow rectangle.

The closeup from that night is centered on the large crater Theophilus between Mare Tranquillitatus to the north and Mare Nectaris to the south.

https://en.wikipedia.org/wiki/Theophilus_(crater)

None of these pictures are likely to win any prizes. But bear in mind they’re taken with a relatively cheap (by astronomy standards) 6″, entry level telescope, and a second hand mirrorless camera. Neither of which are designed for astrophotography. I’m still trying to see just how far I can push such modest equipment. I suspect the real limit is my location in the heavily light polluted Southend-on-Sea.

Any dark skies next week should be mostly moon free. So I have to start planning what to look at.

And if you managed to get this far, Happy Winter Solstice!

Jupiter

Jupiter is beautifully placed in the southern sky at midnight just now, with no moon to spoil the show. You might remember my previous effort to capture it was not a great success. Since then, I’ve picked up a new x2 magnifier for my scope. (Called a “Barlow” in telescope-speak.) I got it for £20 on Ebay, which I consider a bit of a bargain. I’ve no idea if it was responsible for any improvements. There are a myriad of factors that can affect a picture on any one night. But here are the old and the new compared, with the new picture on the right.

jup20Nov28nov

This isn’t what you actually see through the telescope. It’s heavily cropped. The original picture looks more like this. This is a 1/60s exposure at iso 1600.

I don’t normally save “raw” images on the camera. But that night I accidentally had that option switched on, and I’m glad I did. Just a reminder, most images on the web are jpeg type files, or similar. These are compressed images. But the compression algorithm is lossy, it doesn’t preserve all the original information. All the images you see above are based on jpeg originals.

This can work very well for every day pictures in bright light. However, for high magnifications, every bit of detail is important. Raw images save every bit that is captured by the camera. And what a difference it makes. Here they are compared, with the raw image on the right.

As you can see, there’s a lot more detail in the raw compared to the jpeg image. This feeds through the image processing. I took a dozen images in rapid succession and stacked them using my favourite photo processing program, called “Siril”. This is the result (raw on the right).

And here’s that final image close up.

Given the cheap equipment, and basic processing, I’m fairly chuffed with this.

Having said that, Jupiter is by far the easiest planet to photograph. More massive than all the other planets combined, and able to swallow 1,000 earths whole, it presents an easy profile to photograph in the night sky. Mars is tiny in comparison, Saturn is much further away, and Venus is just a featureless, cloudy blob. Initial attempts to photograph them haven’t been an outstanding success so far. I’ll let you know if my efforts improve.

Meanwhile, back in the Andromeda galaxy. No telescope this time, just an old Carl Zeiss lens I found in the cupboard, This was only a brief test, iso 3200 4s x28, so under2 mins total exposure. Based on the result, this might be worth playing with a bit more.

Comet Tsuchinshan–ATLAS

Last night, finally, I managed to get some pictures of the comet that’s being dominating the astronomy news for the last couple of months. Until now it’s always been below the horizon or behind clouds.

I struggled to find it at first even with binoculars. I was expecting a naked eye object, but in the end it took a camera to reveal it.

So here it is, looking west from my back garden in Southend at about 7.30 last night.

P1220678iso3200_0p5_cropLvlSml

This is a cropped and slightly enhanced version. The original looks more like this.

(The comet’s near the bottom in the middle of the picture.) 0.5s exposure at ISO 3200.

And through the telescope.

Again, this has been slightly enhanced. The original is a bit darker.

2s exposure, ISO 3200. These are single frames, so no stacking.

The comet should still be visible for a while, although I’m told it will fade rapidly. As you can see above, it’s already not that bright.