What Fake Astrophotography Can Teach Us

What Fake Astrophotography Can Teach Us

The New Zealand Herald has an article today about a cool and very popular image of the Moon positioned perfectly within a radio satellite, produced by astrophotographer Chris Pegman: Supermoon image goes into media orbit

Image by Chris Pegman
Image by Chris Pegman

The article talks about how there has been debate online about whether or not this could be taken without resorting to Photoshop. It concludes that “the verdict was that it might be, but it would require an incredible amount of planning” but this isn’t strictly correct.

The apparent rotation of the Moon changes as it travels through the sky. When it rises, it will appear to be “on its side” relative to when it is at its zenith, and when it sets it will have rotated further still.

This is most obvious with a crescent Moon. Depending on if it’s waxing or waning, the Moon will rise with the crescent facing either down or up, then when it’s at its zenith the crescent will be facing sideways, and as it sets it will have rotated around further. Of course, the lit side of the Moon always faces the Sun. It’s the fact that the Earth rotates beneath us that makes it look like the Moon is rotating as it travels across the sky.

Here’s an example of this which I took with my phone in July, showing a waning crescent Moon shortly before sunset:

We can see from the lunar maria (the dark areas) that the Moon in Chris Pegman’s picture is rotated how it would be if (when viewed from the southern hemisphere) it were near its peak, not near the horizon, so his picture couldn’t be produced without artificial manipulation.

Mark Gee is a fantastic astrophotographer from Wellington. In October he captured a time lapse of a full moon rising, in which you can clearly see that angle of the Moon is not the same as in Chris Pegman’s image when it rises: Supermoon rises over New Zealand timelapse.

There’s a Twitter account called Fake Astropix, which tweets fake astronomical images with the reasons why they are recognised as fake (well, as much as can be given within a tweet).

I find these reasons can be very educational and thought provoking. For example, it’s impossible to take a photo from Earth where the Sun and Moon don’t appear to be roughly the same apparent size. Also, the full moon can’t appear next to the Sun in the sky (remember the lit side faces the Sun). So “debunking” these fake astronomical images can be a good educational exercise that makes you think a bit more carefully about how things work in our solar system.

Do you have any fake astronomical images that you can share, along with the reason why you can tell it must have been faked?

Have you seen any astronomical images that you think might be fake but you’re not sure? Share them here and let’s investigate, and see if we can learn something.

Advertisements

Movement of the Moon

If you were up late last Wednesday, you’d have gotten the chance to watch the second total lunar eclipse this year. A lunar eclipse occurs when the Earth moves directly between the Moon and the Sun, therefore blocking the light to the Moon and making it turn dark.

This is very cool to watch, especially if you get a good look at the Moon during totality, when it is in the darkest part of the Earth’s shadow known as the umbra. At this point, the only sunlight reaching the Moon is that which is refracted through the Earth’s atmosphere. For the same reason as why sunrises and sunsets appear a lovely reddish colour, this light is also quite red, and as the Moon reflects some of this light back at us it appears a dim bronze colour.

This is one of my favourite space facts, and I find it quite poetic – you’re looking at the reflected light of all the sunrises and all the sunsets in the world, all at once. There are many spectacular photos of this effect online if you care to search for them too. But this is not what I want to write about in this article.

If you were watching Wednesday’s eclipse from Auckland, as I was, you’d probably have been disappointed to see that it was quite cloudy for the duration of totality. However, you were probably able to get a good view of the first part of the eclipse, when the Moon is moving into the outer part of the Earth’s shadow known as the penumbra.

Greg O’Beirne managed to put together a great compilation of this part of the eclipse:

Photo by Greg O'Bierne
Photo by Greg O’Beirne

As you can see, it looks rather like the Moon is having a bite taken out of it. In this compilation the position of the Moon is held roughly constant but in reality it’s the Moon that is moving here. During a lunar eclipse, we are given the rare opportunity to directly observe the Moon’s orbital motion.

Because the Earth is spinning, the Moon always appears to move across the sky from east to west (in the southern hemisphere, this effectively means it is moving right to left). The time it takes to move across the sky varies with the time of year, but it takes roughly 25 hours to do a full circuit.

Because of the Earth’s spinning, generally the only way we can usually observe the Moon’s orbital motion is by looking for it at the same time every day. If you do this, then instead of watching it migrate east to west over a day, you’ll see it move slowly from west to east over a couple of weeks.

In order to watch the Moon move directly, it would be possible to watch it move relative to a stationary background object. The stars could serve this purpose while the Moon is up at night, although generally it’s bright enough that it’s very difficult to see any nearby stars. The occultation of Saturn earlier this year, which I watched from home through my telescope, gave me a chance to observe its movement against the relatively stationary planet. Like with the stars though, you simply wouldn’t be able to observe this with your naked eye.

A solar eclipse is also an opportunity to directly watch the Moon’s orbital motion, as we can compare it to the Sun, as its movement is fairly negligible for everyday purposes when compared with that of the Moon. The problem there, of course, is that you can’t look directly at it without damaging your eyes. A lunar eclipse gives you the same opportunity except, unlike a solar eclipse, you can watch it directly.

If we ignore the Earth’s spin, then both the Sun and the Earth’s shadow (which, of course, must always be directly opposite one another) each take one full year to move the whole way across the sky. Because the 365 1/4 days in a year is very close to the 360 degrees in a circle, we can say that they move roughly 1 degree every 24 hours, or half a degree every 12 hours. This sounds pretty slow, but half a degree is roughly the size of the full Moon so it isn’t entirely negligible.

It takes about an hour for the Moon to move fully into the outer part of the Earth’s shadow, so in this time it moves roughly 1/12th the diamater of the Moon. For the sake of simplicity, let’s ignore this motion as well. Below I’ve put together a (rather clumsy and very imprecise) animated gif, using the images from Greg O’Beirne’s great compilation as its frames, to show this motion of the Moon holding the position of the Earth’s shadow roughly constant:

Lunar Eclipse Oct 2014 Animation

If you want to view this for yourself, the next lunar eclipse visible from New Zealand isn’t too far away. You may have read that there won’t be another total eclipse visible from New Zealand until 2018, but on the 4th of April 2015 there will be a partial solar eclipse in the evening where you’ll be able to see this. In the meantime, have a look up at the sky occasionally and notice where the Moon is (using landmarks as a guide to remember its position will help). If you make it habitual to do this at a specific time (I do it every day when I leave for work, for example) then you’ll be able to watch the Moon’s slow movement backwards across the sky.

Stargazing

As I mentioned in an earlier post, after looking up at the night sky through binoculars for the first time over my summer holiday, I decided to buy a telescope this year. On the 27th of January, I went to see a show at the local observatory, Stardome, and ended up talking to one of the staff about the telescopes they had on sale. I came home the excited new owner of a “Celestron Powerseeker 114EQ”.

My new telescope
My new telescope

It’s a “Newtonian” telescope, also known as a “reflector”. It uses a mirror to gather light, as opposed to a “refractor” that uses a lens. The light comes in the front of my telescope and hits a concave mirror 114 mm in diamater at the other end of the tube, where it is bounced back up to a flat mirror near the opening that reflects the light out the side into the eyepiece. I have 3 eyepieces that give 45x, 90x, and 100x magnification.

My first target was Jupiter, which I’d got a brief glimpse of from one of Stardome’s much more expensive telescopes after the show I saw. When viewing it from home, I was thrilled to be able to make out its 4 Galilean moons, and tried taking a photo. It turns out, as you might be able to guess, that holding an iPhone 4 camera up against the eyepiece of a telescope in the dark, then holding it steady and pressing the “take a photo” button without bumping the phone, is actually pretty hard. I got very lucky though, and the first photograph I took clearly showed an overexposed Jupiter and its 4 largest moons:

Jupiter and the 4 Galilean moons. In no particular order: Io, Europa, Ganymede, and Callisto
Jupiter and the 4 Galilean moons. In no particular order: Io, Europa, Ganymede, and Callisto

Some time later, I was also lucky enough to take a recognisable photo of Saturn using the same technique:

Saturn. It appears on its side because of the angle I was viewing it from. Click through to see the full image.
Saturn. It appears on its side because of the angle I was viewing it from. Click through to see the full image.

That picture was taken with the highest magnification eyepiece, which has a lens only about 6 mm in diameter. It was really difficult to hold my phone steady for this, even with the trick I’d learned of using the iPhone headphones’ volume buttons as a remote for the camera app. After this, I decided I should look to see if I could buy an adapter to fit my iPhone directly onto my telescope, but while searching for one I found an article about how to make your own adapter. I didn’t follow the steps in that article, but I did decide to give it a shot. I found a piece of plastic, an old cover for part of a swimming pool pump, that fit perfectly over my telescope’s eyepiece, and put it together with a bunch of foamboard and glue to get the final product. Here are a few pictures of the process:

The first layer
The first layer
The plastic backing
The plastic backing
The second layer
The second layer
The 2 pieces combined
The 2 pieces combined
Trying it out. It was a bit heavy at this stage, and overbalanced my telescope
Trying it out. It was a bit heavy at this stage, and overbalanced my telescope
Cutting it down to size
Cutting it down to size
All trimmed down. After this I sanded the edges and it was good to go
All trimmed down. After this I sanded the edges and it was good to go

Using this new adapter and some astrophotography image processing software called Registax that lets me combine multiple images or frames of a video to form a single clean image, I’ve been easily able to take some clear images of Jupiter, the Moon, and Saturn:

Jupiter, with some of the cloud bands clearly visible. Click to see the full image.
Jupiter, with some of the cloud bands visible. Click to see the full image.
The waxing crescent Moon. Click to see the full image.
The waxing crescent Moon. Click to see the full image.
Saturn, rings and all. Click to see the full image.
Saturn, rings and all. Click to see the full image.

Registax also allows for a bit of processing to remove noise and sharpen the image. I’m not sure what I think of this yet, as I’m pretty much flailing blindly and to be honest it feels a bit like cheating, but here’s what came out the other end when I applied some of its filters to that Saturn image:

Processing image of Saturn to remove noise and sharpen it. Click to see the full image.
Processing image of Saturn to remove noise and sharpen it. Click to see the full image.

I also took some photos of Mars, but they’re all horribly overexposed and not really worth looking at. I’ve been having trouble seeing anything aside from just a circle of light when it comes to Mars. It’s tough using an iPhone 4 as a camera. It’s not possible to manually change settings like focus or exposure, and in order to take photos and videos of Jupiter that weren’t overexposed I had to lock the camera’s settings on the brightest part of the Moon (done not by tapping to focus like usual but by holding my finger on the spot for a second or so). Luckily Jupiter and the Moon are quite close in the sky at the moment so that wasn’t too much effort, but moving the telescope back and forth between the Moon and Mars was quite annoying. I’m sure there’s a better way that I’m yet to find. It possibly involves buying a decent camera.

One other thing I was finally able to do last night is resolve the Alpha Centauri system (the outermost of the 2 “pointers” that show the way to the Southern Cross) as a binary star system. I wasn’t able to photograph it though, the stars still appear very close together and my phone overexposed them to look like a single star. I guess that’s a challenge for another night.

I’m also quite looking forward to the upcoming total lunar eclipse on the 15th of April. Although I’ve read that the Moon is meant to turn a dark red during the totality of the eclipse, I’m not really sure what to expect when it comes to viewing or photographing it, which I find pretty exciting.