Sunday, January 19, 2014

Size of deep sky objects compared to the Moon

I wrote about this on some previous post, but I felt I'd have to get back to this. Most people, including me few years ago, don't realize how big all the galaxies and nebulae are in the sky. Most common example I've seen is the Andromeda galaxy.

Even if you could see it with naked eye (I've understood it's possible), it won't be more than a tiny smudge. But you won't need much of a camera to capture a lot more of it. Then you're starting to realize.

Here's a comparison of the Andromeda galaxy and the Moon. I took some photos of the Moon with a 200 mm lens, the same I use to photograph Andromeda. I then measured the size of the Moon and resampled a bigger photo (effective focal length 2400mm) to match that size. Resized Moon was then pasted next to Andromeda.

Wikipedia says the apparent size of Andromeda is 190' by 60'. 190 arc minutes is about 3.2 ° so a lot bigger than I measured from that photo. This is the amount I was able to catch on camera. (NOTE: I had mistakenly measured the size to 4.0 °. Now this is fixed.) Moon was on perigee when I took this so it should be about 30 arc minutes or 0.5 °

Here's another. Great Orion Nebula M42 with the Moon placed next to it. M42 is actually visible without any equipment almost everywhere. It's the Orion's Sword, three stars below Orion's Belt. From this photo you can see there's a bit more than three of them. The one on left is the top one on the sky.

Now just imagine if you could see all those galaxies and nebulae with your naked eye.