Skip to main content

Stacking in Astronomy

Stacking, as the name suggests, is the process of putting one picture on top of another. there might be varied motives behind why one would do this. In the context of astronomy and astro-photography, stacking is done in-order to reduce the noise in the picture and achieve the actual diffraction limited resolution images and to negate the effects of the atmosphere. 

As is known, the earth's atmosphere is very turbulent and an unknown/un-noticed effect is that light bends when it passes through this turbulent atmosphere. while it might not be obvious naked eye, the effect of a turbulent atmosphere is quite obvious when you look at a planet or a star through a telescope.

Here you can see an example of the effect of of turbulence on pictures of the moon.
                             -  source (i didnt ask for permission though) 

As you can clearly see, these pictures are not consistent with each other. 
You can read up this article on Astronomical Seeing to better understand the other effects of atmospheric turbulence while doing Astro-Photography.

Understand that Atmospheric turbulence is a random thing i.e the it's effects cannot be perfectly predicted (which might help us negate it from the pictures) but in most cases it's random.
And as you can understand by now, if we were to take multiple pictures of the same object, it will appear differently in each of these pictures.

Now if we were to 'stack' all of these pictures one on top of another and average them, you can assume that the overall noise in the image is reduced as the original source always remains constant but the effect of turbulence is random (from basic statistics). And viola, we have achieved the primary objective behind stacking.

While in real life, stacking isnt quite as simple as averaging over a number of pictures.
The reason for this can be because of in-efficient tracking (incorrect polar alignment , sidereal rate) or there might be other kinds of noise introduced into a picture due to the CCD used etc etc.
And there are quite a lot of methods to stack by as well.

One of the different methods used in stacking is Lucky Imaging  is one of the different methods used to stack by. you can read up more about it here and here

And there are quite a few (free) software outthere as well which can stack for you.
Some of the best ones are - 

Deep Sky Stacker - as the name suggests, is to stack deep sky images.
Registax - for planetary and solar images. It's awesome :)
IRIS is one of the few advanced programs. havent used it myself. yet.
you can find a couple of other ones here.

While Fitswork is software doesnt stack for you, it is useful in Image Processing post stacking.
And aberrator is an interesting software to understand the effects of turbulence on a specific image.

PS - as you might or might not've noticed, the stars move in the night sky and taking pictures of the same planet or star isn't quite easy. which is why telescopes which are tracking enabled are used, using which, you guessed it, you can track the motion of the star and take pictures of the exact same patch of sky.

i suggest you contact your nearest amateur astronomer for more information. 

Popular posts from this blog

Animation using GNUPlot

Animation using GNUPlotI've been trying to create an animation depicting a quasar spectrum moving across the 5 SDSS pass bands with respect to redshift. It is important to visualise what emission lines are moving in and out of bands to be able to understand the color-redshift plots and the changes in it.
I've tried doing this using the animate function in matplotlib, python but i wasn't able to make it work - meaning i worked on it for a couple of days and then i gave up, not having found solutions for my problems on the internet.
And then i came across this site, where the gunn-peterson trough and the lyman alpha forest have been depicted - in a beautiful manner. And this got me interested in using js and d3 to do the animations and make it dynamic - using sliders etc.
In the meanwhile, i thought i'd look up and see if there was a way to create animations in gnuplot and whoopdedoo, what do i find but nirvana!

In the image, you see 5 static curves and one dynam…

on MOOCs.

For those of you who don't know, MOOC stands for Massively Open Online Course.

The internet is an awesome thing. It's making education free for all. Well, mostly free. But it's surprising at the width and depth of courses being offered online. And it looks like they are also having an impact on students, especially those from universities that are not top ranked. Students in all parts of the world can now get a first class education experience, thanks to courses offered by Stanford, MIT, Caltech, etc.

I'm talking about MOOCs because one of my new year resolutions is to take online courses, atleast 2 per semester (6 months). And I've chosen the following two courses on edX - Analyzing Big Data with Microsoft R Server and Data Science Essentials for now. I looked at courses on Coursera but I couldn't find any which was worthy and free. There are a lot more MOOC providers out there but let's start here. And I feel like the two courses are relevant to where I …

On programmers.

I just watched this brilliant keynote today. It's a commentary on Programmers and the software development industry/ecosystem as a whole.

I am not going to give you a tl;dr version of the talk because it is a talk that I believe everyone should watch, that everyone should learn from. Instead, I am going to give my own parallel-ish views on programmers and programming.
As pointed out in the talk, there are mythical creatures in the software development industry who are revered as gods. Guido Van Rossum, the creator of Python, was given the title Benevolent Dictator For Life (BDFL). People flock around the creators of popular languages or libraries. They are god-like to most programmers and are treated like gods. By which, I mean to say, we assume they don't have flaws. That they are infallible. That they are perfect.
And alongside this belief in the infallibility of these Gods, we believe that they were born programmers. That programming is something that people are born wit…