Thursday, May 17, 2012

Project Zero Zero for the Non-Scientist

For those supporters of mine that aren't scientists, this post is to explain to you "in English" what the Zero Zero project is.

One of the things that I've been a strong advocate of for a very long time is what is called astronomical surveys.  The basic functions of surveys are to dedicate a telescope or set of telescopes to digitally photograph a large portion of the sky with a long enough exposure time to allow us to see very faint astronomical objects, and to make multiple observations of the same objects or patches of sky.

Why are astronomers so interested in seeing faint things in the sky?  Well, it has to do with data (or image) quality and quantity.  The quality of the images of astronomical objects generally improves as the exposure time is increased.  This allows astronomers to obtain the best possible data for further processing and analysis.  The old saying "garbage in, garbage out" applies here, so the better the input data, the better the final results are going to be.

The quantity of astronomical objects found increase as the exposure time increases.  In the case of surveys, this gives astronomers a LOT to work with.  In this first of my projects, my goal is to do a general survey of all objects within a very small field of view -- about 1/4 of a square degree.  This is about 1/4 of the size of the full moon.  A long exposure of a portion of the sky this size will result in thousands of objects being revealed.

I will be primarily using data obtained from the Sloan Digital Sky Survey, which I will hereafter refer to as 'SDSS3'.  The goal of this project is to do a general survey of all objects in a 1/4 square degree area centered on a certain location in the sky.  The name of this project, Zero Zero, indicates that location.  Astronomers have overlaid a grid onto the sky much like latitude and longitude here on Earth.  The east-west grid lines indicate Right Ascension and is measured in Hours, with the range being from 0 to 24.  The north-south grid lines indicate Declination and is measured in Degrees, with the range being from -90 (the south pole) to +90 (the north pole).  The location in the sky of this project is Zero hours Right Ascension and Zero degrees Declination.  Hence the name, Zero Zero.  This general survey will give me a 'lay of the land' and act as a jumping off point for other more detailed projects.

There are two major things I'll be doing in this project.  First is Photometry.  This is measuring the brightness of these objects using different color filters.  In SDSS3, all images have been taken with five different color filters named 'u', 'g', 'r', 'i', and 'z'.  If you've ever seen a rainbow, these color filters correspond to different colors in the rainbow.  The 'u' color filter looks violet, the 'g' filter looks blue, the 'r' filter looks orange, the 'i' filter looks red, and the 'z' filters looks VERY red.  Why is it interesting and useful to measure the brightness of these objects with different color filters?  Because if I compare the brightness of a star, for example, using the 'u' filter (the violet one) and compare it to the brightness of the 'z' filter (the very red one), I see that they're not the same!  Why is that?  Because the star I'm measuring has a particular temperature.  If the brightness of the star using the 'u' filter is higher than the brightness of the same star using the 'z' filter, then I can generally conclude that the star is very hot.  If it's the other way around ('z' brighter than 'u'), then I can conclude that the star is quite cool.  The "bluer" the star, the hotter it is; the "redder" the star, the cooler it is.  Who cares what temperature the star is?  Well, knowing the temperature is a jumping off point.  From this point, I can make a good first guess as to how big the star is (it's 'mass'), what its age is, and how far away it is.  I can also begin to get a sense of what the star is made of.  More on that a little later when I talk about spectroscopy.  One of the things I'll produce is what's called a 'color-color diagram' or a 'Hertzprung-Russell diagram' which will look something like this:

A typical Hertzsprung-Russell Diagram
Each of those little dots represents a star.  Notice that the dots aren't just randomly scattered, but that there are clumps and patterns.  Pretty cool, eh?  This means that there are certain relationships that these stars all have.  Some of them are large, bright, and red (the Giants and Supergiants), some of them are small, faint, and blue (the White Dwarfs).  Most of them are 'Main Sequence' stars which are very similar to our sun (medium size, medium brightness, and yellow).  Stars live out most of their lives in the Main Sequence, but as they age they change into Giants or Supergiants, and then finally White Dwarfs.

So as you can hopefully see by now, what I'm eventually going to get is a really good sense of what kinds of objects I'm dealing with.  How many white dwarfs stars?  How many giant stars?  How many main sequence stars?  Then for each of them, I'll have temperature, mass, and distance.

The other part of this project is called Spectroscopy.  A spectrum of a star like our sun looks like this:
A typical spectrum with Hydrogen and Helium lines
You'll notice first that it looks a lot like a rainbow.  On closer inspection, you'll notice that there are a lot of dark black vertical lines.  These are called 'absorption lines'.  Each of those lines indicate a specific element, like hydrogen or helium.  The spectrum above is showing both 'hydrogen lines' and 'helium lines.'  What this means is that this star has hydrogen and helium in it!  So now, with spectroscopy, I can know what this star is made of!  Very very cool.  By studying the spectrum of a star, I can get to know it much better than with photometry.  All stars are much more complex than to just contain hydrogen and helium.  Most stars have EVERY element represented and have very complicated spectra.  Here is a fairly crude spectrum of our sun:
Spectrum of The Sun
You can see pretty well that there are a LOT of dark lines.  Each of those represent a certain element.  Once those elements are identified, I'll know more precisely what the stars are made of.  This is how I get to know the star, which is the whole point of this project.

SDSS3 provides some spectra, but not a spectrum for every object detected.  Taking spectra is very difficult and they simply don't have the time or technology to do this for everything.  But nevertheless, I'll take the spectra that I can and run them through my analysis and get a list of elements as well as other characteristics I've already mentioned.

Another part of this project is Temporal, or to see how these objects change over time.  SDSS3 has images and spectra of the same object taken at many different times.  This allows me to determine if any changes have taken place.  This is very exciting because one of the things that astronomy has NOT done very effectively is watch things over time and see if they change in any significant way.  Most people tend to think (if they consider it at all) that astronomical objects don't change very much and if they do it takes a very long time.  The reality is that there is SO MUCH ACTION in the universe happening every second that it would be impossible to keep track of it all.  If you don't believe me, take a nearby example and look at what our sun is doing:
  • It's rotating, which means we're always seeing something new
  • It has constantly changing sunspots and sunspot cycles
  • Massive coronal mass ejections of one magnitude or another are happening daily
Now -- what's the difference between our "ordinary" star and all of those other billions of stars?  Nothing.  They're all doing pretty much the same thing as our sun is.  The difference is that they're all so far away that they appear to not be changing.  Just boring points of light in the sky.  But they are as dynamic and interesting as our own sun and very worthy of study -- if for no other reason than to put our own sun into a context that allows us to understand it better.

All of what I've said above about stars also goes for the other kinds of objects I'll find in this survey: galaxies and 'unknowns'.  I'm especially thrilled with the prospects of taking a good hard look at the objects that SDSS3 has named 'unknowns'.

Here, finally, is an image taken from SDSS3 of the Zero Zero field of view that I'll be working on:

The Zero Zero Project Field of View with approximately 9467 detected objects

Well there you go!  This is a general outline of what the Zero Zero project will be about.  I hope you enjoy watching me progress through this and discover what exactly I'm dealing with in this very small patch of sky.

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