How to capture star spectra in your backyard


Hello! Have you ever wanted to do some
science with your telescope and astronomical camera or maybe just a
standard DSLR without a telescope at all? It’s really easy to do. I’d like to
introduce you to this which is the Star Analyser grating. Now the grating comes
mounted in this filter cell which you then just screw directly onto your
eyepiece or your static FITS camera or astronomical video camera or, as I said,
just a plain DSLR. When you do that, it splits the light so that you can study
the stars just like professional scientists do. Now before I show you how
we mount this grating, let’s take a look at some of the results
that you can easily get. Let’s start with one of my favorites. Each of these Star Analyser spectra is
a different OBAFGKM star. At the top are the hot type B stars and
at the bottom are the cool type M stars. This was captured with just a 9 inch
telescope and an astronomical video camera. But you could do the same with a
DSLR or FITS camera too. Notice that each star spectrum is a little different
because they’re all different temperatures. For example, this hydrogen beta line is
strongest on this type A star, which is our familiar alpha Lyra. Now don’t worry, you don’t need to become an astrophysicist to do this kind of thing. It’s really pretty simple and there’s a
lot of help on the web. And, you know what? This kind of thing makes a great high
school science project. Ok. Let’s look at a different example now.
This is a very hot star called a Wolf Rayet star. Because it’s at the end of its life,
it’s shedding its outer shell. That means we can see into the core of
the star. With just a DSLR and a Star Analyser, you can capture this star
spectrum. You’ll be able to see the glowing carbon
from the core. And you can detect the effects of the massive stellar winds as
the star blows off its outer shell. My experience is that when I capture
this kind of data, my understanding of the stars grows in leaps and bounds. Now here’s an example that’s
much closer to home. With a Star Analyser on almost any astronomical
camera, it’s easy to detect… the methane in the
atmosphere of Neptune. Just a few decades ago, this kind of thing was only possible with professional instruments. Now, all it takes is a small telescope and
astronomical camera. So this is an animation of an exploding
star. A Type II supernova happens when the star’s internal furnace runs out of
fuel and its core collapses under the force of gravity. A shock wave from the
implosion rushes outward and the the star explodes. For a short while it’s brighter than all of the stars in the galaxy. With just an eight inch telescope and a cooled FITS camera, just 15 minutes of integration time will capture the
supernova spectrum. You can easily determine what type of
supernova it is and, by observing the Doppler shift in
the spectrum, you can measure how many millions of miles per hour its shell is racing towards us. Ok, so here’s our last example.This one is a quasar: a black hole with an accretion
disk. It’s four trillion times brighter than
the Sun … but it’s also billions of light-years away. It’s so distant that we can detect the
red shift due to the cosmological expansion of the universe. With the same
equipment you’d use on a supernova, you can easily capture the quasar
spectrum and then measure its redshift. From that you can determine its distance. So … this stuff isn’t hard.
Amateurs do it all the time… And those are some pretty exciting
examples, aren’t they?! Now just for a moment, let’s look at how we use the Star
Analyser grating to get these kinds of results So this is a typical wide-field view of
Orion’s belt when viewed through the Star Analyser grating. We can see the
individual stars. And on each star we can see a rainbow called a “spectrum.” The Star
Analyser grating and splits the starlight (just like a prism would do) to
create each spectrum. And each spectrum contains information
about the star. Once we’ve captured that image, we then look at it in software. We’re going to look at a program named
RSpec here. Now there on the left is the star. And on the right is the
spectrum. Now you don’t need to use a color camera. That just happens to the
image that we are using here. We’re pretty far zoomed in. Now what the
software does is plot the intensity of this region over in the graph here on
the right. That peak there is the star. And this region over here is the
spectrum. We won’t get into a lot of detail here, but that dip right there in
the graph corresponds to a gap in the rainbow here. And by analyzing this graph,
we can tell all sorts of information about the star: its temperature, some of
the materials that are on it, the star type. It’s really easy to use. You know, what always amazes me is just
how easy it is for amateurs with such simple equipment to capture and
interpret the spectra of stars. It doesn’t require dark sky sites or a
lot of aperture. I’ve seen amateurs do this with a six
inch refractor and a webcam. So I’ve got here an astronomical video camera. The neat thing about this camera is that
when you use a video camera with the RSpec software, the spectrum is live. That means you’ve got a lot of
opportunity to do public outreach and education. So, when we take the Star Analyser
grating, we just screw onto the nose piece of our camera. Most cameras come
with the nose piece that’s about the right length. There’s nothing exact about
[It doesn’t have to be exactly placed.] Now you might be using a static, cooled
FITS camera It may have a nose piece that works for
you … or perhaps you’re using a filter wheel. You can mount the grating in a
filter wheel and the site talks more about how to mount it so it’s
approximately the right distance from your sensor. And finally we’ve got our
beloved DSLRs. Now it’s easy and there’s two ways to use a DSLR. The first is to
use this thread adapter and thread it on to our camera’s lens cap threads and then just thread our grating right onto it Now we’re ready to go! We can capture
spectra. We can piggyback the camera. We could even use the camera on a static
tripod without tracking and capture the spectra of bright stars. Now there is a second way that a lot of
us use our cameras and of course that’s without the lens – we’re using our
telescope as the lens. And for that, if you have your t-ring on the camera
already, you just use a different adapter that we have that goes into the t-ring
threads. And then you thread the SAtar Analyser into it and then mount this on
your telescope. So like I said when we started, wouldn’t
YOU like to do some science with your telescope or your DSLR?! It’s easy to do and it’s inexpensive.
Check out our site. We love to answer questions and I look forward to hearing
from you that you’ve captured your first star spectrum!

8 thoughts on “How to capture star spectra in your backyard

  1. All we know about universe is done like this , using light splitting methods then measuring that light , its 1920s tech or do astrophotography or DSO ,like Hubble space telescope , all things you can do in your back yard today , ppl half a century ago , believed they walked on the moon

  2. Wow, I have to get me one of those eventually, didn't knew it was so easy and inexpensive to do spectroscopy with modest equipment.

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