AstroSpectroscopy - a type of astrophotography

[geyes30]

Recently I started working with spectroscopy, using a DIY grating and a software called RSpec. Since the imaging of the spectra is a type of photography, I thought I'd post it here. However, if this is out of place, please let me know.

Anyway, it is easy to make the grating. Details are here: https://theamateurengineersg.wordpress. ... ctroscopy/

The camera with grating installed:
2018-08-31-01-11-21 by Cyrus Beh, on Flickr

Here's the spectrum of Vega, before instrument calibration
vega-with-hydrogen-balmer by Cyrus Beh, on Flickr

And here it is after calibration
Vega Emission Lines Labeled by Cyrus Beh, on Flickr

Usually, stars exhibit absorption spectra. However, yesterday I came across Gamma Cassiopaeiae, also known as Navi. This star has emission lines at H-alpha and H-beta!
Navi Emission Lines Labeled by Cyrus Beh, on Flickr

Lots of fun, and science anyone can do.

[geyes30]

One of the biggest discoveries in astronomy was that of the nature of nebula. In the early days, it was unclear whether nebulae were under-resolved stars or gas clouds. It was believed that the former was the more likely explanation. So, it was a big deal when it was demonstrated that the nebulae had distinct wavelengths, i.e. they were emission sources with discrete wavelengths, and not continuum emitters. Planetary nebulae are suitable for this sort of experiments. Here is an image of M57, the Ring Nebula, taken with a diffraction grating.

M57 Ring Nebula Spectrum Image by Cyrus Beh, on Flickr

The orange arrow and oval show the position of the diffracted image of the nebula, which shows not a smear, as with stars, but rather a fairly well-defined image. This was the clue that they were in fact gases excited by nearby stars. To determine the wavelength of the emitted light, and hence the type of gas involved, we can calculate it using the spectroscope.

M57 Ring Nebula Spectrum by Cyrus Beh, on Flickr

The wavelength of the diffracted image is around 500 nm, corresponding to the O-III emission line. That is, the gas can be identified to be oxygen, though erroneously identified as a new element dubbed "nebulium" in the 1860s when first observed.

[kochu]

Hi geyes30,
Nice to see your posting
I was also considering getting the software Rspec and their 100 lines Grating .
It was good to see from your posting that there is a cheaper alternative and thanks for the same. I will also buy the one through AliExp as it is so much cheaper.
How did you cut the rectangular grating?.
Admin can also consider making a "Spectroscopy" section in the forum.
Kochu/3-9-18

[geyes30]

Hi Kochu,

Glad it was helpful to you. Just a word on the cheap grating though - the efficiency seems to be a bit low. That is, the direct star image is quite bright compared to the diffracted image. Although it makes a serviceable spectroscope, the SA-100 may yield better results.

The grating is made of PET, which is quite a soft plastic. So I just snipped a tiny triangle off all four corners. That gets them small enough to glue onto a filter retaining ring.

[kochu]

Thanks
No harm in trying the PET grating first.
Kochu

[kochu]

Hi,
Did you buy the 100 L one . It is only available in 36 x 18 mm size.
Kochu

[geyes30]

Yes I think that's the one I got. It doesn't cover the whole filter, but of you orientate it right it should cover an entire sensor, up to Micro4/3rds.

[kochu]

Thanks,
Then I think I will have to go for SA 100. No choice . My Camera sensor is APS C Type and FF
Kochu