<p>Depending on the type of camera you use, you may be able to photograph stars without a telescope. I know that there are apps for cell phones that allow you to take long exposures, and there are some point-and-shoot cameras that have a &quot;bulb&quot; setting or allow multi-second exposures, and certainly an SLR-type will allow it. You'll need to stablize your camera thought.</p>
<p>Either way you can use either a transmission diffraction grating (glass or low-cost flexible film-type) or a wedge prism to disperse light into different colors.</p>
<p>If you use a free-standing camera, you can afix the dispersing element in front of the camera's lens. If you are photographing through a telescope you'll need to put it at the camera end. The disperser will usually spread light out by several degrees or several tens of degrees, so if you put it in front of the telescope lens the spectrum will be spread out way too far, <em>unless you are using a very low-dispersion grating or prism specifically designed to be put in front of a telescope!</em></p>
<p>If the disperser partially covers the camera, then you'll get both an image of the star and of the spectrum. That's helpful to identify the position of lines, since you can measure the distance from the undispersed star to each line. If you use a grating that is not blazed or imperfectly blazed, then you'll get both +1 and -1 orders and you can measure the distance between the two appearences of a line without needing the central start, but it will be there anyway because most gratings will pass at least some of the 0th order.</p>
<p>Since the star light is spread out over a much larger area, the spectrum will be much dimmer than the undispersed image, so as you mention, you'll have to overexpose.</p>
<p>There's an example of a commercial product in the question <a href="https://space.stackexchange.com/q/21876/12102">Has anyone seen an actual spectrum of a satellite made by an amateur photographer?</a></p>
<hr />
<blockquote>
<p>I don't mean to advocate a commercial product, this is a handy example, and <a href="http://www.fieldtestedsystems.com/about/" rel="nofollow noreferrer">Tom Field</a> is a contributing editor to <em>Sky and Telescope</em> magazine.</p>
<p><img src="https://i.sstatic.net/bJbGD.png" alt="enter image description here" /></p>
<p><strong>above:</strong> from <a href="https://www.rspec-astro.com/star-analyser/" rel="nofollow noreferrer">here</a>.</p>
<p><img src="https://i.sstatic.net/QflCv.jpg" alt="enter image description here" /></p>
<p><strong>above:</strong> from <a href="http://www.fieldtestedsystems.com/poster/" rel="nofollow noreferrer">here</a></p>
<p>See the FieldTestedSystems' YouTube video <em>How to capture star spectra in your backyard</em></p>
</blockquote>
<p><div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/Fv5fFSacVO8?start=0"></iframe>
            </div></div></p>

CC BY-SA 4.0
2019-09-12T03:46:08.053Z
Cool. I'd love to try this myself! I wonder if it can be used on other things besides stars. I envisage putting a hole in a piece of paper and analysing the sun's spectrum. Or that of a lightbulb or a fire.
zooby
CC BY-SA 4.0
2019-09-12T03:59:43.170Z
@zooby Experiment away! But be really careful with the Sun, don't be like [this guy](https://www.youtube.com/watch?v=CCqwJ7E45W8) ;-) The position of absorption or emission lines only needs calibration of angles/positions. However, the intensity of the spectrum at each point is affected by a lot of factors. Every diffraction grating will have a different transmission (or reflection) efficiency curve as a function of wavelenth, so if you record the spectrum of the Sun you'll see the the roughly-blackbody spectrum severly modified by the grating's own spectral shape.
uhoh
CC BY-SA 4.0
2019-09-12T04:02:37.133Z
If you can compare the spectrum of sunlight to moonlight, you'll see that the moon isn't white, it's albedo in the blue is much lower than in the red. If you can find an incandescent light bulb these days and vary the current, you can see the shape change with temperature. If you use a CCFL or fluoresent light you'll see phosphor lines, and and a whilte light LED will show the blue primary LED light plus the yellow phosphor light. Comparing an old fashioned CRT color TV (white screen) to an LCD display will be nice as well.
uhoh
CC BY-SA 4.0
2019-09-12T04:15:49.323Z
@zooby fyi there was an incorrect link that I've just fixed. The image of the camera comes from https://www.rspec-astro.com/star-analyser/
uhoh
CC BY-SA 4.0
2019-09-12T03:42:49.873Z
2022-02-23T18:27:12.250Z
2022-02-23T18:27:12.250Z
uhoh
<p>For an amateur astronomer, is it possible to measure the spectrum of a star?</p>

<p>I can easily take a photo of a star just by putting a camera on one end of a telescope and over exposing it.</p>

<p>But I would like to measure the spectrum of a star. I imagine I could do some crude approximation by using different filters. But I would like the full spectrum to see what the composition of a star is.</p>

<p>How would I go about this?</p>

CC BY-SA 4.0
2019-09-12T03:35:36.623Z
Suggested reading : [Sky and Telescope article "The Revival of Amateur Spectroscopy"](https://www.skyandtelescope.com/get-involved/pro-am-collaboration/the-revival-of-amateur-spectroscopy/)
StephenG - Help Ukraine
CC BY-SA 4.0
2019-09-12T03:44:05.150Z
@StephenG excellent article!
uhoh
<observational-astronomy><spectroscopy>
What equipment do I need to measure the spectrum of a star?
zooby
# What equipment do I need to measure the spectrum of a star?

(Asked by: username_0 on 2019-09-12)

For an amateur astronomer, is it possible to measure the spectrum of a star?

I can easily take a photo of a star just by putting a camera on one end of a telescope and over exposing it.

But I would like to measure the spectrum of a star. I imagine I could do some crude approximation by using different filters. But I would like the full spectrum to see what the composition of a star is.

How would I go about this?

**Tags:** observational-astronomy, spectroscopy

> **Comments:**
> **username_1**: Suggested reading : [Sky and Telescope article "The Revival of Amateur Spectroscopy"](https://www.skyandtelescope.com/get-involved/pro-am-collaboration/the-revival-of-amateur-spectroscopy/)  
> **username_2**: @StephenG excellent article!  

---

## 1 answers

### Answer by username_2 on 2019-09-12. Score: 6

Depending on the type of camera you use, you may be able to photograph stars without a telescope. I know that there are apps for cell phones that allow you to take long exposures, and there are some point-and-shoot cameras that have a "bulb" setting or allow multi-second exposures, and certainly an SLR-type will allow it. You'll need to stablize your camera thought.

Either way you can use either a transmission diffraction grating (glass or low-cost flexible film-type) or a wedge prism to disperse light into different colors.

If you use a free-standing camera, you can afix the dispersing element in front of the camera's lens. If you are photographing through a telescope you'll need to put it at the camera end. The disperser will usually spread light out by several degrees or several tens of degrees, so if you put it in front of the telescope lens the spectrum will be spread out way too far, *unless you are using a very low-dispersion grating or prism specifically designed to be put in front of a telescope!*

If the disperser partially covers the camera, then you'll get both an image of the star and of the spectrum. That's helpful to identify the position of lines, since you can measure the distance from the undispersed star to each line. If you use a grating that is not blazed or imperfectly blazed, then you'll get both +1 and -1 orders and you can measure the distance between the two appearences of a line without needing the central start, but it will be there anyway because most gratings will pass at least some of the 0th order.

Since the star light is spread out over a much larger area, the spectrum will be much dimmer than the undispersed image, so as you mention, you'll have to overexpose.

There's an example of a commercial product in the question [Has anyone seen an actual spectrum of a satellite made by an amateur photographer?](https://space.stackexchange.com/q/21876/12102)

---

> I don't mean to advocate a commercial product, this is a handy example, and [Tom Field](http://www.fieldtestedsystems.com/about/) is a contributing editor to *Sky and Telescope* magazine.
>
> ![enter image description here](https://i.sstatic.net/bJbGD.png)
>
> **above:** from [here](https://www.rspec-astro.com/star-analyser/).
>
> ![enter image description here](https://i.sstatic.net/QflCv.jpg)
>
> **above:** from [here](http://www.fieldtestedsystems.com/poster/)
>
> See the FieldTestedSystems' YouTube video *How to capture star spectra in your backyard*

> **Comments:**
> **username_0**: Cool. I'd love to try this myself! I wonder if it can be used on other things besides stars. I envisage putting a hole in a piece of paper and analysing the sun's spectrum. Or that of a lightbulb or a fire.  
> **username_2**: @username_0 Experiment away! But be really careful with the Sun, don't be like [this guy](https://www.youtube.com/watch?v=CCqwJ7E45W8) ;-) The position of absorption or emission lines only needs calibration of angles/positions. However, the intensity of the spectrum at each point is affected by a lot of factors. Every diffraction grating will have a different transmission (or reflection) efficiency curve as a function of wavelenth, so if you record the spectrum of the Sun you'll see the the roughly-blackbody spectrum severly modified by the grating's own spectral shape.  
> **username_2**: If you can compare the spectrum of sunlight to moonlight, you'll see that the moon isn't white, it's albedo in the blue is much lower than in the red. If you can find an incandescent light bulb these days and vary the current, you can see the shape change with temperature. If you use a CCFL or fluoresent light you'll see phosphor lines, and and a whilte light LED will show the blue primary LED light plus the yellow phosphor light. Comparing an old fashioned CRT color TV (white screen) to an LCD display will be nice as well.  
> **username_2**: @username_0 fyi there was an incorrect link that I've just fixed. The image of the camera comes from https://www.rspec-astro.com/star-analyser/  

---

