Hot answers tagged

11

Here is a link to a diffraction grating that can do what you want. It is mounted in a 1.25" filter ring that attaches to an eyepiece, or to most astro cameras. I believe they also sell adapters for other cameras and software to extract spectra from the photos. Here is a link to a spectra of Vega that I took with a 120 mm refractor using the Star Analyser ...


10

The Sloan Digital Sky Survey Data Release 15 contains over 4 million spectra of both galactic and extra-galactic origin from the multi-fiber spectrographs. Of these spectra, 0.7 million came from the original spectrographs during the SDSS-I/II Legacy Survey and the remainder from the upgraded spectrographs as part of the BOSS survey during SDSS-III (see SDSS ...


7

The crusts of neutron stars will contain "super-heavy", neutron-rich nuclei. This is an inevitable consequence of the high density material, the accompanying degenerate electrons (that block $\beta$-decay) and what we know about nuclear physics. However, the only things that contribute to a neutron star's observable spectrum are materials within a few cm ...


6

You can probably get most if not all of your questions answered by perusing the main DESI web site, which I encourage you to check out. There is, for example, a nice video describing the assembly of the main focal plane elements (the fibers and the associated robot positioners) here. But in simple terms: the circular focal plane is divided into ten wedges (...


5

In general, you can't. If obtaining spectra in regions where there is expected to be a spatially varying background then you either need to do long-slit spectroscopy so that you have a good measurement of the ISM contribution either side of your source, or you do integral field spectroscopy with the same idea. The problem is that the line strengths for the ...


5

Supplemental to @PeterErwin's answer, some more details on the five thousand "robots". Each fiber has a circular "patrol area" with a diameter of 12 millimeters, and these are located on a hexagonal array with a pitch (nearest neighbor distance) of 10.3 millimeters. Motion is implemented with eccentric axis (Θ–Φ) kinematics. Instead of x-y or r-Θ which use ...


5

If you only had that single line, you would be unable to differentiate them. This is especially true of redshifted objects where we couldn't tell the actual wavelength of an isolated peak. But a good spectrograph will give you information over a range of wavelengths. Each element has multiple lines. It is the overall pattern of relative strengths that ...


4

Yes, nebulae can often have very distinct colours. What produces those colours can depend on what elements are in the nebula material and what the temperature and density are. Generally speaking, green colours in a nebula are due to forbidden transitions in ionised Oxygen, though can feature the hydrogen $\beta$ Balmer line. Red colours can be due to ...


4

TL;DR: (1) we don't need to go very far to measure the spectrum of Earth's reflected light: a satellite in orbit around the Earth could easily do that; however, (2) detecting the reflected light of an Earth-size planet is extremely difficult: we currently use other techniques with much greater success. The Wikipedia article on how scientists detect ...


4

So the two observed lines must be two of the three suggested lines, red-shifted by the same amount. That means the ratio of their wavelengths will be unchanged, so we need two of the suggested lines whose wavelength is close to the ratio $404.7/317.6$. It's easy to check that only the first two are close to that ratio, so they must be those two. So the ...


3

It looks like the floating "g-98" is just an extension of the header of the plot (made by IRAF), which has wrapped around the image for lack of room on the right-hand side. Looking at the N0 plot, we see that the header should read NOAO/IRAF V2.10.4EXPORT perry@sparky.sao.arizona.edu Mon 06:04:51 03-Aug-98 which just contains information about the software,...


3

As an addendum to Chappo's very good answer, I'll note that people have indeed used satellite and spacecraft observations of the Earth to estimate what a similar exoplanet might look like (assuming we had better telescopes and instrumentation than we currently do). For example, the NASA Deep Impact spacecraft (which had visited the comet Tempel 1 in 2005) ...


2

Disclaimer: this is speculative, since no images of a black hole have been taken with enough resolution in visible light. The black hole represented in the movie Interstellar is moderately realistic with the knowledge we have at present. In fact, the movie makers asked astrophysicists to contribute. From the article Gravitational lensing by spinning black ...


2

A glory is a rainbow-colored bullseye appearing directly opposite the Sun due to diffraction by water droplets of a certain size. From an airplane, you can sometimes see this effect surrounding the airplane's shadow. As the NASA article explains, the polar orbiting Terra satellite's scan pattern transformed the circular rings into elongated ovals.


2

I know what an optically think/thick medium is... Okay so this isn't much more complicated. A medium or material can be optically dense or opaque at one wavelength, but fairly transparent at a different wavelength. If you look at the dark plastic window on a remote control for a TV or other appliance, you can't see through it. It's optically dense at ...


2

Steve Linton answers correctly that the line ratios must be (nearly) identical and hence identifies the two lines as Lyman $\alpha$ and C IV, but it's not true that the two obtained redshifts are suspiciously alike. In fact, when you do the calculation, you get (from $z \equiv \lambda_\mathrm{obs}/\lambda_\mathrm{rest} - 1$), $$ \begin{array}{rcl} z_{\mathrm{...


1

Thanks to @PearsonArtPhoto's comment data with 1 cm^-1 wavenumber resolution is available in the link labeled MODTRAN data here: https://www.nrel.gov/grid/solar-resource/spectra.html Here's a quickie plot and script for the downloaded ASCII data. There are six columns of spectral intensity data (Watts/m^2/nm) with labels 'MCebKur', 'MChKur', 'MNewKur', '...


1

There are several online sources of spectra (eg SDSS), but they usually just provide a FITS file with data, or a plot vs wavelength without any annotation. Of course, you could use the NIST atomic spectra database to identify lines, but that quickly becomes tedious. There are many figures containing spectra for various classes of stars in the book by Gray ...


Only top voted, non community-wiki answers of a minimum length are eligible