# Tag Info

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Possibly you are labouring under the misapprehension that the number of photons is somehow a conserved quantity? That isn't true, there are more photons at any given wavelength when you are deeper into the star, because there is a temperature gradient. Cooler material further out is less emissive because fewer atoms are in excited states. The temperature ...

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There are some technological issues to solve with putting any large telescope into space - and a space telescope is required at UV wavelengths. It is not possible to optimise such an instrument to work at both UV and IR wavelengths because of issues like cooling, mirror coatings and such-like. The simple angular resolution limit of a telescope goes $\lambda/... 14 You're correct in that the sharp dropoff is simply because there are very few planned major telescopes operating in the UV range, whereas there are a substantial number planned in the infrared range. As I mentioned in my answer you linked to, CHARA and the EELT, two of the top planned infrared/visible projects, will use new adaptive optics technology, making ... 13 There are other ways of getting emissions than just direct thermal radiation. Most of it happens through plasma interactions in the solar corona and atmosphere than in the chromosphere. This review paper names bremsstrahlung, gyroresonance, cyclotronmaser, and plasma radiation as sources, each with their own brightness temperature way above 6000 K. (See also ... 11 In order to be in hydrostatic equilibrium, high surface gravity atmospheres have higher pressures at the same sort of temperatures. That means the density of atoms and ions is higher. If the particle density is higher then there is more chance of interactions between the particles. In particular, collisions between atoms perturb their energy levels and ... 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 ... 9 A galaxy is obviously going to be much more distant than the stars. On the other hand the galaxy contains a lot of stars which will contribute to the overall spectrum. Whether the galaxy or a star will be brighter will depend roughly on the ratio of$N/d^2$, where$N$would be the number of stars and$d$would be the distance to the galaxy. What your plot ... 8 This was a hard one to answer, primarily because of the difficulty in tracking down information. The Observations of MU69 The extended mission for New Horizons involved adjusting its orbit to do a close fly-by of a Kuiper Belt Object (KBO). The annoying part about this was that they needed to find one first! Ground based observations were unsuccessful due to ... 7 The programs I am aware of that you could use do require some programming expertise to operate. I would recommend looking at either IRAF (or PyRAF, which uses Python to interface with IRAF), or SPECTRE. Unfortunately, I'm not aware of a "black box" solution where you can just press a button and go. SPECTRE is written in FORTRAN77 and is quite easy to use ... 7 The crusts of neutron stars will contain "super-heavy", neutron-rich nuclei. This is an inevitable consequence of the high density material, the accompanying degenerate electrons (that block$\beta$-decay) and what we know about nuclear physics. However, the only things that contribute to a neutron star's observable spectrum are materials within a few cm ... 7 You need to compare it with the spectrum of a similar galaxy at a known redshift, that would probably enable you to identify features with known rest wavelengths. If you can find such a template, then the best way of estimating a redshift for a galaxy spectrum like this, consisting of mostly weak and blended absorption features, is to cross-correlate your ... 6 Because the wavelength ratio of the lines remains constant despite any cosmological red shift. For example, if the redshift is$z$, all the lines are shifted redward in wavelength by a factor$(1+z)$. This means that a pattern of lines can still be recognisable. We also have a pretty good idea of what the spectra should look like, which chemical elements ... 6 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 ... 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 Conrad is almost right. It is true generally that if a Galaxy is close enough to take spectra of individual stars (e.g. luminous supergiants) then it is not far enough away to be regarded as part of the "Hubble flow" and so applying Hubble's law to this star, or its host galaxy, would not yield a reliable distance in any case, but would reflect the "peculiar ... 5 There are plenty of software and tools available to do what you want: IRAF, by NOAO; MIDAS which is basically very similar to IRAF but developed by ESO; in Python, either astropy or pyRAF (to use IRAF with a Python interface). I would go with some Python tools (Python is more versatile than IRAF or MIDAS that are much more "single-purpose" oriented), to ... 5 Yes, there is are two python modules called astropy, and astropysics that both claim to have spectral analysis tools. As a reference, here is a link for resources for astronomers for the python programming language. 5 This is a spectral energy distribution (SED). Since astronomical objects don't emit light a single frequency an SED tells you how much emission you're getting across a range of frequencies. "log" indicates it's on a logarithmic scale$\nu$represents frequency in Hz (e.g.$log~\nu=12$is$10^{12}$Hz) Jy is a unit of specific flux density$f_{\nu}$is the ... 5 An arc spectrum is one produced by a discharge lamp where the discharge is through ionised gas, in the case of He-Ar a mixture of Helium and Argon, which produces a predictable line emission spectrum. They are often used to provide a calibration spectrum for spectrometers. 5 The spectral type of an object is almost entirely determined by the temperature of its photosphere. ie Saying something is type M3.5 is just a measure of its surface temperature. An M3.5 brown dwarf is at a very similar temperature to an M3.5 star. Brown dwarfs begin their lives as hot balls of gas and gradually cool with time. They start off as M-type ... 5 Realistically, no - there are too many stars with the same spectrum. The pulsar idea is a good one, though. There is a reason our location relative to some bright pulsars was sent out on the Voyager plaques: we are confident that a civilisation finding one could then find our sun, and us, as the pulsar rates are unique enough. 5 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 ... 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 ... 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 I think you can understand that factor as follows: When photons lose energy, they're spread out over a larger wavelength range. Since there is a fixed number of photons, that means that the number of photons per observed wavelength bin decreases by a factor of (1+z), and hence the flux density, which is really what$f_\lambda\$ is, decreases by this factor.

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The lines that appear in a stars spectrum mainly reflects its temperature not its composition, see here O-type stars start out with the same sort of composition as other stars, that is they are mainly H and He (approximately 75% and 25% by mass) with traces heavier elements.

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Actually the method described on Wikipedia is not the method that is meant by Spectroscopic Parallax. To determine the spectroscopic parallax, you'll need a spectrum of the star and measure the widths of the spectral lines. Compact stars have higher surface gravity, which means that their spectral lines are broader. This means that the radius of the star can ...

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While the answer by @zephyr is extensive, unresolved images of a very distant Kuiper belt object distant body over a short arc of it's orbit through a single filter can not be used to calculate a color. Further, contrary to the claim in that answer, there are indeed a series of measurements alternating between visible and infrared filters! The Sci-News ...

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