14

No. There is no consensus. The discrepancy between the predicted big bang nucleosynthetic abundance of Lithium 7 and the measured value can be summarised as follows. If we take what we know about the the baryonic mass density of the universe and the Hubble constant, we get a self-consistent picture between the cosmic microwave background, observations of ...


11

H$\delta$ absorption is formed when hydrogen in the level $n=2$ is excited to $n=6$. To get strong H$\delta$ absorption lines you need large amounts of hydrogen in the first excited state $n=2$ and a radiation field that contains large numbers of photons with an energy equal to the difference between the $n=6$ and $n=2$ states. These requirements are ...


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 Ca triplet in the near infrared are extremely strong resonance absorption lines. They are by far the strongest features in the near infrared spectra of cool G,K,M type dwarfs and giants, which will be the majority of the stars observed by the Gaia RVS. The Ca triplet lines are so strong that even in low metallicity halo stars, that have little Ca in ...


9

Looks like you can measure the cosmological redshift of quasars using that equipment and an 14" reflector: http://www.rspec-astro.com/sample-projects/ (halfway down the page) So the answer appears to be yes, you can do it, assuming that page isn't a total fabrication. Seems plausible to me: the redshift of that quasar is sizable at 0.15 (though that's ...


9

This is a rather broad question and this will not be a fully comprehensive answer. There is no single temperature to the solar corona. The coronal temperature varies by an order of magnitude from place-to-place. It is hottest ($\sim 10^{7}$ K) in magneticloops undergoing flares, which tend to be anchored in low latitude regions. It is coolest (a bit less ...


9

I suspect that the record holder (as of 14/2/2017) is HD 10180 which has at least 7 planets and possible evidence for as many as 9. Lovis et al. (2011) announced the initial discovery based on 190 radial velocity measurements taken over 6 years. The precision of the measurements was 0.3-0.9 m/s. Section 4 of that paper describes how they go about finding ...


7

The ESA states it pretty clearly (although their figure of 855.2 nm is incorrect; it should be 866.2 nm): The RVS wavelength range, 847-874 nm, has been selected to coincide with the energy-distribution peaks of G- and K-type stars which are the most abundant RVS targets. For these late-type stars, the RVS wavelength interval displays, besides numerous ...


7

Light that is not light That's meaningless. All light is electromagnetic radiation. A finite part of the infinitely large range of the electromagnetic spectrum is visible light. So you should talk about EM radiation and to discuss the visible spectrum just say visible spectrum. Stars emit lots of energy at frequencies that are outside the visible range. ...


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

According to Cropper and Katz 2011 part 2.2, the RVS working group considered other bands, but the ~850 nm band is relatively unaffected by absorption in the Earth's atmosphere, facilitating ground-based preparation and follow-up. In addition to the strong Ca II triplet, this band is rich in lines enabling study of astrophysical quantities other than radial ...


6

This was a coronal mass ejection. Those 1973 astronomers weren't looking at the picture correctly. They didn't have the tools at that time to look at the picture correctly. Coronal mass ejections (the term used now) were only discovered a couple of years prior to that picture taken from Skylab, via the Orbiting Solar Observatory 7 satellite. Those early ...


6

When we look at spectral lines in a star's spectrum, we're actually looking for absorption lines, not emission lines. A star's spectrum usually resembles that of a black body, continuous and smooth. However, there are elements in the star's atmosphere that absorb some of the emitted light; these create characteristic absorption lines in the spectrum we ...


6

What you're missing is that the resolution of a prism isn't high enough to resolve the relatively narrow spectral lines. What's more, the light that gets generated by fusion reactions doesn't reach the surface of the sun for a very long time, and it get's scattered and split a large number of times along the way, removing any signature of fusion from their ...


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

As freelanceastro noted in his answer: Yes, you can measure the cosmological redshift of quasars with simple equipment. The page he referred to is not a fabrication. (See the article on amateur astronomical spectroscopy in the August 2011 issue of Sky & Telescope.) Many amateurs have made this measurement with a variety of instruments, including a ...


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 lines show as either peaks above the black body emission (for emission lines) or troughs below the black body emission (for absorption lines). Though stars more often have absorption lines and nebulae emission.


5

Yes - quite a few isolated neutron stars have been observed, where any magnetospheric emission or accretion-related emission is either negligible or has been otherwise separated. As you suspect, this emission is thermal in nature. Neutron stars are roughly approximated by black bodies but, like "normal" stars, they do have atmospheres and strong magnetic ...


5

No, the blue and red shift of stars is not possible to detect with the naked eye. There are a couple of reasons for this. First the effect is slight: even for an object moving at thousands of km/s (way faster than stars in the milky way move), it is only a tiny change in hue. Next, since the light of stars is a mixture of many different colours (a black body ...


5

Two questions are asked here. Sean Lake addresses the first - there is nothing unusual about sunlight; it's spectrum contains many dark absorption lines due to various chemical elements. You just need a reasonably high spectral resolution (high dispersion) in order to see them. The light from the Sun comes from the photosphere. We do not see what is going ...


5

That's a region of recent star formation in the disk of NGC 4302. Regions of recent star formation include short-lived, high-mass O and B stars, which are blue (because they're hot) and luminous enough to outshine the (redder) lower-mass stars that are also present. If you look carefully at the image, you can see hints of blue light from other parts of the ...


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

They have both 21cm and mm-wave observations for those systems. Caption to Fig.1 The hollow squares correspond to two 21 cm and molecular absorption systems. By "system" they are referring to sets of absorption features caused by multiple clouds of material along the line of sight to a single quasar. Each cloud imposes its own set of absorption features....


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.


4

Temperature ($T_{eff}$) can be quite tricky to determine accurately as it interrelates to a number of other fundamental measurements. Firstly, remember that the spectrum we observe from stars are pin-point, they give us the entire overall result and not a specific location or part of the star. We need to dissect the various parts to arrive at the ...


4

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 ...


4

There isn't a lot of engineering here. Just use a grating dense enough to give you a comfortable angle. Less dense grating (fewer lines per mm) means a more shallow angle and narrow spectrum, and that can be harder to use. Super-dense grating might be expensive and fragile. Stay somewhere in the middle - you'll have to do a few trial runs on your own, see ...


4

All this means is that you need to bin your spectra in equal intervals of log wavelength for each pixel to be a constant interval in velocity. First consider the case whereeachpixel is worth a constant interval in linear wavelength. Here we have $$ \frac{\Delta \lambda}{\lambda} = \frac{\Delta v}{c},$$ and the $\Delta v$ represented by each pixel depends on ...


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