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41

The dark lines are colder areas at the edge of the convection cells, where the cooled down plasma sinks towards the inside of the Sun. The yellow parts are where the plasma rises to the surface. Each yellow spot (which is actually the size of a country) is called a granule, and this web-like appearance is called granulation. In the outer part of the Sun (...


22

Usernumber's explanation of the light and dark regions is correct, but there is more detail to be added about granulation on other stars. Granulation is expected on other stars with surface convection zones, but the properties and timescales of the granulation can be quite different. On the Sun, the granules appear and disappear in timescales of 10-30 ...


6

I'll add to @usernumber's answer some graphics. Unfortunately we can't yet "has YouTubes" for some reason so I'll just add the links. There are two videos of the Sun linked in Phil Plait's Bad Astronomy article DKIST first light high-resolution video of solar granules DKIST First light video of solar granulation (wide angle). Here are the same kind of ...


3

LORRI will be used in 4x4 mode, which yields 4-arcsec pixels. The error in positions is unlikely to be better than 1%, or 40 mas, about 200x larger than Gaia's error. NH has a baseline ~20x larger, but this means it still misses Gaia by ~10x. The date was selected for New Moon to help Earth observers find the two targets. There is no Earth analogue for ...


3

There is no lower limit, and as you say, all stars are somewhat variable. However catalogues of variable stars exist, and they can record a wide range of levels of variability. For example, the general catalogue of variable stars lists stars like Alpha Triangulum, with a variability of 0.01 magnitudes. Ultimately a variable star is a star which has had ...


3

There is a candidate ring system around the L-type brown dwarf G 196-3 B. According to Zakhozhay et al. (2017), the brown dwarf has a mass of ~15 Jupiters and a temperature of ~1870 K. They model it as being surrounded by a warm, narrow debris disc located close to the brown dwarf (~1280 K at a distance of ~0.12–0.20 solar radii). ...


3

Even though it arised for historical reasons outlined in the other answers, the distinction between metals and non-metals as defined by astronomers does continue to make sense today. Metals are formed in stars and supernovas, whereas non-metals preexist stars. Therefore, the distinction is relevant when considering nucleosynthesis.


3

Pre- supernova models often characterise the compactness of the core using a "compactness parameter" defined as $$ \upsilon = \frac{(M/M_{\odot})}{R(M)/1000\ {\rm km}},$$ where $M$ is usually chosen to be $2.5M_{\odot}$ and $R(M)$ is the radius within which $M$ is contained. Pre supernova models by Farmer et al. (2016) show that the central $2.5M_{\odot}$ ...


2

While a whole slew of signals will arrive once the supernova actually occurs, from neutrinos to light of all different energies and wavelengths, the outward, visual appearance of the star will not give any surefire clues that a supernova is imminent. But the nuclear reactions powering the star do change over time, and at just 640 light-years away, Betelgeuse’...


2

The premise of this question is wrong: the "Sirius" shaft was not designed to point towards Sirius. Most of the shafts bend (sometimes several times), making it impossible for the light of a star to shine through. Furthermore, the angle of the shaft is not constant, making it possible for the shaft to be pointed towards tens of different stars, depending on ...


2

Try plotting absolute G magnitude (i.e. corrected for the fact tthat all the stars are at different distances) on the y-axis.


2

The projected equatorial velocity of a star (commonly written $v \sin i$, where $i$ is an inclination angle for the rotation axis to the line of sight) is measured by observing the Doppler broadening effect on spectral lines. There is no need to resolve the star. Light from one limb is approaching at $+v\sin i$, whilst light from the other limb is ...


1

TL;DR: the main sequence lifespan of the sun can be increased by a factor of 12.2. Perhaps the most complete astrophysical analysis of stellar engineering for extending Earth habitability is Martin Beech's book Rejuvenating the Sun and Avoiding Other Global Catastrophes (2008). In order to maintain the biosphere the sun's interior need to be mixed (in ...


1

In Equation (16) of the paper you link to, $z$ is the observed redshift. In the first paragraph of section 2.2 The heart of the method is to use a measured redshift, z, to infer a velocity, v(z)


1

With the Gaia Data Release 2, you can plot an HR diagram with a few million stars. From the Gaia website : The data can be accessed in the search tab, where you can specify the columns you want to display (phot_bp_mean_mag and phot_rp_mean_mag). There is a button at the bottom to export the results to a file on your computer. You can then plot one of the ...


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