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The brown dwarf "limit" is about $0.072 M_{\odot}$ at solar metallicity (e.g. Chabrier et al. 2000) and is composition dependent. It gets a little higher in metal-poor gas and a little lower in metal-rich gas. $0.064 \pm 0.012 M_\odot$ (the third significant figure is superfluous) is within one error bar of that limit, which in itself is only a 68% ...

2

You would have to pay a lot more than buying time on existing instruments. You would have to pay for the construction of new and very expensive instruments You could pay to have copies of the Gaia spacecraft built and sent into orbit around the giant planets in our solar system and/or at their L4 and L5 positions. Thus two or more such observatories could ...

0

I suppose that the International Astronomical Union has rules for naming stars in multiple systems. I believe the usual rule is to describe the brighter star as A and the dimmer star as B, which works well as long as neighter star is very variable. Thus the brighter star in Alpha Centauri is Alpha Centauri A and the less bright star is Alpha Centauri B. ...

0

The purpose of the notation is to indicate how the system is physically constructed, to indicate which stars orbit which - especially useful in hirachically organized stellar systems. So both ways are correct as their meaning is understood. The notation I encounter most often is the first one you indicate: indicating with capital letters the systems which ...

0

So I use the following logic: Define 'red', 'green' and 'blue' light in terms of the wavelength ranges those colours encompass (from here) Calculate the average spectral radiance across each wavelength range, for a defined temperature Define the RGB value to be the relative ratios of each colour's spectral radiance with 255 defined as the colour with the ...

3

If present, an a (or b or ab) do not refer to spectral peculiarities but are part of the luminosity class definition explained further up on the page. Occasionally, letters a and b are applied to luminosity classes other than supergiants; for example, a giant star slightly less luminous than typical may be given a luminosity class of IIIb, while a ...

0

I live far out in the country under very dark skies. I walk my dogs every night after midnight. Summer temps in the 90's. Winter temps get down to -40 deg. I have been doing this for over twenty years. As an amateur astronomer I do pay close attention to the sky whenever I am outside at night. No romance in the seasons. If anything the skies are the darkest ...

1

To add to Rob Jeffries answer, there are a couple of other factors. Meteorology: when a cold front passes over a location, relatively warm cloudy conditions are followed by rain, and the cooler clearer skies. It may also be windier, which can lead to the brighter stars twinking more, which probably emphaises the clearness. It is also thought that the ...

4

If the Sun collided with another star about the same mass, then its mass would be slightly less than 2 solar masses, as some material would be ejected away from the merger. This would result in an A-type star, as the merger's mass is about 2 solar masses. A good example of a 2 solar mass star is Fomalhaut A, which is an A3V star. Therefore, this merger ...

3

Yes. Clear skies allow the Earth to cool more effectively at night. If there are clouds, these re-radiate some portion of the infrared flux from the Earth back towards the ground, keeping it warmer.

2

Because you're asking for a spacecraft, there is some wiggle room because spacecrafts can make adjustments. An orbit around the Moon isn't stable both because of proximity to a much more massive body (the Earth) and due to the Moon's unusual lumpiness, but spacecraft can and have orbited the Moon when the orbit of least change is selected around the Moon ...

2

Possibly a planet could be habitable to humans while having some layers of chemicals or dust in its atmosphere that block out all visible wavelengths of light. However, someone else would have to design such an atmosphere. Perhaps the "planet" could actually be a giant exomoon oriting a giant exoplanet in another star system. And possibly all the ...

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What if the star was surrounded by a large dust cloud? Then the visible radiation would get stopped, while the dust cloud would eventually heat up and emit the infrared. The cloud could be orders of magnitude larger than the star, which means that the energy into the dust cloud is still equal to the energy out, just in different frequencies. In fact, the ...

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The minimum temperature of an object classed as a "star" is something like 2700 K. Such an object, although emitting the bulk of its radiation in the infrared, would still emit something like a few per cent of its energy at visible wavelengths. Note that the visible and near infrared spectra of cool stars are nothing like blackbodies, so if the ...

2

The English language would seem to offer the phrase "planetless star", which seems adequate to me. However, given that we can't confirm whether there is a ninth planet around our own star, then calling any other star planetless is probably premature.

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The short answer is no. The spectrum of electromagnetic radiation emitted by a body follows a curve that depends on its temperature. This is called its “blackbody radiation.” Even for objects whose blackbody curve peaks in the infrared (heat) portion of the spectrum, there is a small but significant portion of the curve also in the visible spectrum. You can ...

1

This answer is addressed at the level of the question for learners not professionals. Because our solar system planets travel in near circles people imagine that is somehow the natural condition. But it is a tricky question. First, we should imagine gravity as an upturned trumpet shape and a planet as a ball rolling along such surface. Depending on the ...

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Who can say for sure? I guess the physics in Universe Sandbox is not good enough. What I would say though is that if you have a "protostar" that contains a higher proportion of heavy elements than a usual star, then the threshold for ignition of hydrogen will be lower than 75 Jupiter masses (e.g. How large can a ball of water be without fusion ...

3

The masses of the two objects are completely determined by a careful measurement of their relative positions on the sky over decades, combined with an accurately known distance. There is no degeneracy in this solution. For a given orbital period and separation of the two objects, the masses are entirely determined. If Sirius B were not a massive white dwarf ...

3

The spectral classes (O, B, A, F, G, K, M) and their 10 subtypes (0 to 9) were initially meant only as differentiators of spectral type. Annie Jump Cannon was the creator of this system. Through her work for/with Edward Pickering, she ended up classifying nearly a third of a million stars over a few decades. She (and many others) did not realize that this ...

4

The UV luminosity of a galaxy can be calculated, given a stellar population. This population, in turn, can be calculated given an initial mass function (IMF), i.e. the distribution function of stellar masses. In this case, the UV luminosity should be linearly proportional to the star formation rate (SFR), sometimes written $\Psi$. The UV is primarily emitted ...

3

From Wikipedia In his 1698 book, Cosmotheoros, Christiaan Huygens estimated the distance to Sirius at 27664 times the distance from the Earth to the Sun (about 0.437 light years, translating to a parallax of roughly 7.5 arcseconds). and It was also in this book that Huygens published his method for estimating stellar distances. He made a series of smaller ...

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Henrietta Swan Levitt was the first person to develop the "standard candle" technique for measuring the distance to stars, while studying Cepheid variables around 1912-1913. Of course, the standard candle technique just extends the parallax technique to farther distances; in order to figure out how bright Cepheid variables are, Levitt had to know ...

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As far as I know direct parallax measurements are the only way to directly measure the distances to stars. Once parallaxs of hundreds of stars were known and diagrams of the relationship between stellar luminosity and spectral types, such as the Hertzsrpung-Russel diagram, were made, it became possible to estimate a star's absolute magnitude more or less ...

2

Yes. Stars (those objects that are supported by hydrogen fusion) can be as cool as spectral type L2. Brown dwarfs can be as warm as M4/5 when they are young. i.e. there isn't a clear spectral type Vs mass relationship. It depends on age too.

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According to Eric Mamajek's table of main sequence stars, the absolute V-magnitude of zero corresponds to late B-type stars. The values that bracket zero are B8V with $M_{\rm v} \approx -0.2$ and B9V with $M_{\rm v} \approx 0.7$. There is a fair amount of scatter around the main sequence so it is likely that some stars a few spectral subtypes away may have ...

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A star with magnitude 0 would be 85 times brighter than the sun (since Magnitude=-2.5 log(Luminiosity)) Referring to the H-R diagram on Wikipedia shows that there is quite a range of spectral types possible with this luminosity: from B type main sequence stars, and A type sub-giants, such as 4 Sco There are also G and K and M type Giant stars with this ...

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There isn't a one-to-one relationship between spectral type and absolute magnitude. Instead, there is a mean relationship with a fair bit of scatter around it. The reason is that the luminosity of a star of a given effective temperature depends on its composition/metallicity and how far along in its main sequence lifetime it is. Basically, late B-type main ...

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The absolute magnitude quantify the luminosity of an object at a standard distance of $10\,pc$ from earth. For example, in the case you mentioned, Vega becomes dimmer then at its actual distance (about $7\,pc$) . To answer your question, I don't think there is an actual star with exactly 0 absolute magnitude. If there is then, following the formula of the ...

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