# Tagged Questions

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### How do we estimate the amount of $10^{23}$ stars?

Now, I read somewhere, that there are $10^{23}$ stars in the universe. How did scientists estimate this?
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### Do septuple (7), octuple (8) or nonuple (9) star system exist?

The highest I found so far is Castor, a sextuple star system. And there doesn't seem to be any other sextuple star system within at least 100 light-years...
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### Binary Mass Function Plot

Suppose that we have a circular eclipsing binary system with orbital period of $P = 2 \text{days}$, and with one star with a radial velocity of $v_{1r} = 100 km/s$. The other star is to dim for its ...
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### Is there a way to tell what centile of the overall sample a star's mass is in?

One hears that hyper-giant stars like Eta-carinae represent the upper bound on stellar mass at about 130 solar masses. At the lower end there are red dwarfs with as little as 0.075 solar mass. You ...
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### How did all of the heavy elements on earth get here?

I have often read that a first generation star went supernova and seeded our solar system. It is well known that stars that go supernova are the source of elements heavier than iron. I guess I am ...
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### How to explain the existence of heavier elements in Population I stars and in Population II stars contain lighter one

Recently I read Astrophysics Notes where I found a statement that young stars are classified as Population I stars and relatively older one as Population II stars. Population I stars contain ...
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### Calculate the maximum variation in brightness of a star due to the presence of a planet in orbit

Background: As a planet orbits around a star, the star's brightness periodically dims as shown in the following picture. By measuring the variation of brightness, we are able to deduce information ...
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### Quick question on parallax and parsec

I know that 1 parsec (pc) is the distance of star at which 1 AU subtends 1 arcsecond. so $1 pc = \frac{1 AU}{1"}$ Now, if two stars in a binary with a separation of 3" and have a trigonometric ...
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### Rocky Planet in the center of System [duplicate]

We all know that mostly stars are at the center of planetary systems, but is it possible that instead of star there was a rocky planet in the center with stars (and other planets and moons) orbiting ...
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### How are stellar and galactic ages determined?

Being a 4th year undergraduate physicist, you'd think I'd know this! But it's never really taught in any detail, just vague mentions of metallicities and, in galactic case, redshift. So how exactly ...
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### How to measure distances to stars by means of spectroscopic parallaxes?

How to measure distances to stars by means of spectroscopic parallaxes on practice? What is the accuracy of measuring distances using this method compared with distances based on HIPPARCOS ...
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### Relation of fraction of binary stars with spectral class (mass)

What is relation of fraction of binary stars with spectral class (mass)? For example, how many binary stars are among O,B,A,F,G,K,M stars separately?
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### What is the percentage of stars with planetary systems

We have discovered quite a number of exoplanets to date. The Kepler spacecraft has examined 150,000 stars and found 1,059 exoplanets. We know that Kepler, as well as all other exoplanet searches to ...
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### Creating a Star Map

I have a set of data on all the stars (well, to a magnitude of 9 or so) with the values of the following properties: magnitude, right ascension and, declination. Now I'd like to create a planar ...
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### Can the “Milky Way” galaxy be seen by the naked eye in a clear sky?

Is this photo "real"? Are the stars not super-imposed in the image?