How do we know the distance of stars? If we look east and see a star that is 100 million light years away, then look west and see a star that is 500 millions years away, how can we tell the difference?

Md Ariful Islam

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Md Ariful Islam

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Near bye stars..
standard candles. variable stars.
Type !a supernova.
for details read Wikipedia cosmic distance ladder.\
link

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If Proxima Centauri is the next nearest star to Earth after the sun and it is 4.2 light years, does that mean every star we see in the night sky is farther away than 4.2 light years?

Its visual magnitude is about 11.0

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One estimate is that there are 1010 stars in the Milky Way galaxy, and that there are 1010 galaxies in the universe. Assuming that the number of stars in the Milky Way is the average number, how many stars are in the universe?

I assume that your 1010 means $10^10$. Then the number of stars is simply $10^10*10^10=10^20$.

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How do you find the parsecs and light-years away a star is from the parallax angle? For example, Sirius has a 0.379s parallax angle. How would you get the parsecs and light-years away?

For your long-term-memory: If $alpha$ radian is the parsec angle, the formula for distance = 1/$alpha$ AU. Here, $alpha$=(0.379/3600)($pi$/180) radian.=1.8374 E-06 radian. So, d=1/1.8374 AU=544000 AU. Unit conversions: In lu...

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How often do stars explode in the universe? Are there so many stars that there are millions exploding all of the time?

It has been estimated that in our Milky Way galaxy there is a supernova explosion every 50 years. Given that the Hubble telescope has detected some 150 billion galaxies, this...

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How do us humans know that there are millions of other galaxies? If galaxies are millions of years apart, how do scientists know that there are billions of other galaxies and that andromeda is the closest?

There are a ton of extremely powerful telescopes both here on Earth and in space that is capable of looking billions of light years far. And we can see a...

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If a star is 1000 light years away, how long would it take for us to see light given off from the star?

Light year is the distance traveled by light in one year. Light travels in vacuum 300,000 kilometers per second.

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Edwin Hubble discovered the universe was expanding by measuring the light of distant stars, and by showing that those distant stars were moving further away from the earth. If this is so, then why is the Andromeda Galaxy moving closer to us?

Andromeda is being pulled apart by the expanding universe. But the gravity between the Milky Way and Andromeda is strong enough to overcome this expansive force. Gravity is pretty...

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Why are there so many dwarf stars (red and white) among the nearest stars, but none among the brightest stars?

There is a different story for each type of dwarf star that we cannot see. if you are considering Proxima-Centauri, Proxima-Centauri though is the closest Star to but at the...

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Is it true the light we see from the sun and stars is millions of years old?

Many stars and Galaxies are very far away t he light takes millions of years to reach us. THe light from the stars of Andromeda galaxy is 2.5 million years...

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Star A has a parallax of 0.04 seconds of arc. Star B has a parallax of 0.02 seconds of arc. Which star is more distant from the sun? What is the distance to star A from the sun, in parsecs? thanks?

The relationship between a star's distance and its parallax angle is given by $d = 1/p$, where the distance $d$ is measured in parsecs (equal to $3.26$ light years) and...

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