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Multiple choice physics constellations and galaxies light year evolution and end stages of stars in the world of stars

The $6563 A^0 H _\alpha$ line emitted by hydrogen in a star is found to be red-shifted by $15 A^0$. The speed with which the star is receding from the earth is

  1. $3.2 \times 10^5m s^{-1}$

  2. $6.87 \times 10^5m s^{-1}$

  3. $2 \times 10^5m s^{-1}$

  4. $12.74 \times 10^5m s^{-1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Wavelength of $H _\alpha$ line, 
$\lambda=6563A^o$
$=6563\times10^{-10}$


Redshift observed in star $(\acute{\lambda-\lambda})=15A^o=15\times 10^{-10}$

Let the velocity of the star with which it is receding away from the earth be v.
Red shift relation, $\acute{\lambda}-\lambda$=$\dfrac{v}{c}\lambda$

$=\dfrac{c}{\lambda}\times (\acute{\lambda}-\lambda)$

$=\dfrac{3\times 10^8\times 15\times 10^{-10}}{6563\times 10^{-10}}$
$=6.87 \times 10^5m s^{-1}$

Multiple choice physics constellations and galaxies light year evolution and end stages of stars in the world of stars

What is known as Astronomical Unit (AU)?

  1. Average distance between Earth and Sun

  2. Average distance between Sun and Moon

  3. Average distance between Moon and Earth

  4. Average distance between Earth and Star
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Average distance from the centre of the Earth to the centre of the Sun forms the astronomical unit (AU). It equals to around 149.6 million kilometres.

Multiple choice physics constellations and galaxies light year evolution and end stages of stars in the world of stars

The method of measuring distance to stars beyond 100 light-years is

  1. Capheid variable stars

  2. Heid variable stars

  3. Lowheid variable stars

  4. None
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The brightness of the stars changes over time. The difference in the brightness over time allows calculating the distance to the star. This is the cepheid variable stars method that is used to measure the distance to stars beyond 100 light years.

The method of measuring the distance to stars beyond 100 light-years is  Cepheid variable stars

Multiple choice physics constellations and galaxies light year evolution and end stages of stars in the world of stars

Which is the another unit used by astronomers for measuring distance to other parts of Milky Way Galaxy?

  1. Km

  2. Light year

  3. Parsec

  4. Meter
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Units used in astronomy by astronomers are an astronomical unit, light year and parsec.

another unit used by astronomers for measuring the distance to other parts of Milky Way Galaxy is Parsec

Multiple choice physics constellations and galaxies light year evolution and end stages of stars in the world of stars

How can Cepheid variable stars helpful to figure out true brightness?

  1. These stars change their brightness over time

  2. These stars lower their brightness over time

  3. These stars raise their brightness over time

  4. None
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The brightness of the stars changes over time. The difference in the brightness over time allows calculating the distance to the star. This is the cepheid variable stars method that is used to measure the distance to stars beyond 100 light years.

These stars change their brightness over time