Tag: light year

Questions Related to light year

The distance of a galaxy from the earth is of the order of $10^{25}$ m. The time taken by light to reach the earth from the galaxy is

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

  1. $3 \times 10^{14}$ s

  2. $3 \times 10^{16}$ s

  3. $3 \times 10^{18}$ s

  4. $3\times10^{20}$ s

Show answer
Correct Option: B
Explanation:

Speed of light, c = 3 x 10$^8$ m s$^{-1}$
Time taken by light to reach the earth from the galaxy is
$\displaystyle t = \frac {10^{25}m}{3\times 10^8m\,s^{-1}}\,=\,3\times 10^{16}s$

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

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

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

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

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

  4. $12.74 \times 10^5m s^{-1}$

Show answer
Correct Option: B
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, $\acute{\lambda}-\lambda$=$\dfrac{v}{c}\lambda$

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

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

The Milky Way Galaxy is about

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

  1. 150000 light years

  2. 200000 light years

  3. 250000 light years

  4. 170000 light years

Show answer
Correct Option: A
Explanation:

Milky way is about 100,000 light years or 30kpc.

The Milky Way Galaxy is about 150000 light years

What is known as Astronomical Unit (AU)?

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

  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

Show answer
Correct Option: A
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.

Which method is used by astronomers to calculate how far the star is?

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

  1. Parallax

  2. Equillax

  3. Purplex

  4. None

Show answer
Correct Option: A
Explanation:

Parallax is used by astronomers to measure the distance between the stars. Parallax is also known as trigonometric parallax.

1 Parsec is:

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

  1. 2.3 light years

  2. 3.3 light years

  3. 4.3 light years

  4. 5.3 light years

Show answer
Correct Option: B
Explanation:

Parsec is a unit of length used in astronomy to measure distances outside our solar system. One parsec equals to around 3.26156 light years.

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

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

  1. Capheid variable stars

  2. Heid variable stars

  3. Lowheid variable stars

  4. None

Show answer
Correct Option: A
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

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

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

  1. Km

  2. Light year

  3. Parsec

  4. Meter

Show answer
Correct Option: C
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

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

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

  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

Show answer
Correct Option: A
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


Distance from Earth to Proxima Centauri, the next nearest star is:

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

  1. 4.24 light years

  2. 5.5 light years

  3. 4.0 light years

  4. 3.5 light years

Show answer
Correct Option: A
Explanation:

Proxima Centauri, a part of a triple star system named Alpha Centauri, is the closest star to our solar system. It is about 4.24 light years away from the Earth.