Cosmic Distance Ladder | Astronomical units (AU) | Light year | Parsecs

Cosmic Distance Ladder

No human probe has travelled much beyond the Solar System, yet we are able to measure distances across billions of light-years.

  • Distances between the planets and between stars expressed in miles and kilometers.
  • Cosmic distances are measured in astronomical units, light years and parsecs.
  • Collectively known as the cosmic distance ladder.
  • 1 AU – distance from the Sun to Earth’s orbit, which is about 93 million miles.
  • When measured in astronomical units, the distance from the Sun to Saturn’s orbit, is 9.5 AU.
  • A light year is the distance a photon of light travels in one year (about 6 trillion miles)
  • A light year is how far one can travel in a year if they could travel at the speed of light, which is 186,000 miles per second.
  • Nearest star system Alpha Centauri – 4.3 light years away.
  • Used to find Sun is about 8 light minutes from Earth.
  • This is the unit used when the number of light years between objects climbs into the high thousands or millions.
  • One parsec – 3.26 light years.
  • Megaparsecs (1 million parsecs) – scale of distances between the galaxies.

Astronomers talk about distances in terms of how much a galaxy’s light has been shifted toward longer, redder wavelengths by the expansion of the universe, a measure known as redshift.

Source: The Hindu


Previous Year Question

Which one of the following is a reason why astronomical distances are measured in light-years?

[UPSC Civil Services Exam – 2021 Prelims]

(a) Distances among stellar bodies do not change
(b) Gravity of stellar bodies does not change
(c) Light always travels in straight line
(d) Speed of light is always same

Answer: (d)


Practice Question

The terms “Astronomical units, Light year, Parsecs”, in news are related with:

 
 
 
 

Question 1 of 1

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