Question

The average distance between the earth and the sun is called

• A. astronomical unit
• B. light year
• C. parallactic second
• D. none of these

Answer 1

The correct option is A

astronomical unit

The explanation for the correct option:

(A) Astronomical unit

1. An astronomical unit is the unit of length.
2. The average distance between the earth and sun is called an astronomical unit.
3. One astronomical unit is equal to $1.5\times {10}^{11}\mathrm{m}.$

The explanation for the incorrect option(s):

(B) Light year

1. A light-year is a distance traveled by light in one year.
2. It is denoted by the symbol 'ly'.
3. $1\mathrm{ly}=9.46\times {10}^{15}m$

(C) Parallactic second

1. Parsec or parallactic second refers to the distance at which an arc of length equal to one astronomical unit subtends an angle of one second at a point.
2. Parallactic second is used to measure the astronomical large distances to objects outside the solar system.
3. $1\mathrm{parsec}=3.1\times {10}^{16}m=3.26\mathrm{ly}.$

Hence, the correct option is (A).