Units
Section 1: Basic Understanding of Units in Astrophysics

Units are standard quantities used to express physical quantities.

The International System of Units (SI) is primarily used in astrophysics.

The base units in the SI system include the kilogram (kg) for mass, meters (m) for length, and second (s) for time.

Derived units, such as the Newton (N) for force, are combinations of the base units.
Section 2: Common Units Used in Astrophysics

Astronomical Unit (AU): This is the average distance from the Earth to the Sun, approximately 150 million kilometers.

Light Year (ly): It represents the distance light can travel in a year, approximately 9.46 trillion kilometers.

Parsec (pc): This is equivalent to about 3.26 lightyears, or approximately 31 trillion kilometers.
Section 3: Converting Units in Astrophysics

It’s important to understand how to convert between different units of measurement within the field of astrophysics.

For example, 1 lightyear = 63,241 AU = 0.3066 Parsec
Section 4: Dimensional Analysis

Dimensional analysis is the process of checking the physical consistency of an equation by comparing the units on each side.

It’s important to perform dimensional analysis to ensure your calculations are sound, as incorrect dimensions can lead to nonsensical results.
Section 5: Units in Astrophysical Equations

Familiarity with how units are used in equations is vital. Examples include gravitational force (F = G * (m1*m2/r^2)) where force (F) is in Newtons and radius (r) is in meters.

In Albert Einstein’s equation E = mc^2, mass (m) is in kg, the speed of light (c) in m/s, and energy (E) in Joules.

Note that the units on both sides of the equation should always be equivalent. This is a key component of dimensional analysis.