Light: Crash Course Astronomy #24 CrashCourse Published on 9 Jul 2015


Distances: Crash Course Astronomy #25 CrashCourse Published on 16 Jul 2015

The Treasures of Trappist-1 | Space Time PBS Space Time Published on 1 Mar 2017

Light seconds, light years, light centuries: How to measure extreme distances - Yuan-Sen Ting TED-Ed Published on 9 Oct 2014

The Cosmic Distance Scale by Maggie Masetti from

Three different (much larger) length measuring units are used:
  1. Astronomical Unit (AU) = the distance from the Sun to Earth (1.5 x 10^11 m)
  2. Parsec (pc) = distance of the arc of a sector of angle 1 sec (3.08 x 10^16 m)
  3. Light year (ly) = distance light travels in 1 Earth year (9.46 x 10^15 m)
How far away are the stars and galaxies? How are these distances calculated? from

Every known mass that has been viewed/witnessed in the Universe could include (in increasing magnitude):
  • comets
  • planets
  • stars (single and binary)
  • planetary systems (such as our solar system)
  • constellations
  • nebulae (clouds of dust and gases)
  • stellar clusters (open and globular)
  • galaxies
  • clusters of galaxies
  • super clusters of galaxies

Stars can be grouped together in stellar clusters:
  • open group contains 10^3 stars
  • globular group contains 10^5 stars

Many stellar clusters make up a galaxy. Our galaxy (the Milky Way) rotates with a period of approx 2.5 x 10^8 years.

Beyond the Milky Way, there are billions of other galaxies. Many are grouped together in clusters or super clusters.

Have you spotted the Earth in the solar system? Can you describe nuclear fusion?How does fusion power the Sun?
How does fusion power the Sun ? Science Channel Published on 4 May 2015

Where does the Sun get its energy from? byV eritasium Published on 6 May 2012

How close are we to nuclear fusion from
What is nuclear fusion from

Stars emit an enormous amount of energy through the nuclear fusion of hydrogen into helium:
Star temperatures from hyperphysics

Through analyses, the mass of the products is less than the mass of the reactants. Using E = mc2, we can work out the Sun is losing mass at a rate of 4.0 x 109 kg s-1 (3.9 x 1026 W of energy).
These reactions take place in the core of the star.

Challenge question
1. Describe what Nuclear Fusion is:

2. Describe why this enormous amount of energy radiating outwards does not tear the outer layers of the Sun apart?

As you move from one position to another objects change their relative position.
  • near objects appear to move when compared to far objects
Eg) Close one eye and look at the tip of your finger. When you move it, it ‘appears’ to move further than an object in the distance.
This apparent movement is called parallax and the effect can be used to measure the distance to some stars in our galaxy.
  • closer stars will have an apparent movement when compared to more distant stars.
  • The closer the star is to Earth, the greater the parallax shift

Parallax angle is normally given in seconds (“), not degrees. As all stars are very distant, the parallax angle is always very small.

Interesting article to read from ( June 2017)
1. The mass of the white dwarf star Stein 2051B determined by observing the changing position of another closely aligned star ('The bending of light by gravitation').
2. Dr. Kailash Sahu
3. Albert Einstein’s theory of general relativity.
4. 1919, Arthur Eddington’s observations

The Uncertainty Principle Documentary BY BBC TWO from Published on 16 Oct 2016 Cosmic Portals

Types of Stars Song by Mr.Parr Published on 20 Aug 2012

The nearest star Proxima Centauri from

Creating the Elements - Sixty Symbols

Published on 16 Nov 2009
How do stars and supernovae create the elements. Sixty Symbols