AS 101 - Mon Sep 14, 2026 - Lecture 01

Before class

• First class - nothing to prepare

In class

• Everything started with astronomy
• Milk way Galaxy, shaped like a spiral but not all galaxies are shaped like spirals
• Space, matter (material), time are interconnected - can't have 2 without the other
• Everything is constantly moving and spinning
  • Thus, your coordinates will never be the same
• Physics is considered fundamental science
  • Fundamental principles of the Universe
• "There are two seasons in Canada - Winter... and construction"
• There are many Hypotheses and theories about astronomy like maybe the universe will freeze one day
• Specific units we are using

**** DO THIS ****

• When solving a problem, we should check if the answer seems reasonable - "Reasonableness of Results"

  • You can't drive 7,000m in 5 hours

• We'll be using scientific notation

  • ${10}^{-9}=\text{ Nano}$
  • ${10}^{-10}=\text{ Nano}$ DO THIS

• Keep in mind that models are not reality

  • They help us interpret phenomenon and interact with them directly
  • They are human creations
  • Lots of times, they fail because they don't accurately represent reality
  • We either disregard failed models or improve them and figure out what went wrong
  • We don't even know what nature is - "Nature does not have an obligation to reveal itself to you"

DO THE SIGNIFICANT FIGURES

Two important units in astronomy:

• Light year (ly) is the distance travelled by light in one year (IT'S A UNIT OF DISTANCE NOT TIME)
  • $1\text{ ly }=9.46053\times {10}^{12}\text{ km}=9.46\times {10}^{15}\text{ m}$
  • Also tells you how old the light is. If a star is 4 ly's away, then the image we're seeing is from 4 years ago
• Astronomical unit (Au) is the AVERAGE distance between the earth and the sun (ANOTHRE UNIT OF DISTANCE)
  • Fun fact: Your age is the amount of times you've gone around the sun
  • Not the actual distance because the distance between the Earth and sun is not a constant number, so you take the average between the furthest an shortest distance.
  • Light from the sun takes 500 seconds (or 8 minutes 20 seconds) to reach our eyes here on earth
    Lecture notes

After class

• Redo the in-class MyLS quiz if you want the practice (marks were for voting in class)