ASTRO 2021 A|B (The Search for Life In The
Universe) Complete Midterm 1 Notes University
of West Ontario.
, lOMoAR cPSD| 19857451
Astronomy 2021A Complete Lecture Note
Unit 1
Part 1: Idealism
Idealism: A view that the true nature of reality is contained in reason and consciousness,
transcending physical reality, only mental states are knowable, the implication being a
recognition that we are not objectively seeing anything, since we know these things only
through the filter of our mind, we don’t see the world, we see what our minds can make out of
the world – Immanuel Kant, 1780’s
Part 2: The relative size of space, its vast expanse
Diameter of Earth: Can we appreciate how large the earths diameter is, it’s is 10^7 kilometers
long and is a sphere, so large we never notice its curve unless we reach elevated heights
Distance to Moon: 10^8.3 Too small to be a standard distance in astronomical discussions, it is
however, just a bit more than 1 light second away from the earth.
Distance to the Sun: Bit more than 10^11, this is the standard astronomical unit AU, we use
AUs to describe distances between objects in space. Again we use this distance because it is big
enough to be useful in descriptions of the special relationships between things in space, but still
familiar o us as a meaningful distance in our lives. 8 light minutes to get to sun from earth. Not
useful for star to star distances.
Distance to Alpha Centaury: 9 years for light to get there, about 10^16.5 meters away
Distance to Andromeda: Closest galaxy to us (closest large galaxy) 2.2 million light years away,
more than 10^22 meters.
Maximum visible distance: A little more than 10^26
There is a qualitative difference between a distance of one meter and 10^26 meters.
Part 3: In the Beginning, God Created … The Earth
Biblical Narrative: Doesn’t say when the beginning is but establishes that there was a
beginning, time does not go from eternity to eternity.
Challenges to Darwin: Darwin faced severe criticism when he released his theories, most
credibly from lord kelvin who estimated the earths age at 400 million years. His calculation
assumed that the earth originated as molten rock (proto-Earth) at a uniform temperature, 3000
degrees Celsius. Also, that the temperature beneath the surface of the earth today increases by
0.03 K/m (kelvin?) 1 degree for every 30 meters down
, lOMoAR cPSD| 19857451
This theory is completely wrong, there was no true scientific basis to this.
L = Lamda
deltaT = change in temperature
Not sure about this section!!!!!!
Part 4: Kelvin Revises His Theory
Looking Towards the Sun: Kelvin supposed the “hellions” are people living on the sun and they
burn everything on it, as a result the sun shines bright in the sky. Kelvin did not believe this.
Not his theory. He said: the best way to generate energy, gravity things falling. Kelvin says the
sun was much bigger to begin with, and as it collapses under its own gravity it releases that
energy I the form of light. The problem: How big was the sun when it started? Solution: there is
a definite limit of the suns potential size according to kelvin. Based on the inner most planet
being mercury – Sun at time = 0 would have been big enough to reach all the way to mercury
(just outside wouldn’t get sucked in). Comparing that size to what the sun is now, we can
deduce the energy release over time and get an age of the sun. = 20 million years old, new
correction to the law we used to describe the age of the earth. Destroys Darwin’s reputation,
and Darwin never recovers academically.
Rutherford working at McGill gives a talk on why kelvins estimate of the age of the earth is
completely wrong, because he thought the earth was hottest at the beginning, with a linear
decline since, but there is new heat generated!! Radioactive decay, tons of it in the earth
generating heat from within.
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