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Midterm

Astronomy 2022A/B Study Guide - Midterm Guide: Social Animal, Intracluster Medium, Nucleosynthesis


Department
Astronomy
Course Code
ASTR 2022A/B
Professor
Chris Racknor
Study Guide
Midterm

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Midterm Notes Astronomy 2022a
Lecture 0
Creation Stories
Genesis- God created Heavens and Earth in seven days and nights. Earth was waste and void
Greco-Roman- beginning only Chaos, out of void Erebus
Nordic-Germanic- In the beginning the was only Ginnungagap, a great void
Hopi- Creator Taiowa, no time, no shape and he created finite Sotuknang
Chinese- Pangu in egg until he finnaly broke it
What is Science?
Concerted human effort to understand (or better)
o History of natural world and how the natural world works.
o With observable physical evidence as the basis of understanding
o Done through observation, or experimentation under controlled conditions
The Scientific Method (Karl Popper Science is a history of corrected mistakes)
o Observation
o Induction
o General principle
o Deduction
o Prediction
o Experiments
o Revision
Science and the Universe
Supreme being cannot be examined, thus science is powerless to answer question
o However doesn’t mean one doesn’t exist
Philosophy helps fill that void
Lecture 1 the Universe: Early Thoughts
Rough numbers
The symbol ~ means roughly equal to
o Ex. 24+32 ~10^2
What is the Universe or Cosmos?
All space, matter and energy that is accessible to us
o Cosmology being the study of the universe
Cosmogeny/genesis: birth and start
Cosmogony: infancy
Eschatology: senility or last days
Cosmothanatos: death end
Flat Earth
Was a common assumption across cultures
o Such as in Egyptian cosmology which was similar to Mesopatmaian
o Nut (Sky), Shu (Air), Geb (Earth), Nun (Water), Naunet (Abyss)
All in a flat line
However the Greek Aristotle was most famous to advocate a spherical earth
o Eratosthenes (240BC) measured Earths diameter within 2%
Shadows in columns in Egypt disappeared, meaning sun was dirtectly overhead
Thus because this didn’t happen in Alexandria, deducted that the earth was spherical
Deducted the sun was far away and its rays would shine parallel on the Earth
Thus the shadows at Alexandria would be titled in respect to Syene, Egypt
Was not enough to prove earth was a sphere, because of the assumption that the sun was far
away, Earth could still be flat if sun was close
Round Earth
Hull-down effect

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o A ship a few km off-shore will have its lower part to appear below the horizon
Was well known to ancient sailors
Most Greeks believed Aristotle
o But he incorrectly believed that the Earth was the centre of the Universe
Because if the Earth moved, there would be a howling wind
(all stars seem to spin on asingle sphere which we some from the insde?)
It is because planets(wanderer) were points of light in the sky that moved relative to the stars
Thus Aristotle’s universe required one sphere per planet, to explain what was being
seen
Planets
The naked eye can see 5 planets: Mercury, Venus, Mars, Jupiter and Saturn
o The constellation the sun rises or sets in on your birthday determines your astrological sign
o The moons motions against the stars is fastest and easiest to see
Moves its own width every hour
Over days and weeks the planets can be seen relative to the stars
o Their motion is confined to a band of twelve constellations, the Zodiac
Ptolemy (85-165 AD)
Claudius Ptolemaus, believed Aristotle geocentric model, but improved it
Accounted for the fact that planets sometimes appear to backwards
o Retrograde motion
Some people tried to explain it by sudden stops and reverses but didn’t seem likely
Suggested that planets move in small circles (epicycles) while it orbited the earth
Was widely believed for 1500 years
o Was clunky and problematic
Only gave good predictions for a few years or decades
Thus predictions had many errors by circa 1400 AD
o King Alfonso X God should of recommended something simpler
Copernican Theory
Polish monk, proposed a heliocentric model
o Pros
Was simpler, and explained why the inner planets never travel far from the Sun
Reproduced much better the observed changes in brightness of planets
Natural reason for the seasons
No epicycles for retrograde motion
o Cons
Could not predict the positions of planets any better (unless you added epicycles
Did not explain why no wind was head
New the earth would have to go at least 100,000 per hour
Was no longer philosophically in the center
Ugly things were on the ground the center, where as great things were in the air
o But now the earth was circling and in the realm of good
Because we should sit on the bottom of universe
The fall of the Ptolemaic system
Tycho Brahe saw supernova in 1572
o Undermined the idea that the stars were perfect ad unchanging in the Ptolemaic systems
Galileo made a spyglass in 1609
o Found 4 moons circling Jupiter
Again undermining the idea that things orbited because they avoided the Earth, why would
moons be orbiting the pure Jupiter
o Ended up in hot water because of his advocacy for heliocentric models
o The church was strongly opposed to this because
First university was founded to teach church law

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The church kept much of Greek teaching and early scientists were largely church men
Vatican observatories date back to 1582
o However Copernicus (heliocentric Godfather) was a monk and his book of theory was dedicated to Pope
Paul III
So why did Galileo really get in trouble?
Galileo had already met Pope Urban VIII, and was till permitted hypothetical discussion
of the heliocentric theory, as long as it was stated to be true
o Even had papers with the crest of the Pope
Was also personally given permsiion by the new pope to discuss the
heliocentric theory
But Galileo published Dialogues Concerning Two Chied World Systems
o Conversation between Salviati, Sagredo and Simplicio
Simplicio is made out to be a fool to defend geocentric
Using Barberini (Pope Urban) argument
o Thus was placed under house arrest and recant his views
Fall of Ptolemaic System
Johannes Kepler
o From Germany and improved on Copernicuss theory by introducing slightly eccentric ellipses instead of
perfect circles
o Reproduced observation of the planets with accuracy
o Was a blow to geocentric because required ellipses to be around the sun
Isaac Newton introduced the concept of all bodies exerting gravity proportional to their mass
o Predicted elliptical orbits that matched well with Kepler
o His laws of motion explained how Earth can move with no wind.
o Thus heliocentric wins.
What of the Stars
Are stars bodies of ordinary matter to?
o Seemed unlikely because telescope revealed features on planets but just brightness for stars
o Since earth moved around sun, stars should undergo a motion called parallax
Parallax
A surveryors method of measuring distance
o Because stars appear slightly shifted different positions of Earths orbit we can determine their distance
o GET THE SLIDE shows better
o The farther away the star (d=distance in parsecs) the smaller the parallax angle p
Was only way of measuring for early scientists
o As early as 1672, Cassini for distance of Mars
o However stars were hard to determine, thus meaning that they w
Parallax is measured in arcseconds
o 1 arcsecond of movement= one parsec away
1 PARSEC equals 3.26 lighyears
1 year of light travel = 9 x 10^12 km
A circle as 360 degrees
1 degree=60 minutes of arc thus an arcminute
1 arcminute= 60 seconds of arc thus an arcsecond
1 arcsecond= 1/1296000 of a circle, thus really small
d=1/p
Stellar Parallax
1838 by Fredrich Bessel revealing star 61 Cygni, putting it 3.15 parsecs or 10.3 lightyears
o Was a parallax of 0.0000872 degrees
o Was later revealed to one of our closest stars
Distribution of stars
The initial assumption was stars were uniformly spread
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