Homework #1 will be posted on the class website by tomorrow afternoon Homework #1 will be posted on the class website by tomorrow afternoon. An announcement will be sent via email.

Which of the following best describes what we mean by the “universe”? (red) A vast collection of stars that number as many as the grains of sand on all the beaches on Earth. (blue) All the galaxies in all the superclusters. (yellow) The universe is another name for our Milky Way Galaxy (green) The sum total of all matter and energy.

Which of the following best describes what we mean by the “universe”? (red) A vast collection of stars that number as many as the grains of sand on all the beaches on Earth. (blue) All the galaxies in all the superclusters. (orange) The universe is another name for our Milky Way Galaxy (green) The sum total of all matter and energy.

Which of the following has your "cosmic address" in the correct order? You, Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe You, Earth, Local Group, Local Supercluster, solar system, Milky Way Galaxy, universe You, Earth, solar system, Local Group, Local Supercluster, Milky Way Galaxy, universe You, Earth, solar system, Local Group, Milky Way Galaxy, Local Supercluster, universe

Which of the following has your "cosmic address" in the correct order? You, Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe You, Earth, Local Group, Local Supercluster, solar system, Milky Way Galaxy, universe You, Earth, solar system, Local Group, Local Supercluster, Milky Way Galaxy, universe You, Earth, solar system, Local Group, Milky Way Galaxy, Local Supercluster, universe

Working in scientific notation Math review Working in scientific notation

Working in scientific notation 10n x 10m= 10n+m 0.0032 = 3.2 x 10-3 10n / 10m = 10n x (1/10m) = 10n x 10-m = 10n-m ____________________________________________________

Working in scientific notation 10n x 10m= 10n+m 0.0032 = 3.2 x 10-3 10n / 10m = 10n x (1/10m) = 10n x 10-m = 10n-m ____________________________________________________ 2,325,000,000 x 62,000,000,000 = = 2.325 x 109 x 6.2 x 1010 = 2.325 x 6.2 x 1019

Working in scientific notation 10n x 10m= 10n+m 0.0032 = 3.2 x 10-3 10n / 10m = 10n x (1/10m) = 10n x 10-m = 10n-m ____________________________________________________ 2,325,000,000 x 62,000,000,000 = = 2.325 x 109 x 6.2 x 1010 = 2.325 x 6.2 x 1019 2,325,000,000 x 6,250 x 0.0033 / 714,000,000,000 = = 2.325 x 109 x 6.2 x 103 x 3.3 x 10-3 / 7.14 x 1011 = = (2.325 x 6.2 x 3.3 / 7.14) x 109+3-3-11 = 6.66 x 10-2

Science begins with observation: Understanding the visible sky

Looking for patterns

The Ancient Roots of Science Many cultures throughout the world practiced astronomy. They made careful observations of the sky – they were very familiar with the sky Over a period of time, they would notice cyclic motions of: Sun Moon planets celestial sphere (stars)

The origins of astronomy and the physical sciences stem from: observing the sky and nature finding repeatable patterns seeking natural explanations for these patterns

With the naked eye, we can see more than 2,000 stars as well as the Milky Way. While stars move around the sky, they remain “fixed” relative to each other. Other objects (e.g., Sun, Moon, planets, comets) move relative to the stars.

The Sun moves east to west, full circuit around the sky, each “day” Relative to the stars, the Sun moves slowly eastward each day (~ 1 degree/day): full circuit around Celestial Sphere in one “year” Path of Sun on Celestial Sphere is called the “Ecliptic” Constellations the Ecliptic passes through are referred to as the “zodiac”

Planets Known in Ancient Times Mercury: difficult to see; always close to Sun in sky Venus: very bright when visible; always close to Sun in sky, but can be father than Mercury Mars: noticeably red Jupiter: very bright Saturn: moderately bright

The daily paths of stars appears to move in a circular manner about a fixed point in the sky. Stars that are particularly close to this point never move below the horizon (“circumpolar stars”)

Planets are always seen close to the “ecliptic”

Motions of the planets On short term (diurnal motion), planets appear to move with the stars, east to west, making a full circuit around the sky (meridian to meridian) in approximately one day Most of the time, planets move slowly eastward each day relative to the stars: different planets at different rates

Some planets occasionally reverse their motion relative to the stars for a few days (“apparent retrograde motion”).

Useful tool for understanding the sky: www.stellarium.org

Patterns observed in sky (partial list) Stars rise in east, set in west Sun rises in east, sets in west Planets rise in east, set in west Moon rises in east, sets in west Sun moves ~ 1 degree/day eastward relative to stars. Rising/setting points of Sun cyclically move north and south during year Sun repeats its path through stars each year (Ecliptic) Planets always found near the Ecliptic Planets usually move eastward relative to stars Some planets occasionally reverse this motion Mercury and Venus (inferior planets) are always close to the Sun in sky Superior planets (Mars, Jupiter & Saturn) can appear anywhere along the Ecliptic relative to the Sun.

Understanding and explaining motions observed in sky led to geometric models for the geometry of the universe. These models, in turn, motivated the development of the physical sciences: required to explain this geometry.

It did a reasonably good job explaining these motions. What causes the observed motions of the stars, sun, moon, and planets in the sky? The Greeks developed a model for the Universe that lasted for nearly 15 centuries. It did a reasonably good job explaining these motions.

Claudius Ptolemy (100-170 CE) Developed a “geocentric” model of the universe designed to fit the observational data. Ptolemy and later scientists were strongly influenced by the belief of Plato that … “all natural motion is circular”

Although the geocentric model of Ptolemy gained dominance, Aristarchus of Samos actually proposed that the earth rotated daily and revolved around the sun

Ptolemy’s Geocentric Model Earth is at center (Geocentric) Sun orbits Earth Planets orbit on small circles (epicycles) whose centers orbit the Earth on larger circles (this explains retrograde motion)

Apparent retrograde motion in geocentric model

Planet orbits lie in approximately the same plane (this explains why the planets are always near the ecliptic) Inferior planet epicycles were fixed to the Earth-Sun line (this explained why Mercury & Venus never stray far from the Sun). Geocentric Model

Ptolemy’s Geocentric Model Relied upon circles upon circles (epicycles & defferents) to explain the motions of planets and the sun. Tied to Plato’s belief that “all natural motion is circular” With modifications (e.g., additions of epicycles upon epicycles), remained the standard through the middle-ages.

Problem: In order to track the observed motions of the planets with reasonable accuracy, Ptolemy and others had to introduce many complications to the simple epicyclic picture: This violated the aesthetic sensibilities of everybody (including Ptolemy himself).

made fairly accurate predictions, but was horribly contrived! Ptolemy’s model, with modifications, fit the data & made fairly accurate predictions, but was horribly contrived!

“If I had been present at the creation, I would have recommended a simpler design for the universe”. - Spanish monarch Alphonso X (13th century)