Astronomy 201

The Sun and its Planets

Dr. Jeff Kriessler

Discussion

Come up with as many examples of products which are named after astronomical objects.

Discussion

Come up with as many examples of how astronomy affects your daily life as you can.

Discussion

What is a day? How would you define it to someone who doesn’t know anything about how we keep time?

TimeDay – Time it takes the Sun to return to the same position above the horizon.

Month – Time it takes the Moon to go through its phases.

Year – Time it takes to move through the seasons.

Note: Ancient definitions may differ from the modern usage!

The hour

An hour originally was the time it takes the Moon to move its own diameter against the stars.

Today we define an hour as 3,600 seconds where a second is 9,192,631,770 oscillations of a Cesium-133 atom.

“Fixed” stars and Planets

Although the stars change their positions over the course of a night and from night to night, their relative positions (their positions relative to each other) remain constant year after year.

Planet means “wanderer.” They change their positions relative to that of the fixed stars

The Planets of antiquity

SunMoonMercuryVenusMarsJupiterSaturn

The days of the Week

Sunday – the Sun’s dayMonday – The Moon’s dayTuesday – Tiw’s day – Mars Wednesday – Woden’s day – Mercury Thursday – Thor’s day – Jupiter Friday – Freia’s day – Venus Saturday – Saturn’s day

Ordering of the day names

Planets ordered by apparent length of period of revolution about a presumed stationary Earth:

SaturnJupiterMarsSunVenusMercuryMoon

Assign each planet to an hour of the day:

Saturn 1, Jupiter 2, Mars 3, Sun 4, Venus 5, Mercury 6, Moon 7, Saturn 8, Jupiter 9, …

Which planet gets assigned the 25 hour?

Discussion

Southern circumpolar stars

Total Solar eclipse

Total Lunar Eclipse

Ptolemy explanation for retrograde motion

Nicolaus Copernicus

Aristarchus explanation for retrograde motion

Tyco Brahe

Johannes Kepler

Galileo Galilei

Isaac Newton

Atom

Ceres

HST image 1995

Cassini

Ceres

Our place in the Universe

Our Address:

Case Western UniversityCleveland, OhioUSAEarthThe Solar SystemThe Milky Way GalaxyThe Local GroupThe Local SuperclusterThe visible Universe

Visible Universe

The portion of the Universe that light traveling at 186,000 miles per second, has had enough time to reach us. The visible Universe is a sphere with a radius of about 14 billion light years.

Hierarchy

Universe – made up of lots of galaxies

The Galaxies – made up of lot of solar systems

The Solar System – where the influence of the Sun dominates over the influence of other stars