Astronomy Part 1 General Science I Spring ‘09

History of the Universe Earth = 1 of 9 planets Sun= 1 of 100 billion stars in the Milky Way, 1 of infinite numbers in our universe

Ancient Astronomy Golden Age= 600 BC-150 AD in Greece Beliefs relied on philosophy (ideas) and observations.

Geocentric View At first, many believed the Earth was the center of the universe A geocentric view Geo=Earth -centric=center

Heliocentric view Eventually, this belief was formed into a heliocentric view. We realized the SUN was the center of our galaxy.

Modern Astronomy Ideas based more on observation Nicholas Copernicus ( , Poland) – Earth rotates – Said Earth is a planet (only 5 known at this point: Mercury, Venus, Mars, Jupiter, Saturn)

Tycho Brahe ( ), Holland Argued that if the Earth orbited the sun, then stars should appear to move over a period of 6 months. Called this the stellar parallax (the shift of an object against a background caused by a change in observer position; hard to see) Kepler was his apprentice

Johannes Kepler ( ) Laws of Planetary Motion – The path of each planet is an ellipse – Each planet travels at its own speed – Astronomical Unit (AU) = 150 million kilometers

Galileo Galilei ( ) Around at the same time as Kepler Favored the heliocentric viewpoint Created the telescope ( which later made him go blind after looking at the sun through it ) Discovered the four moons of Jupiter Saw craters on the moon

Sir Isaac Newton ( , England) Law of Gravity! Proved Kepler’s idea that planets orbit in an ellipse.

What is a star? Simply put… a big ball of gas A light year? - how far light travels in a year -300,000 km/s (kilometers a second)!

Magnitude The brightness of a star Apparent magnitude – How bright the start appears to be from Earth Absolute magnitude – How bright the star really is

Measuring Magnitude Think opposites The brightest stars have the lowest number The dimmest stars have the highest number

Hertzsprung – Russell Diagram (H-R Diagram) Came up with a way of classifying the stars Uses temperature and absolute magnitude to determine plot point on the diagram

Trip through our Universe A star is a big ball of gas. Light year= how far light travels in one year – 9.46 x meters Speed of light= 186,000 miles per second! (300,000 km/second!) Billions and billions of stars Carl Sagan 11/9/34- 10/20/96

Binary Stars Half of the stars in the sky have a companion star (a buddy) Most rotate around one another= binary star Hubble image of the Sirius (brightest star in the sky) binary system, in which Sirius B can be clearly distinguished (lower left).

Constellations Star groups that form patterns as seen from Earth Big dipper (ursa major) Little dipper (ursa minor) Orion

Nebula(e) A huge massive cloud of gas and dust. Where new stars form

How Nebulae form Gravitational forces Gravity from the sun causes gases to get closer together As the distance decreases, gravitational forces increase Forms a “protostar.” The first stage in a star’s life.

Nova When a star suddenly increases in brightness (100x) in a few hrs/days, then dims back to original state. Gases from one binary star strike the other causing nuclear explosions which we see as light. Can occur several times

Novas

Supernova Occur in stars x the size of our sun Explosions 1000x brighter than novas Temperature increases The iron core condenses and collapses from gravitational forces

Neutron Stars Occur after a supernova explosion The only thing there is neutrons. All the protons and electrons have exploded off A spoonful weighs 100 million tons on Earth!

Star Life- Cycle NebulaProtostar Main Sequence Red Giant White Dwarf Nova Super Giant Super Nova Neutron Star Black Hole Star Birth Life of a Star Death of a Star ?