1. Astronomy and the Universe• The scientific method• Birth, life & death of the Solar

System• Birth, life & death of the stars• Birth, life & death of the Universe• Angular measure in astronomy• Basics of powers-of-ten notation• Astronomical measures of distance• An adventure of the human mind

The Laws of Physics• A cause-and-effect Universe

– Everything in the Universe follows clear patterns– There are physical “natural laws”

• Uniform in both space & time• The common laws of physics in astronomy

– Gravity– Pressure– Electromagnetic radiation (EMR)– Spectroscopy– The Doppler effect– E = m . c2

– Strong & weak nuclear forces

The Scientific Method• Definition

– Systematically ask & answer questions• Important aspects

– Observation / experiment– Replication– Skepticism

• One common strategy– Design the experimental

procedure– Design the experimental

apparatus– Execute the experimental

procedure– Analyze the experimental

results

Hypotheses, Theories & Laws• Hypotheses

1,000’s– Educated guesses that will be modified many times– Hypothesis testing loop

• Check your predictions against experimental results• Theories

100’s– Well-tested & generally-accepted

hypotheses• Einstein’s Theory of Relativity

– “Hypotheses” are usually misnamed “theories”• When you hear “theory,” think “hypothesis” instead

• Laws10’s

– Proven & completely-accepted theories• Newton’s Law of Universal Gravitation

Scientific Evidence, Support, Proof• Evidence

– Single line of evidence• Often relatively weakaffirmation of an hypothesis

– Multiple lines of evidence• Often relatively strongaffirmation of an hypothesis

• Support– The evidence equivocally affirms the hypothesis

• This is very common in science• Proof

– The evidence unequivocally affirms the hypothesis• This is very unusual in science• ± 5.0 sigma statistical confidence

Solar System’s Birth, Life & Death• Earth: Our home planet

– Geocentric model of planetary motion• Philosophical & theological bases

– Heliocentric model of planetary motion• Observational & theoretical bases

• Our planetary system– Terrestrial & Jovian planets

• Natural & artificial satellites– Asteroids & comets

• Rocky & icy• Amazing diversity in processes & results

– Range from “solid objects” to “rubble piles”

Relative Sizes of the Sun & Planets

Diameters are to scaleDistances are not to scale

The Birth, Life & Death of Stars• Stellar birth

– Some compression mechanism begins a collapse– Gravity exceeds pressure

• Stellar life– Produce 1 helium nucleus from 4 hydrogen nuclei– Gravity & pressure in dynamic equilibrium

• Length of lifetime depends completely on mass• Stellar death

– Gravity & pressure again compete for dominance– Death processes & products depend only on mass

• White dwarf Degenerate electronpressure

• Neutron star Degenerate neutron pressure

• Black hole No kind ofpressure

Sunspots: 13 January 2013

The Birth & Life of the Universe• Birth of the Universe

– Evidence for a rapidly expanding Universe– Origins of the Universe in a Big Bang

• Origin / Creation of all matter• Origin / Creation of all energy• Origin / Creation ofspace-time

• Life of the Universe– Formation of atoms

• Initial conditions were so hot that everything was plasma– Formation of stars

• Gravitational collapse on a small scale– Formation of galaxies

• Gravitational collapse on a large scale• Destiny of the Universe

– Accelerating expansion => Universe torn apart

A Nebula Inside Our Milky Way

The Crab Nebula

A Galaxy Outside Our Milky Way

The galaxy M100

Angular Measure in Astronomy• Possible origins of 360° in a circle

– ~ 365.25 days in a year• 360 = 23 . 32 . 5

– One degree of Sun motion equals about one day• Relative to the fixed background of stars• Only ~1.5% difference from “exact” time over one year

• Variations on a theme– Degrees, minutes & seconds of arc 17° 15’

00”– Decimal degrees of arc 17.25°

• Some practical implications for astronomy– 24 hours = 360° of sky rotation– 1,440 minutes = 360° of sky rotation– 1 hour = 15° of sky rotation– 4 minutes = 1° of sky rotation

Angular Measure & the Sky

Angular Size In Astronomy• Angular distance

– Distance measured in degrees, not meters or feet– Usually measured between two points

• The position of two stars• The center of two planets

– Relatively independent of distance• Points or objects are too far away to make a difference

• Angular diameter– Diameter measured in degrees, not meters or feet– Usually measured between edges of large objects

• The left & rightedges ofthe Moon• The left & rightends ofa comet’s tail

– Extremely dependent on distance• The farther the object, the smaller its angular diameter

Angular Distance in the Big Dipper

Angular Measure & Human Hands

• Representing very small & very large numbers– Counting a large number of zeros can be difficult

• 0.000 000 000 000 000 000 000 000 000 000 000 6625 J s• 300 000 000 m / s

• The pattern– A number; a power of 10; unit(s)

• 6.625 . 10–34 J s• 3.0 . 10 8 m / s

• The rules Scientific notation– 1.000 < Number < 10.000– The exponent may be either positive or negative

• Positive: The powers of ten are in thenumerator

• Negative: The powers of ten are in thedenominator

– Appropriate units for the quantity represented

Powers-of-Ten Notation

Examples of Powers of Ten

Sizes Are Shown In Meters

Astronomical Measures of Distance• Small distances within solar

systems– Astronomical units AU Quite

close• 1.00 AU = 9.296 . 107 mi• 1.00 AU = 1.496 . 108 km

• Medium distances within galaxies– Parsecs pc Rather close

• The distance of an object with a parallax of 1.0 arcsecond– 1.00 pc = 3.09 . 1013 km– 1.00 pc = 3.26 ly

• Large distances between galaxies– Light years ly Quite far

• The distance light travels in one year– 1.00 ly = 6.324 . 10 4 AU– 1.00 ly = 9.46 . 1012 km

Parallax & the Parsec (pc)

An Adventure of the Human Mind• The scientific method

– Overwhelmingly observational– Occasionally experimental

• Discovery– Materials & processes related to

Earth• Extrasolar planets

– Materials & processes related tostars• The range of stars

– Materials & processes related togalaxies• The range of galaxies

• Pursuit of knowledge for its own sake– New & improved tools– New & improved techniques

• Scientific method– Hypothesis

• Well-educated guess– Theory

• Very often misused– Law

• Planetary motion– Geocentric model– Heliocentric model

• Angular measure– Degrees, minutes & seconds– Decimal degrees– Angular distance & angular diameter

• Powers-of-ten notation• Astronomical measures of distance

– Astronomical unit AU• Within solar systems

– Parsecs pc• Relatively close to our Solar System

– Light years ly• Very far from our Solar System

Important Concepts