One purpose of a liberal arts education is to make your head a more interesting place to live inside of for the rest of your life.

President McPherson, Bryn Mawr College

PhilosophyKnowledge, and understanding, are wild things, to

be hunted down and subdued.

Ignorance, stupidity and superstition are infectious, treatable conditions;

but their successful treatment requires the cooperation of the patient.

Introduction Books Syllabus Other stuff you’ll need

What is Astronomy? Oldest “science” dating back to ~4000 B.C. First of sciences to be quantitative Unusually appealing since it’s often

observational and outside Modern astronomy is primarily astrophysics

Study of laws guiding celestial phenomena Study of theories which explain celestial

phenomena

Astronomy is not, repeat… not ASTROLOGY Astrology is an ancient religion Results of many studies:

No evidence exists that astrology has any predictive power at any statistical level of confidence. Period.

But… the records of ancient astrologers have been useful for studying paleoastronomy

What Astronomy Isn’t

Every day Sun moves from east to west

Every night Stars move from east to west

When it can be seen, Moon moves east to west… Slightly slower than the stars

Some Basic Observations from a Geocentric (Homocentric) P.O.V.

About every month (~28 days) Moon cycles from new to full to new Moon moves ~1 h (15°) east every 24 h Which means it rises ~1 h earlier every day

Every night A constellation sets ~4 min earlier

Therefore the sun appears to move from one zodiacal constellation to another

Every 12 months The same constellation will be in the south

Some Basic Observations from a Geocentric (Homocentric) P.O.V.

The Zodiac Sun moves along a path through a specific

group of constellations Path = ecliptic Aries, Taurus, Gemini, Cancer, Leo,

Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces

Every now and then a bright “star” wanders along the ecliptic, gradually moving east, but generally following the stars’ nightly motion.

Some Basic Observations from a Geocentric (Homocentric) P.O.V.

The Ecliptic Constellations

As we proceed through the course, we will jump back and forth through time.

We will start with modern thought then take a historical view and work our way back to the 20th century (and beyond).

But first….

The Persistence of Memory, S. Dali

Some Important Definitions Astronomical Unit, AU

Distance of 1.5 x 108 km (93 million miles)

c = s.o.l. Cosmic speed limit: 3.00 x 108 m/s, 186,000 mi/s

Distance can be measured by the amount of time the light traveled from an object. Recall d = r x t

Some More Important Definitions Light year, ly

Distance light travels in 1 yr 9.461 x 1012 km (that’s 9.5 trillion km to you and me)

That’s… 9,461,000,000,000 km 5.879 x 1012 mi (5.9 trillion miles!)

Parsec, pc Parallax-second (but that’s not important now)

3.26 ly

A Short History of the Universe

Galaxies: Hubble Space telescope image

Edwin Hubble, who started out as a lazy, rich kid, became one of the most important of all astronomers.

Hubble (1921)

Galaxies move away from us at a speed proportional to their distance

Hubble’s Discovery of Expansion

Gravitational Collapse

Regions with more particles (higher density) become gas clouds

Gas clouds become stars and galaxies Galaxies congregate together in filaments,

groups and clusters

But we are inside one of these galaxies, so all we see are the nearby stars. We can see other galaxies if we use a telescope

The Cosmic Microwave Background

Still, limited evidence for a Big Bang. Gamow and Peebles predicted that there should be a “glow” left over from this huge, hot expansion in the microwave region of EM radiation.

Objects and even “empty” space give off a characteristic spectrum of electromagnetic radiation depending on their temperature: called “blackbody” radiation. You glow in the infrared.

Gamow calculated that if the temperature then was 20,000 degrees; today it would be about 6 degrees.

… by Penzias and Wilson, two physicists from the Bell labs, who got the Nobel prize in 1978

In 1964, the radiation predicted by Gamowwas finally detected, with this antenna …

antenna

Penzias

Wilson

In fact, the snow that one can see on an untuned TV is also due in part to that radiation emitted by the Universe as it was just 380,000 years old !

COBE Fluctuations

Gamow was wrong. It’s not 6 K, but ~2.7 K. This means the universe is older than he predicted.

Wilson Microwave Anisotropy Probe

In 1992, the COBE satelite (Cosmic Background explorer)gave the first image of the radiation

Before correction of the Earthmovement around the Sun

The final image of the microwaveRadiation

Before correction of the microwaveradiation emitted by our own galaxy

The CMBR and the Copernican PrincipleThe Copernican Principle: The universe should appear the same regardless of the location of the observer

Just how homogeneous and isotropic is the universe? Reasonably so for galaxies on scales of 100’s of millions of light years.

What about the CMBR? -- the temperature is the same to a part in 10,000 in every direction in the sky!

Small variations only observed in 1993. Now studied with great precision.

Results of detailed nucleosynthesis calculations:

The fraction of the universe made of Baryons = protons + neutrons

More support for BB Cosmology

Helium Abundance in the Universe At the late time (as we shall see) of 3

minutes in the history of the universe, atomic nuclei were created.

Big Bang theory predicts that the relative abundances of hydrogen and helium were:

Hydrogen 76% Helium 24% Lithium 1 part per 1010

• Due to nuclear fusion in stars since the Big Bang, current abundances:

– Hydrogen 73%– Helium 26%– Everything else 1%

More support for BB Cosmology:

COMPOSITION OF THE UNIVERSE

If 5% of the universe is baryons, what is the rest?

From studies of CMBR, of distant supernova explosions, and from Hubble and ground-based observations we know:

5% baryons (protons, neutrons) 35% dark matter (zero pressure) 65% dark energy (negative pressure)

A Confusing Picture: Where Do We Stand?

We have a good understanding of the history of the universe, both from observations and well understood theory, from t = 180 seconds.

BUT: We don’t know why there are baryons at all! We don’t know what constitutes 95% of the

energy/matter of the universe. We know that the universe underwent a

period of inflation. But we have little idea what inflation is.

A Confusing Picture: Where Do We Stand?

To answer these questions, we need to know how the universe behaved when the temperature was extremely high. Temperature equates to energy. So we need to know about high energies.

Experiments at higher energy accelerators at CERN (Geneva) and Fermilab (Chicago) are testing our understanding at extremely high energy.

What do we know?

Particle physicists know the laws of nature on scales down to one-thousandth the size of an atomic nucleus. The ``Standard Model”. This corresponds to temperatures about 1,000,000 times those of nucleosynthesis.

BUT THIS IS NOT ENOUGH TO ANSWER OUR QUESTIONS

Experiments at higher energy accelerators at CERN (Geneva) and Fermilab (Chicago) are testing our understanding at even shorter distances. Expect to discover new phenomena.

PDG Wall Chart

Summary of Cosmologic Measurements The Big Bang theory is consistent with

observations. Specifically

Hubble Telescope can view the universe ~1,000,000,000 years after the Big Bang

The COBE satellite can view the universe ~300,000 years after the Big Bang

The Hydrogen/Helium ratio can view the universe ~3 minutes after the Big Bang