Our Place in the Cosmosand

Introduction to Astrophysics

Jon LovedayAstronomy Centre

Department of Physics & Astronomy

Course Aims

To explain primarily at a descriptive level the contents, dimensions and history of the Universe, and our place within it. This will include a survey of the basic astronomical tools, and will seek to explain the way in which some basic physical laws can be applied in order to understand the observed phenomena.

Class organisation

Lectures Monday 9am Arts A5 Friday 9am Pev1 1A6

Workshops Friday 10am Our Place in the Cosmos: Pev1-2A2

Informal discussion, quizzes, student presentations

Intro to Astrophysics: Arundel 1B Mathematical background, problem sheets Taken by Peter Thomas

Assessment

Our Place in the Cosmos 15 minute presentation (weeks 5-10; 20%)

In-class quiz (week 10; 20%)

2000-word essay (week 10; 60%)

Introduction to Astrophysics 4 x problem sheets (10% each)

In-class quiz (week 9; 40%)

Briefing paper (week 9; 20%)

Lecturer

Jon Loveday Pev2 5A5 x 7719 J.Loveday@sussex.ac.uk Office hour: Tuesday 1.30-2.30

Web Resources

Sussex Direct has links to the official course document (click on the course code: F3095 or F3156)

Study Direct includes copies of these slides and other useful resources

Course textbooks

21st Century Astronomy by Hester et al. is very good, though expensive at £42

Introductory Astronomy by Holliday is cheaper

Other useful books you should find in the library include: Universe Freedman & Kaufmann In Quest of the Universe Kuhn & Koupelis

Student Feedback

Please feel free to stop me and ask for clarification at any time during classes if anything I have said is unclear

Feedback on any aspect of the course is welcome during the Friday seminar

Formal feedback will be requested via the Study Direct website during weeks 8-9. Please note that feedback provided in this way is completely anonymous

What is Astronomy?

Literally means “naming the stars” The earliest astronomers simply tracked the motions of the heavenly bodies

Modern astronomers use observations to help understand the Universe and our place within it via scientific reasoning

Astrology is not astronomy, but a pseudo-science

Why Astrology is not a Science

The constellations are only imaginary, not physical associations of stars

Constellations have shifted relative to our calendar due to precession of equinoxes since founding of astrology

Rigorous tests of astrological “predictions” have shown they do not work

The Scientific Method

Guided by observations, posit a theory that explains them

A good theory makes testable predictions about future observations, and thus is falsifiable

Scientific theories can never be definitively proved, they can only be ruled out by contrary observations

A theory that stands the test of time becomes generally accepted and possibly modified

Why Study Astronomy?

Early astronomers used positions of the stars to track the seasons and later as a vital navigational aid

Help understand phenomena such as tides and eclipses

Understand and appreciate even more the beauty of the night sky

Learn about the origin and fate of the Universe

Course Outline

Brief tour - scales in the Universe Historical overview Earth, Moon and Sun Orbits and Gravity Solar System Stars Galaxies The Milky Way The Universe

A brief tour

Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

Solar System

Milky Way

Milky Way as Viewed from Earth

NGC 891

Milky Way in the near-IR

NGC 4414

A cluster of galaxiesVirgo Galaxy Cluster

Infrared Universe

The Deep Universe Hubble Ultra-Deep Field

CMB Temperature Map

Scales in the Universe

Astronomical distances are commonly given in terms of light travel time, ie. distance light will travel in that time at its speed of 300,000 km/s

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Distances as light travel times - not to scale!

Prehistoric astronomy

Since prehistoric times, man has observed the changing phases of the moon during the lunar month, and the changing passage of the Sun during the year

One can understand how, as well as indicating the change of the seasons, man might well have thought of the stars as causing the change

Hence religious significance of the heavenly bodies, and birth of astrology

Dots below horses thought to represent changing phasesof the Moon

Earliest depictions of the skies are found in the Cave paintings in Lascaux, SW France (c15,000 BC)

The Great Bull: An Ice Age Star Map?

Pleiades

Hyades

Orion

Prehistoric astronomy

Observations of the changing passage of the Sun and the star patterns in the night sky enabled tracking of the seasons, and hence the best times to plant and harvest crops

Observations of the Moon’s phase allowed fishermen to predict the tides

Observatories were built to track the positions of the heavenly bodies, most famously Stonehenge, 3000-1500 BC

Stonehenge

An early astronomical calculator? On summer solstice, Sun rises exactly above the Heelstone

In Stonehenge Decoded (1965), Gerald Hawkins claimed large number of alignments with Lunar and Solar phenomena, and hence that eclipses could be predicted

These claims are still controversial

At sunset close to the spring and autumn equinoxes, shadows give the effect of a snake slithering down the stairway.

El Castillo, Chichen Itza (Mayan, c1000 AD)

The Planets

It must have been noticed very early that some bodies moved faster in the night sky than the surrounding stars.

The word "planet" comes from the Greek word "planetes," which means "nomad” or “wanderer”.

To the Babylonians and Sumerians before them, the planets were "stray sheep”.

The Ancient Greeks

By far the most famous early astronomers are the ancient Greeks. Between about 500BC and 100BC, they built a picture of the Universe which dominated for over 1000 years.

Thales (624 - 545 BC)

Realised that celestial objects were at different distances, that the Earth was spherical, and that the light of the moon was reflected sunlight.Pythagoras (582 - 500 BC)

Produced the first geocentric model of the Universe, with everything making perfectly circular orbits around the Earth.

Geocentric Model