ASTR178Other Worlds

Week 1, August 2A/Prof. Orsola De Marco

orsola.demarco@mq.edu.auhttp://www.physics.mq.edu.au/

current/undergraduate/units/ASTR178/

ASTR178 structure

• 7 weeks, 21 hours for the Solar System (by Orsola De Marco)

• 3 weeks on the details of the Sun and Solar System formation (by Andrei Gilchrist)

• 3 weeks on extrasolar planets (by Mark Wardle)

Assignments (25%)

• 3 assignments handed to students via website returned via collection boxes. • Content of assignments discussed in class on following Monday upon request.

Assignment Value To students deadline

1 5% 6 August 4pm 13 August 4pm

2 10% 3 September 4pm 17 September 4pm

3 10% 29 October 4pm 12 November 4pm

Practical (10%)• There is one practical posted on the website.• You can do it in your own time on any clear night between two specified dates• There is a minimum requirement of 5 observations between August 24th and September 11th• Due in on September 11• You do not need to go to the Observatory, but we will reserve two evenings for you to visit if you wish

Tutorials (15%)• Tutorials start week 2. Check what group you are in, andin which weeks and day your group goes to tutorial. Eachstudent goes to only 4 tutorial classes.• Tutorial class 1:

• Discuss the lay out of a 5 minute presentation, techniques and technology to present and topics.

• Tutorial class 2-4:• Present or listen to the presentations on a topic of your choice with relevance to this course.

Exam (50%)• Regular 3 hour exam.• Format likely some multiple choice, some short answers.

Office hours• Office Hours:

• best way to contact me: e-mail orsola.demarco@mq.edu.au• Second best, make an appointment via e-mail.• Third best come to my office right after class.• If you really must, come any time.

• READ YOUR UNI E-MAIL!!!!!!!!!!! It is the way I talk to you. Not reading your e-mail is no excuse not to have heard from me (check your unit e-mail works – did you get my test message on 30 July 2010?)

For me to know …

• Raise your hands if:

• You are a Physics of Astronomy Major• Have you taken an Astronomy course before?

A sense of place

A sense of history

A sense of heritage

The Big Picture

• Astronomy to create a sense of belonging that has a wider meaning.• Take a look at the short essay by Sandy Faber in the course book “Universe”.

Course Outline1. The Solar System in context and the celestial sphere2. Why the night sky looks the way it does. Early

observers and the scientific method.3. The terrestrial planets: Earth4. The terrestrial planets: Mercury, Venus and Mars.5. The gas giants: Jupiter, aurorae and tides.6. The gas giants: Saturn, Uranus and Neptune

and their rings.

In this class• Space and time: sizing up the Universe. The Solar System in context• Units• Angular separations and sizes• What are constellations• Earth spin, daily motion, night and day, timezones.• Earth Orbit around the Sun, yearly motion, differentstars appear overhead on different months. • The celestial sphere, north and south, the nightly motion of stars.• Latitude and longitude on Earth and how to tell Latitude by the stars

Units of the Universe (length)

• Units of the Cosmos: – Solar Radius (Ro)– The astronomical

unit (AU)– light years– parsec (=3.26 ly;

pc)– centimeter (!)

• The Scientific notation:– 1 = 100

– 10 = 101

– 100 = 102

– 100,000 = 105

– When using cm, you see a lot of, e.g., 1013!

Units of the Universe (time)

• Units of the Cosmos: – Year– Second

• The Scientific notation:– When using the second, you

see a lot of, e.g., 109 yr = 1 Gyr

Units of the Universe (mass)

• Units of the Cosmos: – Solar masses– Jupiter masses– Earth masses– Gram

• The Scientific notation:– When using the gram, you

see a lot of, e.g., 1033 gr = 1 Msun

And while we are at it …

• prefix multipliers:10 = deca100 = hecto1000 = kilo (K)1,000,000 = 106 = million = mega (M)109 = billion = giga (G)1012 = triollion = tera (T)1015 = million trillion (?) = peta (P)(exa zetta yotta)

And since we are having so much fun….

• prefix multipliers:0.1 = deci0.01 = centi0.001 = milli (m)0.000001 = 10-6 = a millionth = micro ()10-9 = a billionth = nano (n)10-12 = a triollionth = pico (p)10-15 = a millionth trillionth (?) = femto (f)(atto zepto yocto)

Another tool of the trade:angular separations

The scales of the Universe

Earth

• Radius:6357 - 6378 kmor 6.4 x 108 cm

(Concept of approximation)

Sun

• Radius696,000 kmor 6.96 x 1010 cmor 1 Ro

• ~100 x Earth

Jupiter

• Radius69,911 kmor 6.99 x 109 cmor ~0.1 Ro

• ~10 x Earth

Solar System

• Radius (Pluto)40 AU6.0 x 109 km6.0 x 1014 cm

• 40 x Earth-Sun

Our Galaxy

• Radius~15,000 pc or 15 kpc4.6 x 1022 cm

• 7.7 x 107 x SS

• LMC: 50 kpc• SMC: ~60 kpc• M31: 2.5 Mpc• Virgo Cluster: 18

Mpc

Other Galaxies

The Solar System in context

The Solar System in context

Timescales

• Supernova implosion (last phases): seconds.

• Planetary orbits: days … years … decades.

• Lifetime of the Sun: 10 billion year.• Lifetime of a 100 solar mass star: few

million years.• Age of the Universe 13.7 billion years.

Orienting yourself in the night

• The first thing you need to do in order to start understanding our place in the Universe is to look up!

The Constellations

• Stars in a constellations are not grouped in space, they are close because of chance alignment.

Constellations Names and the Zodiac

• Many constellations were named by the Greeks (including some southern ones which were more northern 2000 years ago).• Constellations names are usually Latin (e.g., Centaurus). • Stars in a constellation are called with Greek lettersaccording to their brightness ( being the brightest), followed by the constellation name in the genitive (e.g., Centauri, also abbreviated Cen).• The horoscope…

The day: The spin of Earth

The day: The spin of Earth

The year: The orbit of Earth

The night sky over the year

The night sky over the year

• The celestial sphere is an imaginary sphere centered onthe Earth, whose poles are the same as the Earth’s polesand whose equator is the projection of Earth’s equator.

The North Celestial Pole

The South Celestial Pole

• To find South at night, look for the South celestial pole and draw a line down to your horizon. That is South.

At the North Pole: how do stars move during the

night?

And at the Equator?

And where is this observer?

Latitude and Longitude

• What is the reference frame?• Latitude: equator• Longitude: the Greenwich meridian.

Measuring Latitude

• Your latitude North/South is the same as the altitude of the North/South celestialpole (easy to measure in theNorth, where Polaris marksthe spot!)

Key Ideas• Astronomy, Science, and the Nature of the Universe: The universe

is comprehensible. The scientific method is a procedure for formulating hypotheses about the universe. These are tested by observation or experimentation in order to build consistent models or theories that accurately describe phenomena in nature.

• Observations of the heavens have helped scientists discover some of the fundamental laws of physics. The laws of physics are in turn used by astronomers to interpret their observations.

• The Solar System: Exploration of the planets provides information about the origin and evolution of the solar system, as well as about the history and resources of Earth.

• Stars and Nebulae: Studying the stars and nebulae helps us learn about the origin and history of the Sun and the solar system.

• Galaxies: Observations of galaxies tell us about the origin and history of the universe.

• Angular Measure: Astronomers use angles to denote the positions and sizes of objects in the sky. The size of an angle is measured in degrees, arcminutes, and arcseconds.

• Powers-of-Ten Notation is a convenient shorthand system for writing numbers. It allows very large and very small numbers to be expressed in a compact form.

• Units of Distance: Astronomers use a variety of distance units. These include the astronomical unit (the average distance from Earth to the Sun), the light-year (the distance that light travels in one year), and the parsec.

Key Ideas

• Constellations and the Celestial Sphere: It is convenient to imagine the stars fixed to the celestial sphere with the Earth at its center.

• The surface of the celestial sphere is divided into 88 regions called constellations.

• Diurnal (Daily) Motion of the Celestial Sphere: The celestial sphere appears to rotate around the Earth once in each 24-hour period. In fact, it is actually the Earth that is rotating.

• The poles and equator of the celestial sphere are determined by extending the axis of rotation and the equatorial plane of the Earth out to the celestial sphere.

• The positions of objects on the celestial sphere are described by specifying their right ascension (in time units) and declination (in angular measure).

Key Ideas

Some sample questions and answers

What lengths are most conveniently measured in astronomical units (AU)?

A. Distances on the Earth B. Distances within the solar system C. Distances between stars in our Galaxy D. Distances between galaxies E. Only the largest distances in the universe

Q1.5

What lengths are most conveniently measured in astronomical units (AU)?

A. Distances on the Earth B. Distances within the solar system C. Distances between stars in our Galaxy D. Distances between galaxies E. Only the largest distances in the universe

A1.5

What lengths are most conveniently measured in units of nanometers (10−9 m)?

A. Distances between the planetsB. Distances between cities on EarthC. Dimensions of the human body D. Wavelengths of visible light E. Diameter of an atom

Q1.6

What lengths are most conveniently measured in units of nanometers (10−9 m)?

A. Distances between the planetsB. Distances between cities on EarthC. Dimensions of the human body D. Wavelengths of visible light E. Diameter of an atom

A1.6

What is the approximate diameter of our Galaxy, the Milky Way?

A. 50 × 106 km B. 50 astronomical units C. 50 light-years D. 50 kiloparsecs E. 10 million light-years

Q1.8

What is the approximate diameter of our Galaxy, the Milky Way?

A. 50 × 106 km B. 50 astronomical units C. 50 light-years D. 50 kiloparsecs E. 10 million light-years

Q1.8