Essential information:

Lecturers:

Prof. Deane Peterson Office: ESS 454 Tel: 632 – 8223 e-mail: deane.peterson @ sunysb.edu Office Hours: Tues. 11:10 AM – 12:10 PM Wed. 11:30 AM – 12:30 PM

Prof. Paul Grannis Office: Graduate Physics P101

(in Main Physics & Astronomy office) Tel: 632 – 8088 e-mail: paul.grannis @ sunysb.edu Office Hours: Mon. 2:00 – 3:00 PM Wed. 3:00 – 4:00 PM

TAs: Jinmi Yoon (AST 101 grading) Daniel Kerr (AST 112 lab)

Astronomy 101 – Spring 2003

Lecture 1 Jan. 22, 2002

Course web page:

http://www.astro.sunysb.edu/dpeterso/AST101/index.htmlhttp://www.astro.sunysb.edu/dpeterso/AST101/index.html

Contains course info, homework, lecture notes, grading policies, observing projects, links to other sites etc. Look for course news here.

Text: Astronomy Today Chaisson & McMillan. We will cover

Chapters 1-4; a little material on the solar system (Ch. 6 – 15); and Chapters 16 – 27. Lecture plan on web and in handout.

Course structure:2 Lectures per week (Mon, Wed) and a 1 hour recitation.

Lectures introduce the material. There are assigned questions and problems from the book (see web page or handout). See also questions for thought in Lecture.

Recitations review assigned questions and treat some topics in more detail. There will be about 5-6 quizzes in Recitation based on homework. The best 3 quiz grades will be used as a component of recitation grade.

There are 3 observing activities required. Two require observations over the full semester (start now!)

Prerequisites:No formal prerequisites other than high school algebra and

some acquaintance with high school chemistry. Algebra will be used in describing astronomy and physics concepts in lecture and recitation.

Exams:2 Midterm exams (in lecture hour on Feb. 26 and Apr. 7) and

one Final Exam (cumulative) on May 19, 8AM. There will be no makeups for a missed Midterm; those students with a valid excuse will have the average of the remaining midterm and final used for the missed exam.Medical excuse must be signed by Doctor with a phone number indicated and must specify the nature of the illness. Infirmary notes indicating only that a student has visited are not accepted (you may ask the infirmary for the doctor’s note, or get one from a private physician).

Grading:15 points for each Midterm30 points for Final30 points for recitation (Quiz average and Instructor

evaluation)10 points for the observing projects

Disabled policy:If anyone has a condition which will make it difficult to carry

out the work, or which will require extra time on exams should see the lecturers in the first week of class, or visit the Disabled Student Service.

Academic honesty:

All work that you hand in must be your own! Copying from others, use of reference materials on quizzes or exams, fabricating data on the activity projects will result in zero for that work and will be reported to the College Committee on Academic Honesty.

Our role in this course:

Our job is to prepare clear lecture and recitation presentations, and to give you all the information you need about the course. We will make ourselves available for your questions, and will treat students with respect.

Your role in this course:This is your education! You will gain in proportion to the effort that you put in. Much of what you retain from a course like this will be how to think about the universe we live in. Try to focus on how things work and how we know what we do – more than the specific facts, for this is what you will remember.

Astronomy, like all science, is based on observation and experiment; if we do not observe it, we don’t know it! In the case of astronomy, YOU can see many of the phenomena simply by looking at the sky! Get into the habit of looking at the sky.

We do not expect you to understand everything that we describe on the first pass – your job is to ask questions if you don’t understand so we can try again with a different approach. You have to participate in the learning process!

Come see the faculty in this course with your questions – this is an essential part of your learning experience.

Astronomical distance scales vary widely. We use different units for talking about solar system, our galaxy, the universe at large:

Planet earth: diameter ~ 15,000 km

1 km = 1000 m (1 km = 0.62 miles)

Star (our sun): diameter ~ 1,500,000 km (100 times larger than Earth)

Distance from Earth to Sun = 150,000,000 km = 1 ASTRONOMICAL UNIT (AU)

Units matter! 10cm, 10m, 10km, 10AU are very different! Numbers without units are meaningless.

Astronomical Distances

150,000,000. = 1.5 x 108

8 7 6 5 4 3 2 1

Shift decimal point 8 places to left and get factor 108

Large numbers: Scientific notation for 1AU expressed in km:

1 AU = 150,000,000 km = 1.5 x 108 km

Examples: 1000 = 103 ; 1,000,000 (1 million) = 106

Small numbers: 1 km expressed in AU is

1 km = (1/150,000,000)AU = 0.000 000 0067 AU = 6.7 x 10-9

AU

0.000 000 0067 = 6.7 x 10-9

Writing out very big and very small numbers is a pain! Use scientific notation.

Shift decimal point 9 places right to get factor 10-9 1 2 3 4 5 6 7 8 9

Examples: 0.001 = 10-3 ; 0.000 0001 (1 millionth) = 10-6

Write diameter of earth (6,378,000 m) and size of atom (0.000 000 015 cm) in scientific notation.

Our galaxy (Milky Way) diameter = 1018 km = 6.7 x 109 AU across. -- so big we use a new unit LIGHT YEAR (ly). 1 ly is distance that light travels in 1 year at speed of light = 3 x 105 km/s. There are 3.16 x 107 seconds in a year, so

1 ly = (3 x 105 km/s) x (3.16 x 107 s) = 3 x 3.16 x 105+7 = 9.46 x 1012 km

Milky Way is about 100,000 ly = 105 ly across.

Cluster of galaxies is ~ 1 x 106 ly across

( rate x time )

Entire observable universe is about 15 billion ly (1.5 x 109 ly)

What is the size of the universe in km?

We observe objects on the sky as if pasted on CELESTIAL SPHERE. But objects that look close to each other may be at vastly different distances along our line of sight.

Constellation ORION (the hunter) is a collection of stars that are at quite different distances.

The familiar constellations group stars that are typically very far apart and quite unrelated

Find Orion high in the sky at 10 PM

Determine positions on the sky in ANGULAR MEASURE

1 full circle on sky = 360 degrees (O)

Each 1O has 60 arc minutes (60’)

Each 1’ has 60 arc seconds (60’’)

(arc minutes and arc seconds have nothing to do with time units !)

20O

Orion is ~ 20O

across

Moon’s diameter subtends an angle of about 0.5O = 30’

30’

Scientists measure angles in Radians

2 radians make a full circle (360O)

Thus 360O = 2 radians (1 radian = 57.2O)

Angle in radians = Angle in degrees x (2/ 360)

Angular size and real size (in meters, km, AU, ly etc) are related. We must know the distance to the object to relate them.

d1

S1d2

S2

Object 1 with size S1 at distance d1 has same angular size as object 2 with size S2 = 2S1 at distance d2 = 2d1 Simple ratio for objects of equal angular size:

S1/S2 = d1/d2

Relationship of angle and size: S = d

(if in radians, and small – less than about 0.1 radians or 6O)

What is the angle subtended by a penny (diameter = 2cm) held at a distance of 4 m (400 cm) from your eye? (in radians and in degrees)

What is the difference in the angle from your left and right eyes to a point on the wall that is 10 m away?

Sky coordinates:

The earth REVOLVES around the sun in 1 year in a nearly circular orbit. (To us it looks like the sun orbits the earth – and the ancients thought this to be the case). The line traced by the sun on the celestial sphere is the ECLIPTIC. Each one-twelfth of the ecliptic (360O /12 = 30O) is one of the signs of the zodiac. Today, the Sun is entering the “house of Aquarius”

Earth location today

Does astrology (foretelling fortune by location of sun at your birth) make any scientific sense? Why or why not?

N

S

N

Spring equinox

Fall equinox

Summer in NY sun high in sky; more than ½ day in sunshine

Winter in NY; sun low in sky; more than ½ day in night

In addition to the Earth’s revolution around the sun, it ROTATES on its axis from N to S poles in one day.

The axis of rotation is inclined at 23.5O with respect to the axis of revolution. The intersection of the line from Earth center through N or S pole with celestial sphere are the Celestial poles. The projection of the earth’s equator (the plane perpendicular to the polar axis) is the Celestial Equator.

1 3

overhead

ove

rhead

Planes of celestial equator and the ecliptic intersect at EQUINOXES. Happens at points in orbit on ~Mar. 21 and Sept. 21.

Show with a diagram why it is summer in N hemisphere when winter in S hemisphere

North celestial pole Celestial

sphere

To the ‘fixed’ stars

Time for earth to rotate to take the sun from overhead one day to overhead the next day is SOLAR DAY.

Time for earth to rotate to take the fixed stars from a given location to same location the next day is SIDEREAL DAY.

Since Earth moves 1/365th of way around its orbit in 1 day, Solar day is longer than Sidereal day. (by about 4 minutes)

What would be relation between Solar and sidereal day if Earth rotated in opposite sense to its revolution on orbit?

Lunar sidereal month is shorter than SYNODIC month (time from full moon to full moon)

What is the phase of moon today?? At what time does full moon rise? When does 1st quarter moon rise?

Moon is in approximately circular orbit around the earth – so travels in a circle whose center moves around the sun.

The moon ‘shines’ by reflected sunlight, so in 1 ‘lunar month’, the fraction of its surface seen illuminated on earth varies.

Moon in Earth’s shadow causes LUNAR eclipse – at time of full moon only. Can see lunar eclipse from anywhere on earth.

Moon’s shadow falling on Earth causes SOLAR eclipse. Solar eclipse only in limited region of moon’s shadow.

Solar eclipse

Lunar eclipse

Moon’s orbit is not exactly in the ecliptic plane. Can only get solar eclipse when Earth, Sun and Moon line up exactly, so not an eclipse every month.

No eclipses if moon is above the Earth-Sun line.

Why is a solar eclipse more rare than a lunar eclipse?