Physics 306 (Basic Astronomy)  Fall 2006

Instructor: Dr. Alexey Belyanin(979) 845-7785, Room ENPH 509Email: belyanin@tamu.edu

http://faculty.physics.tamu.edu/belyanin/phys306.html

Office Hours -- 12:45-14:45 TTR, or by appointment

The textbook is Foundations of Astronomy, Ninth Edition, by Michael Seeds (Thomson Brooks/Cole, 2007).

Homework: 10% of the grade

Use WebAssign to receive and submit assignments:

http://www.webassign.net/

Evaluation

3 mid-term exams: 20% of the final grade eachFinal exam: 30% of the final grade

Homework: 10% of the gradeUse WebAssign to receive and submit assignments:http://www.webassign.net/

 If you have an excused absence for a mid-term exam, the grade for one exam can be dropped in calculating the final average. You are allowed to bring one 8.5" x 11" page with formulas (on one side) for every exam. You can bring three such pages for the final.

With this “cheat sheet” you don’t have to memorize all formulas. However, you need to understand them!

Level of math used:

You will use simple algebra and some elementary functions, such as logarithms and exponents.

Powers of 10 will occur all the time, so the ability to work with scientific notation is important.

I will provide you with necessary math background; however, some of you might need extra practice to refresh your middle school math.

Remember and check UNITS Remember and check UNITS for all terms in the formulas!!!for all terms in the formulas!!!

Indicate units on your formula sheet

Express all terms in correct units before plugging in the formula

Check your answer for right unit

We will use metric units. See Appendix A for definitions, tables, and other important info.

Mars Climate Orbiter 1999

Advantages of taking classes over self-study

• Fighting intrinsic laziness

• Maintaining a proper speed

• Distinguishing important topics from less important ones

• Learning supplementary materials as well

• Someone is ready to answer questions

Attendance is important. We will drop/add and rearrange some material as compared to the textbook

test 3 results vs. absences

0

20

40

60

80

100

120

140

160

0 1 2 3 4 5 6 7

absences

sco

re

From the Fall 2005

Why astronomy is fun to study and to teach

• In every lecture, we reach the frontier of human knowledge

• Crossroads of physics, chemistry, biology, philosophy, …

• Breakthrough discoveries occur every year

• All scales from elementary particles (10-15 m) to the Hubble radius (1026 m) are involved; all timescales from 10-43 s to 1010 years

• No need in sophisticated tools to do observations and make discoveries

Structure of the course

1. Scale and structure of the Universe2. The night sky3. History of astronomy4. Celestial mechanics5. Astronomical tools6. The Sun7. Birth, life, and death of stars8. Galaxies9. Cosmology10.The Solar System11. Life in the Universe

Chapter 1: setting the stage

Our place in the Universe

Scales and distances

200 billion stars

Milky Way Galaxy

25,000 light years,Or ~ 8 kpc, or 2.5x1017 km

Galactic year = 225 million yrOur sun is 4.6 billion yr old

“Milky Way” – a milky patch of stars that rings the Earth

Galactos = milk in Greek

Galileo found that the Milky Way is made up of stars

Hubble Deep Field10 day exposure photo!

Over 1500 galaxies in a spot 1/30 the diameter of the Moon

Farthest and oldest objects are 12-13 billion ly away!

Space observations as a time machine

1011 galaxies in the observable universe

107 m

Earth radius = 6378.164 km

109 m

102

Radius of Moon’s orbit = 384000 km

102

1011 m

1 Astronomical Unit = 1.51011 m

Mean radius of Pluto’s orbit = 40 AU

102

1013 m

Pluto demoted to a dwarf planet on August 24, 2006!

The Kuiper Belt – home for short-period comets and dwarf planets

Starting in 1992, astronomers have become aware of a vast population of small bodies orbiting the sun beyond Neptune. There are at least 70,000 "trans-Neptunians" with diameters larger than 100 km in the radial zone extending outwards from the orbit of Neptune (at 30 AU) to 50 AU.

1-day motion of Varuna

2003 UB313 “Xena”: the largest dwarf planet so farR = 2400 +- 100 km – larger than Pluto!

Pluto: R = 1185 km

HST image of Xena

Launched in 1977, Voyager 1 is now 100 AU from the Sun! (12 light-hours, or 15 billion km)The most distant human-made object in the Universe

Voyagers 1 and 2

The comets that are more likely to be easily visible are much rarer, and are thought to come from a great spherical cloud of cometary material surrounding the Solar System called the Oort Cloud. This sphere is a light year (50,000 A. U.) in radius, but the total mass of cometary material in this cloud is probably less than that of the Earth. Occasionally a comet in this cloud is disturbed gravitationally, for example by a passing star, and started on a long elliptical or parabolic orbit toward the Sun. These long-period comets are primarily responsible for the brighter comets observed historically.

The Oort Cloud – source of long-period comets

102

1017 m

Proxima Centauri (Alpha Centauri C)

Distance to Cen C = 4.2 ly = 1.3 pc = 41016 m

Need to introduce new units of distance

1 light-year (ly) 1016 m

1 ly = c1 year (the distance the light travels in 1 year)

Velocity of light in vacuum c = 3 108 m/s1 year 3.1 107 s

1 parsec (pc) 3.26 ly 3 1016 m

1 kpc = 1000 pc;1 Mpc = 1 million pc;1 Gpc = 1 billion pc

Huge isolation of stars:

Distance between stars

Star diameter= 107

The time needed to reach Proxima with modern spacecrafts:

yr 30,000s10m/s103

m103 124

16

Looking through space = travel in time!

102

1019 m

Local Bubble

Density ~ 0.05 atoms/cm3

Temperature ~ 105 K

Remnant of supernovaexplosion?

102

1021 m

10 kpc100 billion stars

Milky Way Galaxy

102

1023 m

Neighboring galaxies: Mpc scale

Groups clusters superclusters

102

1025 m

500 Mpc scale

107 mplanets

109 mSun

1017 m= 3 pcdistancebetweenstars

1021 m= 10 kpcgalaxy

1011 m= 1 AUSolar System

1025 m= 100 MpcLargeststructure

1026 m= GpcHubbleradius

Distance scale

Looking through space = travel in time!

Contents of the Universe

• 97% of all ordinary (baryonic) matter is in stars

• Only 3-5% of matter in the Universe is baryonic!

• 27% is cold dark matter

• 70% is dark energy

Dark matter as a gravitational lens

Remaining 70% is “dark energy”