Physics 306 (Basic Astronomy)
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Physics 306 (Basic Astronomy) Fall 2006 Instructor: Dr. Alexey Belyanin (979) 845-7785, Room ENPH 509 Email: [email protected] Office Hours -- 12:45-14:45 TTR, or by appointment

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Physics 306 (Basic Astronomy)

Fall 2006

Instructor: Dr. Alexey Belyanin

(979) 845-7785, Room ENPH 509

Email: [email protected]

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).

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Homework: 10% of the grade

Use WebAssign to receive and submit assignments:

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3 mid-term exams: 20% of the final grade each

Final exam: 30% of the final grade

Homework: 10% of the grade

Use WebAssign to receive and submit assignments:

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!

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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.

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

Mars Climate Orbiter 1999

Remember and check UNITS

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

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

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

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From the Fall 2005 material as compared to the textbook

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Why astronomy is fun material as compared to the textbook

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

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Structure of the course material as compared to the textbook

  • Scale and structure of the Universe

  • The night sky

  • History of astronomy

  • Celestial mechanics

  • Astronomical tools

  • The Sun

  • Birth, life, and death of stars

  • Galaxies

  • Cosmology

  • The Solar System

  • Life in the Universe

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Chapter 1: setting the stage material as compared to the textbook

Our place in the Universe

Scales and distances

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Milky Way Galaxy material as compared to the textbook

25,000 light years,

Or ~ 8 kpc, or 2.5x1017 km

200 billion stars

Galactic year = 225 million yr

Our sun is 4.6 billion yr old

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Hubble Deep Field Earth

10 day exposure photo!

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

1011 galaxies in the observable universe

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

Space observations as a time machine

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10 Earth7 m

Earth radius = 6378.164 km

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109 m

Radius of Moon’s orbit = 384000 km

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1011 m

1 Astronomical Unit = 1.51011 m

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1013 m

Mean radius of Pluto’s orbit = 40 AU

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

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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.

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2003 UB313 “Xena”: the largest dwarf planet so far planets

R = 2400 +- 100 km – larger than Pluto!

Pluto: R = 1185 km

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Voyagers 1 and 2 planets

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

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The Oort Cloud – source of long-period comets planets

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.

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planets 102

1017 m

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Proxima Centauri (Alpha Centauri C) planets

Distance to  Cen C = 4.2 ly = 1.3 pc = 41016 m

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Need to introduce new units of distance planets

1 light-year (ly)  1016 m

1 ly = c1 year (the distance the light travels in 1 year)

Velocity of light in vacuum c = 3 108 m/s

1 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

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Huge isolation of stars: planets

Distance between stars

= 107

Star diameter

The time needed to reach Proxima with modern spacecrafts:

Looking through space = travel in time!

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planets 102

1019 m

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Local Bubble planets

Density ~ 0.05 atoms/cm3

Temperature ~ 105 K

Remnant of supernova


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Milky Way Galaxy planets


1021 m


100 billion stars

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planets 102

1023 m

Neighboring galaxies: Mpc scale

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Groups planets



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planets 102

1025 m

500 Mpc scale

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10 planets 17 m

= 3 pc




107 m


109 m


1011 m

= 1 AU

Solar System

1021 m

= 10 kpc


1025 m

= 100 Mpc



1026 m

= Gpc



Distance scale

Looking through space = travel in time!

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Contents of the Universe planets

  • 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