1. January 10, 2006Astronomy 20101

2. January 10, 2006Astronomy 20102 What is Astronomy? The study of objects outside the Earth. Examples: The Moon What phase is the Moon in tonight? Waxing or waning? Planets, comets, asteroids Are any planets visible? Comets? The Sun and stars How do stars form and why do they shine? Do other stars have planets orbiting them? Could there be life on those planets? Lots of other stuff: galaxies, supernovae, black holes, …

3. January 10, 2006Astronomy 20103 Numbers Scientific Notation (power of ten) 1,000,000 = 10x10x10x10x10x10 = 10 6 $150,000,000,000,000 = 150x10 12 = $1.5x10 14 1 nanosecond = 0.000,000,001 seconds = 10 -9 seconds

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24. January 10, 2006Astronomy 201024 The Milky Way Sun is ~ 30000 LY from the center of our Galaxy. From our location within the galaxy, we cannot see through its far rim because the space between stars is not empty – interstellar dust or gas which absorbs visible light. The interstellar gas is the fuel for the formation of stars. Yet, interstellar material is very sparse, space between stars is quite empty – much more so than an vacuum one can achieve in the laboratory on Earth. Possibility of dark matter. Star Clusters – contain up to hundreds of thousands of stars – light years across. Star have a long life (billions of years) but not infinite – they die or collapse in spectacular ways.

25. January 10, 2006Astronomy 201025 Nearby objects (Orion Nebula in the Magellanic Cloud) Our galaxy is not unique. Many other discovered & studied. Some are close to us Magellanic clouds Most are at enormous distances. Nearest large galaxy is Andromeda, or M31.

26. January 10, 2006Astronomy 201026 M31 is part of a small cluster of over 40 galaxies one calls the local group. At distances of about 10 to 15 million LY, one finds other small galaxy groups or clusters. At about 50 million LY, one finds a very large cluster containing thousands of galaxies – called the Virgo cluster. Some of the observed clusters appear to form super clusters. Our local group and the Virgo cluster are part of one such supercluster which stretches over a diameter of 60 million LY. Local group of galaxies

27. January 10, 2006Astronomy 201027 Farthest galaxy (red object) about 1.3 x 10 10 LY Galaxies are collections of about 10 11 stars  Andromeda galaxy distance 2 x 10 6 LY  nearest star 4.3 LY = 9.6 x 10 12 km = 64,000 AU  Sun 1 AU = 1.5 x 10 8 km

28. January 10, 2006Astronomy 201028 We’ll cover other topics as background: History of astronomy Newton’s laws of motion and gravity Orbits and motion of objects Geology of the Earth Comparative geology of other planets Atoms and light Spectra measured by telescopes Nuclear fusion The Sun and stars Special and general relativity Fusion, black holes, and cosmology

29. January 10, 2006Astronomy 201029 What is Science? A science is a methodological study following the scientific method. The scientific method has 5 steps: Observation Observe some phenomenon to be studied Hypothesis Develop a hypothesis of the phenomenon Prediction Derive a testable prediction from the hypothesis Measurement Make a measurement that tests the prediction Conclusion Verify or refute the prediction, adjust the hypothesis as necessary

30. January 10, 2006Astronomy 201030 Laws of Nature Some scientific hypotheses are so well verified in a wide variety of situations that they become elevated to the status of “laws of nature”. Newton’s laws of motion and gravitation Conservation of momentum and energy Ideal gas law Conservation of mass/atoms Cell theory DNA Evolution

31. January 10, 2006Astronomy 201031 Numbers WordNumberSci. Not.Prefix trillion1,000,000,000,00010 12 Tera (T) billion1,000,000,00010 9 Giga (G) million1,000,00010 6 Mega (M) thousand1,00010 3 kilo (k) 110 0 thousandth0.00110 -3 milli (m) millionth0.00000110 -6 micro (µ) billionth0.00000000110 -9 nano (n) trillionth0.00000000000110 -12 pico (p)

32. January 10, 2006Astronomy 201032 Speed of Light How fast does light travel? About 300,000 km/s = 11,000,000 km/hr The distance that light travels in one year is called a light-year, abbreviated ly = 9.5  10 12 km/year. While this is a large distance, it is useful for quoting distances to other stars. Can be generalized to include light-second, light-day, etc. The Moon is about 1.3 light-seconds from Earth. The Earth is about 8 light-minutes from the Sun.

33. January 10, 2006Astronomy 201033 Astronomy is a Time Machine When we observe a star that is 100 light-years distant, then the light took 100 years to reach us. We are seeing it as it was 100 years ago. The nearest galaxy is about a million light-years from Earth. We see it as it was 1 million years ago. The most distant objects observed are about 10 billion ly from Earth. The light we see left the object 10 billion years ago!

34. January 10, 2006Astronomy 201034 Discussion Question What are some of the things you wish to learn about in this course?