1. Introduction to the Universe

2. Topics in this presentation Astronomical numbers Light travel time Composition of universe Why the composition changes –What causes the change? Sizes, distances, and ages Motions Expanding universe, how we measure age

3. Astronomical numbers 1 million = 1,000,000 = 10 6. 1 million sec = 11.6 days 1 billion = 1,000,000,000 = 10 9 (aka. Giga or G). 1 giga-sec = –31.8 years. 1 light sec = distance light travels in … = 300,000 km = 186,000 miles. Almost to the Moon. 1 light year = distance light travels in one year TRIVIA: 1 light year = 6 trillion miles. Nearest star to Sun = 4.3 light-years away. The Sun, all 8 planets are about 4.6 Gyr old. –How many years is that? Universe & everything in it is 13.7 Gyr old (some things weren’t born at the beginning, so are younger)

4. Astronomers can detect a galaxy that is 10 billion light-years away. 1.True 2.False 1234567891011121314151617181920 2122232425262728293031323334353637383940 4142434445464748495051525354555657585960 6162636465666768697071727374757677787980

5. Finding baby & senior citizen galaxies Talk to your neighbor for 1 minute and answer these: Where would astronomers need to look to find galaxies in their earliest stages of life (babies)? –Hint given after 30 seconds. DV: the hint is Unogen. Where would we find galaxies in their later stages (senior citizens)?

6. Light years and observations FOR MORE HELP: See figure 1.5 on p. 9 Lecture Tutorial workbook page 131.

7. Composition of the Universe Stuff in universe (“matter”) Regular matter –Hydrogen (often gas) ~73% –Helium (often inert gas) ~25% –Everything else ~2% Oxygen, Carbon, Iron, Sulfur, Neon, Potassium, etc. Gold, silver, platinum are VERY rare. Dark matter –Matter we can’t see. Infer its existence many ways. Not elements. (“regular”) Dark Energy –Energy we can’t see. Infer its existence by studying accelerating expansion of universe. Book OMITS this from chap 1. Overall 28% 4.6% 23% 72% (half is invisible or hiding)

8. Another visual of universe’s composition

9. Normal matter Everything you know about is made of a few elements –Hydrogen, Helium, Carbon, Nitrogen, Oxygen, Gold Most things are molecules: 2+ atoms –Water (H 2 O), Carbon dioxide (CO 2 ) Science tells us right after the Big Bang, the universe only had 2 elements: –Hydrogen (75%), Helium (25%) –TINY bit of 1-2 more. Where did everything else come from? Book calls it “recycling”. See pages 6-7. Only makes up 2% of matter today. But that’s enough to form planets like Earth, luckily.

10. Ages of a few things When things formed: –The Big Bang = 13.7 billion years ago –The Sun & Earth = 4.6 billion years ago –The Milky Way galaxy = 12-13 billion years ago See the calendar & discussion on page 14.

11. Sizes & Distances Planet order & sizes with hands… In the “Voyage” scale model, 10 billion:1 –Sun is the size of a large grapefruit –Earth is the size of 1mm, located 50 ft from Sun –Moon is ¼ Earth’s size, located 1.5 inches from Earth –Jupiter is … –Pluto is … –Nearest star is named …, size & dist … –Size of Milky Way is … Light travel times to these objects…

12. Are you moving right now? 1.Yes 2.No 1234567891011121314151617181920 2122232425262728293031323334353637383940 4142434445464748495051525354555657585960 6162636465666768697071727374757677787980

13. Motions Daily motion – Earth’s rotation once per __ –Speed varies: ___ for Santa, 1000 mph for Ecuador Yearly motion – Earth’s revolution once per __ –Distance: 1AU = ____ –Speed: average ~66,000 mph –Direction “tilted” 23.5˚ relative to rotation. Sun orbits Milky Way center once per 230 Myr –28,000 ly radius, speed ~500,000 mph –Studying this motion  dark matter discovered Galaxies moving relative to each other. –Nearest galaxies get closer to us. Most move away.

14. Does everyplace on Earth take 24 hours to make one circle around the Earth? 1.Yes 2.No 1234567891011121314151617181920 2122232425262728293031323334353637383940 4142434445464748495051525354555657585960 6162636465666768697071727374757677787980

15. Galaxies outside the Local Group are moving: 1.Towards us 2.Away from us 3.Randomly towards & away 1234567891011121314151617181920 2122232425262728293031323334353637383940 4142434445464748495051525354555657585960 6162636465666768697071727374757677787980

16. Expanding universe means “objects are getting _________”? 1.Further apart 2.Bigger 3.Both further apart and bigger 1234567891011121314151617181920 2122232425262728293031323334353637383940 4142434445464748495051525354555657585960 6162636465666768697071727374757677787980

17. Expanding universe Expansion refers to space between galaxies –Objects don’t grow because … Gravity and other forces hold THINGS together. –Examples: Stars, galaxies, planets, people. We see things moving away Speed away from us depends on distance –Objects twice as far are moving twice as fast –Objects 100x further are moving 100x faster This rule is now called “Hubble’s Law” Let’s see how Hubble’s law works with cars

18. Car “expanding universe” Make a chart like the one I put on the board Car 1 is 60 miles away and travels 30 mph Car 2 is 120 miles away. How fast is it moving if it follows Hubble’s Law? Car 3 is 240 miles away. How fast? How long since Car 1 left you? Car 2? Car 3? How old is the “car universe?” This is exactly what we see with galaxies, except the time is _________ years.

19. Is the composition of the universe changing? 1.Yes 2.No 1234567891011121314151617181920 2122232425262728293031323334353637383940 4142434445464748495051525354555657585960 6162636465666768697071727374757677787980

20. Summary – chapter 1 Astronomical numbers Light travel time Composition of universe Why the composition changes –What causes the change? Sizes, distances, and ages Motions Expanding universe, how we measure age