2 “In the beginning…” How did this all start? When did it start? Has it always been this way?How is it changing?What does it all mean?
3 A Quest for Answers Observations of planets, stars, galaxies Analysis of light from stars and galaxiesThinking about these observationsPosing an hypothesisTesting the hypothesisEvidence/tests either support or refute hypothesisLet’s start with the observational evidence
4 The Electromagnetic Spectrum Visible Light Range
14 Doppler EffectWaves emitted from a moving source are shifted depending on direction of motion.Sources moving toward observer show shift toward shorter wavelengths (i.e., toward blue end of spectrum)Wavelength is compressed by motion of source.Referred to as “BLUE SHIFT”
15 Doppler EffectWaves emitted from a moving source are shifted depending on direction of motion.Sources moving AWAY from observer show shift toward longer wavelengths (i.e., toward red end of spectrum)Wavelength is stretched by motion of source.Referred to as “RED SHIFT”
16 Hubble’s Law Nearly all galaxies in the Universe display RED SHIFT The amount of RED SHIFT is related to the relative distance to the galaxy.FARTHER galaxies show GREATER RED SHIFT
17 Normal Spectrum Shifted Spectrum Example of Red ShiftNormal SpectrumShifted Spectrum
18 Hubble’s Law – What does it mean? Is the Earth the center of the Universe after all and everything is moving away from us?Does it depend on frame of reference?Would Hubble’s Law apply if we looked at the Universe from another location?Why is everything moving away?
19 Hubble’s Observation/ Hubble’s Insight All galaxies appear to be moving away from the center of the Universe because the Universe is expanding.The existence of RED SHIFT and the pattern that it shows (greater shift for farther galaxies) is consistent with a pattern produced by an explosion –THE BIG BANG!!
20 The Big BangCurrently the best theory to explain the origin of the UniverseSupported by multiple lines of evidence
21 What was the Big Bang? Prior to the Big Bang – there was no Universe A single super-massive object explodedExplosion creates UniverseMatter, space and time are createdExplosion was approximately 15 billion years ago
22 The Big Bang secondsgenerates space & time, as well as all the matter & energy universe will ever holdFor small fraction of a sec., the universe is an infinitely dense, hot fireball
23 The Universe Takes Shape -- 10-6 sec. universe continues to expand → less dense & cooler.now basic forces in nature become distinct:Gravity & “strong force” (holds nuclei of atoms together), followed by the weak & electromagnetic forces.By end of 1st second, universe consists of particles & energy -- smash together → form protons & neutrons.
24 Formation of Basic Elements -- 3 sec. nuclei of simple elements hydrogen, helium and lithium form(will be another 300,000 yrs before electrons are captured into orbits around these nuclei to form stable atoms).
25 The Radiation Era -- 10,000 years most of the energy left from the “fireball” is in the form of radiation --different wavelengths of light, X rays, radio waves & ultraviolet rays
26 Birth of Stars & Galaxies -- 300 my after BB (still ~ 12 to 15 by before the present).pockets of gas become more and more dense as a result of gravitational attraction.Stars ignite within these pocketsgroups of stars become the earliest galaxies.
27 Birth of the Sun -- 5 Billion Years Before Present (BP) Sun forms w/in cloud of gas in spiral arm of Milky Way Galaxy.vast disk of gas & debris swirls around new star → gives birth to planets, moons, & asteroids .
34 Stars and Planets Each galaxy has about 100 billion stars There are billions of galaxies!Even if only 1% of stars had planets,And even if only 1% of those planets were like Earth,There would still be hundreds of millions of planets that could have life on them!
35 How far are the stars? How big is the Universe? We can measure distances to stars by two methodsOne method – parallax is only good for the very nearest starsThe other method – comparison of magnitudes is more complex, but it can be used for even the farthest stars and galaxies.
36 Parallax Classroom demonstration of parallax Knowing one distance and one angle, we can calculate distance to star using trigonometry
37 Apparent vs. Actual Stellar Magnitude (brightness) Compare how bright the star looks to how bright it would look at a known distanceYou must first know actual magnitude (brightness)
38 How do we know actual magnitude? Cepheid variable stars – absolute magnitude is directly related to period of pulsationSupernova – fixed magnitudeSpectral analysis gives composition, which is related to size, which is related to brightness
39 How close is our nearest neighbor? Proxima centauri is 4.27 light years from Earth
40 What is a light year? The distance that light will travel in one year. Since light travels at 186,000 miles per second,A light year is approximately 6 trillion miles
41 Implications? Distances are enormous!! For some stars, it has taken the light billions of years to reach EarthIn some cases, this means that the star isn’t even there anymore!We see the light that left long ago, therefore…
42 Looking at the night sky is literally looking into the past!!