Measuring Distances in the Cosmos

Newton 17 th century calculated that Sirius (one of the brightest stars was 1 million times further away than the sun (1 million AU) –Compared brightness of Sirius to brightness of Saturn Actual distance to Sirius = 550,000 AU

Measuring with Triangulation and Parallax  Triangulation  Method of measuring distance indirectly  Done by creating an imaginary triangle between an observer and an object who’s distance needs to be discovered Copy

Triangulation  A) Create a baseline –In this case line A to C  B) Measure angles from the two points on the baseline –In this case Angle A and Angle C  C) Make a scale drawing of the triangle using a protractor and a ruler Copy

Greeks Used triangulation 2000 years ago to calculate the distance between the Earth and Moon –Baseline was 300 km –Also knew they would have to take into account the curvature of the Earth.

Parallax  Is the apparent shift in position of a nearby object when it is viewed from two different points. –Eg: Point finger close one eye then the other eye. Using Earths orbit –Sightings are taken 6 months apart –If a star is close enough it will appear to move relative to more distant stars Copy

Light Years  Represents the distance light travels in one year (63,240 AU) –Closest star to Earth = Proxima Centauri ( AU) 4.28 light years away Copy

Cepheid Variables  Are stars that change size and brightness (they pulsate) –Cepheids pulsate in predictable fashion –Two Cepheids would pulsate (go bright then dim) at the same time They would have to reach the same brightness If they didn’t the reason was due to distance  By classifying Cepheids according to their maximum brightness  Astronomers have been able to use them as a standard against which to analyze other variable stars Helped measure accurate distance of milky way galaxy Copy

The Milky Way  Appears as a white hazy band extending from south horizon across overhead sky –May look like thin haze of clouds –Actually a vast accumulation of 400 billion stars  Galaxy  Is a collection of stars, gas and dust held together by gravity Copy

Star Clusters Some stars occur in clusters  Open Clusters: are collections of 50 to 1000 stars that appear dispersed along the main band of the Milky Way Eg: Pleiades  Globular Clusters: are collections of to 1 million stars arranged in distinct spherical shapes.  Eg: Hercules Appear not along the band of the milky way but in the southern region of the sky Copy

Mapping the Size and Shape Harlow Shapley (1918) –Mapping galaxy using Cepheid Variables –Resulted in new picture of galaxy  Milky Way Galaxy  Disk shaped  Halo of Globular Clusters surrounding center  Sun was nowhere near the center of the galaxy –75,000 Light-Years in diameter –Sun is 25,000 Light-Years from center of galaxy Copy

Andromeda and Beyond  Most distant object seen by the unaided eye is constellation Andromeda –1925 Edwin Hubble spotted stars in the nebula  Realized it was not a cloud of dust and gas but another Galaxy Scientists have now found hundereds of galaxies (“island universes” – as called by Hubble) Copy

Types of Galaxies Three major types  Elliptical  Most common  Shaped like a football  Made of old stars, and little inter-stellar dust and gas  Spiral  Flat pinwheels with arms spiralling outward from a central region  Composed of dust gas and young blue stars (star formation still occurring)  Irregular  No shape, mixture of young and old stars embedded in dust and gas  Smaller and less common than the other two types Copy

Galaxy Clusters  Galaxies also occur in clusters throughout the universe –Eg: Milky Way and Andromeda Galaxy are two of 30 galaxies that make up a cluster called the “Local Group” Copy

The Cosmic Speedometer  Spectroscopes also allow us to tell how fast an object is moving towards or away from us –Eg: You may have noticed that the siren on an ambulance sounds different as the vehicle approaches, passes then moves away  This is called the Doppler Effect –Same technology used by Police radar guns  When object is not moving the sounds have uniform pitch in all directions because waves are uniform  When the object is moving the distance between sound waves is changed so the pitch changes Higher as it moves toward something, Lower as it moves away. Copy

Cosmic Speedometer Light like sounds moves in waves so the Doppler effect can be used to measure the speed of light emitting objects –If a star is approaching the wavelength becomes compressed and the stars spectrum becomes shifted towards the blue end (blue-shift) –If a star is moving away the wavelengths become red-shifted (more elongated)

Discovery of the Expanding Universe 1929 Edwin Hubble estimated the distance to 46 Galaxies.  Discovered all galaxies were red- shifted  This means they were all moving away from earth  The furthest away were moving the fastest…the closest galaxies were moving slower  This became known as HUBBLES LAW Copy

Determining the Beginning of Time Origin of Matter  Big Bang theory  billion years ago  Universe is expanding therefore it must have started off small and dense –Echos of the Big Bang 1960 microwave antenna kept detecting background noise Picking up radiation given off by original Big Bang event Copy

Quasars  1960 astronomers discovered star-like objects that emit great amounts of radio waves  Result of explosions produced by colliding galaxies Collisions of galaxies forced huge amounts of star material into a central black hole. This was converted into light energy Copy

Gamma Ray Bursts  Powerful burst of energy (more energy in seconds than the sun can emit in it’s entire life)  Predict:  Two stars collide or collapse forming a black hole releasing a large amount of energy Copy

Missing Mass  Galaxies occur in clusters  Astronomers added up the mass of all the matter in the Galaxies (60-70 percent of estimated mass was missing) Suggest there may be burned out stars we can’t see that have mass Empty space contains neutrinos – elementary particles that carry no charge Copy