ASTRONOMY Astronomy is a natural science that studies

ASTRONOMY

• Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry in an effort to explain the origin of those objects and phenomena and their evolution

How did it all begin? ? Big bang 5 min

Forget the big bang, tune in to the big hum THE big bang sounded more like a deep hum than a bang, according to an analysis of the radiation left over from the cataclysm. Physicist John Cramer of the University of Washington in Seattle has created audio files of the event which can be played on a PC. "The sound is rather like a large jet plane flying 100 feet above your house in the middle of the night, " he says. Giant sound waves propagated through the blazing hot matter that filled the universe shortly after the big bang. These squeezed and stretched matter, heating the compressed regions and cooling the rarefied ones. Even though the universe has been expanding and cooling ever since, the sound waves have left their imprint as temperature variations on the afterglow of the big bang fireball, the so-called cosmic microwave background. Cramer was prompted to recreate the din- last heard 13. 7 billion years ago- by an 11 -year-old boy who wanted to know what the big bang sounded like for a school project. To produce the sound, Cramer took data from NASA's Wilkinson Microwave Anisotropy Probe. Launched in 2001, the probe has been measuring tiny differences in the temperature between different parts of the sky. From these variations, he could calculate the frequencies of the sound waves propagating through the universe during its first 760, 000 years, when it was just 18 million light years across. At that time the sound waves were too low in frequency to be audible. To hear them, Cramer had to scale the frequencies 100, 000 billion times. Nevertheless, the loudness and pitch of the sound waves reflect what happened in the early universe. During the 100 -second recording (http: //www. npl. washington. edu/AV/Big. Bang. Sound_2. wav), the frequencies fall because the sound waves get stretched as the universe expands. "It becomes more of a bass instrument, " says Cramer. ###

The universe started as a single point. That point was extremely dense. It became unstable and exploded outward. Today the universe continues to expand.

• Scientists believe the Big Bang occurred between 1215 billion years ago!

Hubble’s Law: Nearby galaxies are moving away slowly while more distant galaxies are moving away more quickly.

What is the Doppler effect? Doppler effect 3 min Shelden episode 2 min

It's the apparent change in the frequency of a wave caused by relative motion between the source of the wave and the observer.

DO NOW: ANSWER THIS At rest Moving Which way is the shift? WHAT DOES IT MEAN?

How BIG is the Universe?

MEASURING DISTANCE • Distances between celestial objects are extremely large. • Rather than miles, astronomers refer to a light-year as a standard unit of distance. • One light-year is the distance light travels in one year.

• The speed of light is 186, 000 mps (300, 000 kps). • Thus, one light-year is about 6 trillion miles. • The nearest star to us (Proxima Centauri) is 4. 2 light-years away.

ASTRONOMICAL UNIT • Another unit of distance is the Astronomical Unit (AU). • One AU is the distance from the Earth to the Sun (93 million miles) • Distances to other objects are given in multiples of AU.

THE DISTANCE FROM THE SUN TO NEPTUNE, THE FARTHEST PLANET FROM THE SUN IS 30 AU. HOW MANY TIMES GREATER, IS THE DISTANCE FROM THE SUN TO NEPTUNE, COMPARED TO THE DISTANCE FROM THE SUN TO EARTH Remember: 1 AU = distance Sun – Earth = 150 million km

GALAXIES Galaxy 2 min

• A galaxy is a collection of millions or billions of stars. • Galaxies can be spiral, elliptical, spherical or irregular in shape.

n. The Sun is part of the Milky Way galaxy, which is a spiral galaxy. n. The Sun is located on one of the spiral arms, far from the galactic center.

Size of our Milky Way galaxy

Put these in order of size: galaxy universe solar system universe galaxy solar system

REGENTS QUESTION Which sequence correctly lists the relative sizes from smallest to largest? (1)our solar system, universe, Milky Way Galaxy (2)our solar system, Milky Way Galaxy, universe (3)Milky Way Galaxy, our solar system, universe (4)Milky Way Galaxy, universe, our solar system

REGENTS ANSWER (2) our solar system, Milky Way Galaxy, universe

e h t d l u o ? c d n w E Ho erse v i Un Death universe

Crash course astro

A STAR IS A BALL OF GAS THAT PRODUCES ITS OWN ENERGY. THEY ARE GROUPED IN LARGE STRUCTURES CALLED GALAXIES. (MILKY WAY). STARS HAVE LIFE-CYCLES LIKE HUMANS.

• Stars vary in their size, mass, density, temperature and composition. Size of stars compared

• Luminosity – the actual brightness of a star • Luminosity depends only a star’s size and temperature

COMPOSITION • Stars are primarily made of Hydrogen and Helium • Many other elements are present in stars in small amounts • A star’s composition can be determined by spectral analysis.

SPECTRAL ANALYSIS • Spectral analysis is the study of the electromagnetic spectrum emitted by a star, using a spectroscope. • Each element emits radiation is a specific set of wavelengths 4: 16

ELECTROMAGNETIC SPECTRUM

COLOR AND TEMPERATURE n. A Star’s color depends upon its surface temperature. •

THE H-R DIAGRAM • The Hertzsprung-Russell (HR) Diagram is a graph of stars, comparing luminosity and temperature.

ESRTs p 15

ESRTs p 15

ESRT p 15 What type of star is our Sun classified as? Circle where it is on the chart

THE H-R DIAGRAM • Main Sequence – band into which most stars • • spend their lives. Red Giants and Supergiants – cooler, very luminous stars that are very large White Dwarfs – hotter, low luminosity stars that are small

THE H-R DIAGRAM

REGENTS QUESTION Which statement describes the general relationship between the temperature and the luminosity of main sequence stars? (1) As temperature decreases, luminosity increases. (2) As temperature decreases, luminosity remains the same. (3) As temperature increases, luminosity increases. (4) As temperature increases, luminosity remains the same.

REGENTS ANSWER (2) As temperature increases, luminosity increases.

REGENTS QUESTION Compared to other groups of stars, the group that has relatively low luminosities and relatively low temperatures is the (1)Red Dwarfs (2)White Dwarfs (3)Red Giants (4)Blue Supergiants

REGENTS ANSWER (1)Red Dwarfs

STAR LIFE CYCLES • Stars are born in a cloud of gas and dust, called a nebula. • The gravity pulls together thegases to form a protostar. • When temp. is hot enough, fusion begins, and a star is born. • Most stars remain as main sequence stars, until their hydrogen fuel is depleted Star birth 2: 25

The star will remain a Main Sequence star, until its fuel, (Sun…hydrogen) runs out

An average star, like the sun, will go then explode, to become a Red Giant, eventually becoming a White Dwarf. Sun explodes…

• A large star would become a Supergiant, then explode as a supernova. The result may be a neutron star, pulsar or black hole. 1 st black hole pic Life cycle of stars