EGS Astronomy Unit Stars constellations and the galaxies

EGS Astronomy Unit

Stars, constellations, and the galaxies Big Bang Theory

Stars and Galaxies • Constellation – A pattern of stars that resemble real or imaginary things • Animals, heroes, gods, etc… – 88 named constellations, each with its own story

Stars and Galaxies • Constellations were used to help create the earliest calendars and for entertainment • Constellations are also used to divide the night sky into sectors to make it easier to find particular stars or planets

Stars and Galaxies • Galaxy- A large-scale group of stars bound together by gravity. – 100 billion stars – 100, 000 light-years in diameter • Speed of light – 300, 000 km/s or 9. 5 trillion km/year – 186, 000 miles/s or 5. 89 trillion miles/year

Stars and Galaxies • Types of Galaxies – Spiral- A bright central region surrounded by spiral arms made of younger stars that circle the center region – Elliptical- Spherical with no spiral arms; no young stars. – Irregular- No particular shape; may be formed as two galaxies collide

Stars and Galaxies • Milky Way Galaxy – Spiral galaxy – 100, 000 light-years in diameter – 2, 000 light-years thick near the center – Our sun is about 30, 000 light-years from the center in one of the spiral arms

Stars • A body of gases that give large amounts of energy in the form of light and heat. • Vary in chemical composition, color, temperature, size, mass, motion, distance from earth, and brightness.

Stars • Chemical Composition – Mostly Hydrogen and Helium with small amounts of carbon, nitrogen, and oxygen – Determined by using spectrum analysis • Every element has a specific spectrum that can be seen using a spectrometer which is capable of taking a source of light and breaking it down to individual wavelengths.

Stars

What is a wave? • A wave is a transfer of energy from one point to another via a traveling disturbance • A wave is characterized by its wavelength, frequency, and amplitude

Wave Properties • Mechanical waves must pass through a medium such as air, water, or solids • Electromagnetic waves do not require a medium and can move through a vacuum

Wavelength (λ) • Distance from successive crest to crest or trough to trough • Measured in meters

Frequency • Number of crests passing by per second • Measured in Hertz (Hz) defined to be one cycle per sec • Equal to the inverse of the amount of time it takes one wavelength to pass by

Amplitude • Maximum displacement of the wave • The amplitude will have different units depending on the type of wave • In a sketch of the wave, it is the distance from the middle of the wave to the peak

Wave Speed Traveling Waves move through space at a certain speed Where, v is the speed of the wave (m/s) λ is the wavelength in meters (m) f is the frequency in Hertz (cycle/s)

Wave Speed • Wave speed is constant for a given medium • The speed of a wave changes only when the wave moves from one medium to another or when certain properties of the medium are varied

Stars

Stars • Color and Temperature – The surface temperature of a star is indicated by its color • • • Blue-white Yellow Orange Red >30, 000 ˚C 7, 500 - 30, 000 ˚C 6, 000 - 7, 500 ˚C 5, 000 - 6, 000 ˚C 3, 500 - 5, 000 ˚C Less than 3, 500 ˚C

Stars • Size – Vary in size from 20 km in diameter to 1000 x larger than our sun – Our sun is 1, 392, 000 km in diameter • Mass – The sun is 330, 000 x more massive than earth – Stars can be 50 x greater or 1/50 smaller than our sun

Stars • Motion of Stars – Apparent motion • Motion of the star as seen by the human eye from earth • Appear to move westward in the sky around Polaris (the North Star) • Due to the rotation of the earth on its axis and its orbit around the sun

Stars • Motion of Stars – Actual motion • Rotate on its axis • Many revolve another star (binary stars) • Move away or toward the earth – Doppler Effect • Blue shift= moving toward earth • Red shift= moving away from earth

Stars • Distance from earth – Light-year: the distance light travels in one year – Speed of light = 300, 000 km/s SO a light-year = 9. 5 trillion km • The sun is 8 light-minutes away from earth • Next nearest star is Proxima Centauri which is 4. 2 light-years away

Stars • Distance from earth – Parallax • A change in position in relation to other stars over a six month period of time • The greater the change, the closer the star – How can we demonstrate Parallax?

Stars • Magnitude – A measure of the brightness of a star – Apparent Magnitude- the brightness as it appears from earth • Affected by distance from earth, size, and temperature – Absolute Magnitude- the true brightness if all stars were the same distance from earth

Evolution of a Star • A star’s life lasts billions of years!!! • Nebula- massive cloud of gas and dust – Increased pressure forms a protostar – Temps get hot enough that nuclear fusion begins • 2 H → 1 He – A star is born

Evolution of a Star • Main-sequence Star – Longest stage • Our sun is about 4. 5 billion years old, with that much life left to go • Third Stage – Hydrogen gone; Explosion; Helium fusion • Giant: 10 x greater in size than the sun • Supergiant: 100 x bigger than the sun

Evolution of a Star • Final Star Stage – Helium fusion ends – Gravity again causes remaining matter to collapse inward – Carbon from helium fusion burns forming a White Dwarf – If the white dwarf stops burning it dies and becomes a Dead Star or Black Dwarf

Evolution of a Star • Sometimes instead of fading away, a white dwarf explodes releasing matter and energy into space forming a Nova • In a supergiant star, after helium fusion is complete, the carbon can fuse into heavier elements which in turn fuse into iron forming a Supernova

Evolution of a Star • Neutron Star- After a supernova, the core may contract into a very small, dense ball of neutrons • Black Holes- matter is compacted so tightly that the gravitational force is greater than the speed of light. May be found at the center of many galaxies.

Evolution of a Star • Formation of Neutron Stars and Black Holes • How do we demonstrate a black hole?