The Universe. Chapter 14. The night sky . Sky observations date to ancient civilizations Stonehenge was built in England for observing the sky. The differences between stars and planets. Stars Appear as point sources that produce their own light.
Sky observations date to ancient civilizations
Stonehenge was built in England for observing the sky.
Appear as point sources that produce their own light.
They appear to move counter-clock relative to Polaris our north star
Twinkle from atmospheric turbulence
Distance measured in light years (ly): 9.5x1012 km/yr or 6x1012mi/yr.
Visible by reflected light
Celestial objects are projected onto imaginary sphere around the Earth
Celestial equator, is the Earth’s equator projected into the sky.
Altitude angle and azimuth angle determine location on this celestial sphere. They act like latitude and longitude lines in space.
Objects appear to rotate about north/south poles
Gravitational collapse of a gigantic cloud of mainly hydrogen gas and dust produces a Protostar .
When density, temperature and pressure increases until conditions are right for nuclear fusion a star is born.
Temperatures of 10 million K must be reached for hydrogen atoms to be fused to other hydrogen atoms thus causing nuclear fusion.
Diffuses outward over millions of years
Material rising from the interior, cooling, and sinking
Visible “surface” of star
Sun surface temp. ~5,800 K
Plots absolute magnitude and temperature
Each dot = star
Main sequence stars
Converts 1.4x1017 kg of matter to energy each year
About two thousand seven hundred 6000 lb SUVs!
Born 5 billion years ago, should last another 5 billion years.
Lifetime depends on mass
Our sun’s fate could be a white dwarf because of its size.
Less massive stars have longer lifetimes
More massive stars have shorter lifetimes
Differences in stellar brightness is caused by-
The amount of light produced by star
The size of star
The distance to the star
Example- Our Sun
Absolute magnitude = +4.8
Determined by a standard distance
Apparent magnitude = -26.7
How objects looks compared to other objects around it. The more negative the number the brighter the object.
Colors appear as: red, yellow, bluish white
Color related to surface temperature:
Red: cooler stars
Blue: hotter stars
Yellow: in between (Sun)
Based on temperature: hottest to coolest
O, B, A, F, G, K, M
Elements beyond iron created in explosion and distributed throughout Universe
More mass: more gravitational contraction and heat
Critical temperature: 600 million K for supernova
Remaining core between 1.4 and 3.0 solar masses
Gravitational pressure fuses protons and electrons into neutrons
Pulsar: rotating, magnetized neutron star
Remaining core greater than 3 solar masses
Gravitational collapse overwhelms all known forces
Even light cannot escape the dense, compact object
Two gravity bound stars
Most stars are in binary pairs, not ours
Tens to hundreds of thousands or more gravity bound stars
Often share a common origin
Basic unit of the Universe
Billions and billions of gravitationally bound stars
Larger scale still
Clusters of galaxies
Super clusters of galaxies
Billions and billions of galaxies!
Visible as a band in night sky.
Billions of stars
Our nearest neighbors - the Local Group
~1,000 light years across
Nearest dwarf is disrupted gravitationally by the Milky Way
2 million light years away
Very similar to Milky Way
Classification scheme (Hubble)
Elliptical, spiral, barred and irregular
God created the Universe is
the Big Bang Theory
Big Bang Theory
Universe evolved from an explosive beginning about 13.7 billion years ago.
Raisin bread theory
Microwave background radiation
Large scale expansion
Abundances of elements
Diffuse cosmic background radiation
Expansion forever or the big crunch?