Astronomy (7.16-7.19)

• Starts as nebula → cloud of dust and gases (mainly hydrogen) which can be pulled together by its own gravity. As the cloud contracts , it bcomes denser and hotter and starts to glow. More mass attaches as the gravitational pull gets stronger and heats the material. This is prostar.
• Temperature and pressure is high enough for nuclear fusion to occur→ forces hydrogen nuclei to fuse together and form helium → star is now in main sequence stage , this is  the stage our sun is currently in.
• Red giant star→ when most the hydrogen has fused into helium , the core is not strong enough to withstand the gravity and collapses and outer layers expand to form red giant( much larger than original star)
• White dwarf star → star throws of a shell of gas and the rest of the star is pulled together by gravity and collapses to form white dwarf
• Black dwarf → fusion reactions no longer occur and it gradually cools over a billion years to become a black dwarf

• Inside a star → gravitaional attraction pulls mass inwards 

                          → radiation pressure from nuclar fusion expands star outwards

• A star like our sun is in equillibrium; the gravitaional force is balanced by thermal expansion
• When all the hydrogen has been fused into helium; the helium nuclei fuses to form a larger nuclei and the star will expand. Thermal expansion is now greater than grvitational attraction.
• When nuclear reactions are finished the star will contract and the gravitational attraction is now greater than thermal expansion causing the star to become a red giant.

• Stars with more mass than the sun are hotter and brighter and fuse hydrogen into helium faster → they become red supergiant stars at the end of main sequence stage.
• that the end of the red supergant stge they rapidly collapse and explode to form a supernova. The outer layers of the red super giant is cast off.
• I f what remains is massive enough, gravity pulls it together to create a balck hole.
• If what remains isn't big enough, gravity pulls it together to form a very small dense star called a neutron star.

• telescope invention at the end of 16th century allowed astronomers to see objects in greater detail.ie the rings of saturn and moons of jupiter
• orbit of jupiters moons backed up heliocentric model
• as telescopes improved more discoveries were made .ie dwarf planet asteroids and comets

ASTONOMY TODAY

• photography allows more detailed analysis and measurments and computer increased speed and detail
• telescopes in orbit allow unobstructed veiw of galaxies, without pollution dust and clouds.
• space probes also allow further investigation into space
• some telescopes are designed to pick up electromagnetic wave emitted of objects in space; sme are also placed in orbit to reduce obstruction.