Science 4.2

Stars differ in size, brightness, and temperature
Star’s Brightness : amount of light a star gives off + distance from the Earth
What unit do we use to measure distance between stars?
: light year (distance light travels in one year, approx 9.5 trill km)
How do we measure distance?
by using parallax: the apparent shift in the position of an object when viewed from
different locations

To measure the parallax of a star,
astronomers plot the star’s position in the
sky from opposite sides of Earth’s orbit
around the Sun.

Size
White dwarfs <> differences in color
* Sun = a yellow, G-class star

Stars have Life Cycles
Stars are not permanent -> go through life cycles of birth, maturity, and death

Birth
stars form from a nebula (cloud of gas + dust)
-> gravity pulls gas & dust closer together =contracts
-> forms hot, dense sphere
Maturity
sphere becomes a star if center is hot enough for fusion to occur
Death
its matter does not disappear
i) some of it may form a nebula or.. ii) move into existing nebula -> may become part of new star

Stages in the Life Cycles of Stars difference in mass = difference in life cyclemain sequence: the stage in which stars produce energy through the fusion of
hydrogen into helium

Neutron Star
def: extremely dense core left behind in a supernova
-mass 1~3x’s bigger than the Sun
-some emit beams of radio waves as they spin called pulsars (they seem to
pulse as the beams rotate)

Black Hole
-core more than 3x’s bigger than the Sun
-> core collapses -> form invisible object called a “black hole”
-gravity of a black hole is so strong that no form of radiation can escape

Star Systems
- most stars do not exist alone, held together by gravity
ex) binary star system (2), multiple star system (>2)

important source of info about star masses
-> astronomers cannot measure mass directly
they use the gravity in star systems to calculate star mass