Astronomy (cont.)Astronomy (cont.)Cosmic MeasurementsCosmic Measurements

Astronomical Unit (AU) Astronomical Unit (AU) - distance from earth to the sun - distance from earth to the sun ~150 million kilometers (93 million miles)~150 million kilometers (93 million miles)- used to express distances to other planets- used to express distances to other planetsLight year – Light year – distancedistance light travels in one year at light travels in one year at

300,000 km/sec (186,000 miles/sec)300,000 km/sec (186,000 miles/sec)- which equals 9.46 x 10- which equals 9.46 x 101212 km km (If 1 ft. equals 1AU, then 120 miles equals 1 light year)

LightyearLightyear Therefore, a light second is 186,000 miles

(300,000 kilometers). A light year is the distance that light can travel in a year, or:

186,000 miles/second * 60 seconds/minute * 60 minutes/hour * 24 hours/day * 365 days/year = 5,865,696,000,000 miles/year

A light year is 5,865,696,000,000 miles (9,460,800,000,000 kilometers).

That's a long way!

Properties of StarsProperties of StarsMass & Size Mass & Size →→ Density Density

- smallest are smaller than Earth- smallest are smaller than Earth- largest are 2000 times bigger than our sun- largest are 2000 times bigger than our sun

Temperature (color)Temperature (color)red red → cooler→ cooler 5,0005,00000 F (3,000 K) F (3,000 K)blue → hottest 40,000blue → hottest 40,00000 F (30,000 K) F (30,000 K)

Properties of StarsProperties of Stars

Composition – done by light spectrum Composition – done by light spectrum analysis, most stars are made of analysis, most stars are made of hydrogen & helium (determined by hydrogen & helium (determined by temperature & compositiontemperature & composition

no two are alike) no two are alike)

Properties of StarsProperties of StarsStar BrightnessStar Brightness

luminosityluminosity – depends on size & – depends on size & temperaturetemperatureapparent magnitudeapparent magnitude – as seen from Earth: – as seen from Earth:brightest are brightest are ≤ 1≤ 1 faintest are ≥ 6faintest are ≥ 6absolute magnitudeabsolute magnitude – expresses luminosity – expresses luminosity of of stars as if they were all seen 32.6 light-stars as if they were all seen 32.6 light-years from Earth (our sun = 4.8)years from Earth (our sun = 4.8)

Life of the Stars: OriginLife of the Stars: Origin

NebulaNebula – huge cloud of – huge cloud of gas and dustgas and dust in in space space

Gravity causes the gas in the nebula to Gravity causes the gas in the nebula to contractcontract to form a to form a ProtostarProtostar (– very (– very young star that is not hot enough to young star that is not hot enough to shine by nuclear fusion shine by nuclear fusion HH22 + H + H22 → → 2He2He2 2 )) this is this is electromagnetic radiant electromagnetic radiant energyenergy

As gravity packs As gravity packs matter more tightlymatter more tightly – the – the protostar’s temperature rises until it reaches protostar’s temperature rises until it reaches a temperature high enough for a temperature high enough for nuclear fusionnuclear fusion to begin to begin

Nuclear fusion is Hydrogen fusing to form Nuclear fusion is Hydrogen fusing to form Helium….Helium….

HH22 + H + H22 = 2He + electromagnetic radiant = 2He + electromagnetic radiant energyenergy

(The minimum temperature required for the (The minimum temperature required for the fusion of hydrogen is 5 million degrees)fusion of hydrogen is 5 million degrees)

When the release of When the release of electromagnetic radiant energyelectromagnetic radiant energy (pushing out) reaches a (pushing out) reaches a balancebalance with the gravity (pushing in) the with the gravity (pushing in) the star stops star stops contractingcontracting and and reaches the stable state. reaches the stable state.

H-R Main H-R Main SequenceSequence

The original mass of the star determines its The original mass of the star determines its temperature and the colortemperature and the color. (Big – glows blue, . (Big – glows blue, medium – glows yellow-orange, small – glows medium – glows yellow-orange, small – glows red)red)

Red Giants / Red Super-giants form as HRed Giants / Red Super-giants form as H22 fuel is used up and gravity overpowers fuel is used up and gravity overpowers released energy, center core contracts released energy, center core contracts while outer layer expands while outer layer expands (He(He22 + He + He22 → C → C fusion starts in the core)fusion starts in the core)

-- outer layers expand and cool (hence it is RED)-- outer layers expand and cool (hence it is RED)

Hertzsprung-Russell diagramHertzsprung-Russell diagramEach star is represented by a dot. One Each star is represented by a dot. One

uses data from lots of stars, so there are uses data from lots of stars, so there are lots of dots. The position of each dot on lots of dots. The position of each dot on the diagram corresponds to the star's the diagram corresponds to the star's luminosity and its temperature luminosity and its temperature

The vertical position represents the star's The vertical position represents the star's luminosity (absolute magnitude). luminosity (absolute magnitude).

The horizontal position represents the The horizontal position represents the star's surface temperature (color). star's surface temperature (color).

http://zebu.uoregon.edu/~soper/Stars/hrdiagram.htmlhttp://zebu.uoregon.edu/~soper/Stars/hrdiagram.html

Life Cycle of StarsLife Cycle of StarsAverage to small stars collapse again after C fuel isAverage to small stars collapse again after C fuel is

used up used up → white dwarf (Earth size)→ white dwarf (Earth size)Large stars (at least 7 times our sun) when fusion (of Large stars (at least 7 times our sun) when fusion (of

carbon) stops, a central iron core is left, intense carbon) stops, a central iron core is left, intense gravitational energy causes further collapse, creates gravitational energy causes further collapse, creates heavier elementsheavier elements→ → explosion causes loss of ½ the stars elements, a explosion causes loss of ½ the stars elements, a supernova is bornsupernova is born

Supernova fades – neutron star is left (core of pureSupernova fades – neutron star is left (core of pureneutrons), eventually gravity overpowersneutrons), eventually gravity overpowers→ black hole is created→ black hole is created

circumpolar circumpolar constellationsconstellations – – constellations constellations that appear to that appear to never set never set below the below the horizon:horizon:

Ursa Major, Ursa Ursa Major, Ursa Minor, Cephius, Minor, Cephius, Cassiopeia, Cassiopeia, and Dracoand Draco

Constellations – a group of stars that Constellations – a group of stars that appears to form a pattern in the skyappears to form a pattern in the sky

Zodiac ConstellationsZodiac Constellations

Constella-Constella-tions tions that that appear appear along along the the eclipticecliptic

Check this out…Check this out…Go and take this quiz:Go and take this quiz:http://aspire.cosmic-ray.org/labs/star_life/starlife_equilibrium.htmlhttp://aspire.cosmic-ray.org/labs/star_life/starlife_equilibrium.html

Good sitesGood siteshttp://aspire.cosmic-ray.org/labs/star_life/http://aspire.cosmic-ray.org/labs/star_life/

starlife_main.htmlstarlife_main.htmlhttp://www.astrophysicsspectator.com/http://www.astrophysicsspectator.com/

topics/stars/FusionHydrogen.htmltopics/stars/FusionHydrogen.html