Ch. 30 - Stars•The Sun accounts for more than 99% of the mass in the solar system.

–The Sun is 330,000 times as massive as Earth.–It would take 109 Earths end to end to fit across the

Sun.•The Sun’s mass controls the motion of the planets and other objects in the solar system.•The Sun’s density in the center is 150,000 kg/m3.•This is 13 times the density of lead.

–A pair of dice would weigh about 2 lbs.•The temp. is about 10,000,000 K in the center.

–These gases become plasma at this temp.•Video

SUN• Galileo was the first to study the Sun in

detail.• Use solar telescopes to study the Sun

today.• Sun is 110 times larger than the Earth.• How long does it take the radiation to

reach the Earth?–8 minutes 33 sec.

• The Sun’s surface is about 5,500 C.• Video

Regions of the Sun• 1. Photosphere – inner most layer, yellow

surface with granules or blotches. Average temp. = 5,800 K–Fig. 30-1 (pg. 806)

• 2. Chromosphere – the outer atmosphere above the photosphere.–Fig. 30-1

• 3. Corona – above the chromosphere with a vacuum like atmosphere. –Fig. 30-2 (pg. 807) – Temp. range of 1 to 2

million K• Video

• Solar winds come off the corona and fly towards the Earth.–The charged particles from the solar winds

are deflected by Earth’s magnetic field and collide with gases in Earth’s atmosphere producing auroras.

• Auroras are “Northern Lights” produced by solar winds.

• Sunspots are darks spots with a lower temperature than the surface, thus the dark color. They last about 2 months.–Sunspots reach a maximum number every

11.2 years.

• Solar flares are extensions in the corona. They are violent eruptions from the Sun’s surface.

• Prominence is an arc of gas that is ejected from the chromosphere. Like solar flares prominences are associated with sunspots.

• All of this energy comes from the center of the Sun where fusion occurs.

• Video

Spectrum• Visible Light Spectrum. What are the colors?

– ROYGBIV• 3 Types• 1. Continuous spectrum – produced by a flowing solid

or liquid, or by a highly compressed, glowing gas. It can also be produced by a prism (refracting the light).

• 2. Emissions spectrum – comes from a noncompressed gas in which bright lines occur at certain wavelenghts.– The lines are dependent on the element being observed.

• 3. Absorption spectrum – causes a series of dark bands. These bands are produced from different chemical elements that absorb light at specific wavelengths. – They can be used to identify gas in a star’s outer layers.

Constellations• Constellation is a group of stars that forms

a pattern in the sky. 88 total.• Big Dipper Ursa Major or big bear• Little Dipper Ursa Minor or little bear• North Star Polars• Draw all three• Cassiopeia is a lopsided M above the little

dipper.• Video – Looking North• Video – Looking South

• Circumpolar constellations circle around polaris–Ursa Major, Ursa Minor, Cassiopeia

• Winter Constellations–Orion’s Belt & the hunter

•Sirius is the left star on Orion’s belt the brightest star in the sky.

• Summer Constellations–Northern Cross

• Appendix K – pg. 922

Horoscope Constellations• Aries• Taurus• Gemini• Cancer• Leo• Virgo• Libra• Scorpion• Sagittarius• Capricorn• Aquarius• Pisces

• When we look at stars in the sky at night they seem to be close to each other. However, we see them in a 2-dimensional view (we can’t see the depth of the stars = 3-D).

• This means that stars from a constellation may not be close to one another at all.– Illustrate

• Binary star are 2 stars gravitationally bound together and orbit a common center of mass.– More than ½ the stars in the sky are binary or multiple-star

systems.

• 2 units of measurement are used by astronomers.– 1. light years = 9.46 x 1012 km– 2. parsec = 3.26 light years (3.09 x 1013 km).

• Parallax – the apparent shift in position caused by the motion of the observer.– The position of the Earth changes as it orbits the

Sun. This causes a nearby star to appear to change its position as well.

– The closer the star, the larger the shift.– The distance to the star can be estimated by its

parallax shift.• A parsec is defined as the distance at which an

object has a parallax of 1 arcsecond.– Astronomers use this method to record distance up

to 500 pc or 1500 ly.

• A star has the following properties: mass, diameter, brightness, composition, surface temp., and energy output (power).

• Magnitude – how bright it appears.– Used by ancient Greeks – now we use apparent magnitude.

• Apparent Magnitude – how bright an object appears to be.– A +1 star is 100 times brighter than a +6 star.– Negative numbers are assigned to the brightest objects.

• Absolute Magnitude – the brightness of an object is placed at a distance of 10 pc.– This system takes into account distance.– This can only be calculated when actual distance is known

for that object.

• Luminosity – measures the energy output from the surface of a star per second.– Need apparent magnitude & distance.

• A star’s spectra (absorption spectra) is used to determine the type of star and categorize it.– In order of hottest to coldest: O, B, A, F, G, K, M.

• Cooler stars have more absorption bands than hotter stars.– Fig. 30-15 (pg. 818)– Most stars have 73% H & 25% He.

• Activity

• The red end of the spectrum means there are longer wavelengths coming from the star.–This means the distance between the star &

the Earth are increasing–This is the Doppler effect.–This usually means the star is moving away

from the Earth.• The blue end of the spectrum means shorter

wavelengths are coming from the star.–This means the distance between the star

and the Earth is decreasing.–This usually means the star is moving

towards the Earth.

H-R Diagrams• This uses the relationship between a star’s

absolute magnitude, surface temp., and spectral type to distribute stars.

• The main sequence shows that stars follow a pattern in decreasing surface temp.

• The outliers are the Supergiants, Giants, and White dwarfs.

• Video

• What is the next closest star?–Alpha Centauri

• What is the closest star?–Sun–150 million kilometers–93 million miles–40 trillion kilometers –4.3 light years away

• Light-years are used to measure space distance 5.8 trillion miles

• What is the speed of light?–300,000 km/sec. or 186,000 miles/sec–Light travels at 9.5 trillion kilometers per year.

• Star Size–Some stars are smaller than the Earth.–Some are 2,000 times larger than the Sun–Some are very dense, others are not.

• 1 teaspoon of Sirius’ mass would weigh more than a ton on Earth.

–Most stars have similar masses as the Sun.• Star Temperatures

–White & Blue stars are the hottest• 30,000 degrees C

–Red stars are the coldest.• 3,000 degrees C

–The Sun’s temperature is about 5,500 C.

• Sirius is a hot blue-white star.• Aldebaran is a cooler red star.• Supergiants are the largest stars• Giants are next• Dwarf stars are the smallest.

– These are very dense.

Stellar Evolution• Stars are thought to have formed from

hydrogen & a cloud of dust.• A nebulae is a forming star.

– Video• When the forming star becomes dense enough

& hot enough to glow it is called a protostar.–Fusion occurs once it gets hot enough.–Video

• It takes a few thousand years to form a white star.

• It takes about 10 billion years to reach its death.

• A star will then go through the main sequence from: blue, yellow, orange, red.

• Red is towards the end of their lifespan.• Most stars maintain a steady brightness, but

there are a few that blink. Why do you suppose they blink?

• Variable stars are the ones that vary in brightness (blinking).

• Pulsating stars expand & contract as they change in brightness. Very slow change in brightness, sometimes days.

• Pulsars are stars that release light and radio waves as it flickers. These are believe to come from dying stars (supernovas).

• As a star dies out it forms a Red Giant.–Helium builds up in the core from this.

• A White Dwarf is the final stage in a star’s lifespan, in which the energy from fusion reactions are used up.–They then start to pulsate this is called a

Nova.–Finally, the white dwarf explodes with

half of its mass blown away in a huge cloud of dust.•This is called a Supernova• Video

• Neutrons stars are the remaining part of a supernova.–Electrons & protons collapse to form a

extremely dense neutron. The resistance of the dense neutrons cause the collapse of the core to stop.

• Black Hole–If the Neutron star is too dense for the

neutrons to stop the collapse in which the core collapses forever, then a black hole will form. The collapse doesn’t allow light to escape.

–Video