Chapter 27 Stars and Galaxies Section 1 Characteristics of Stars Notes 27-2.
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Transcript of Chapter 27 Stars and Galaxies Section 1 Characteristics of Stars Notes 27-2.
Chapter 27Chapter 27Stars and GalaxiesStars and Galaxies
Section 1Section 1
Characteristics of StarsCharacteristics of Stars
Notes 27-2Notes 27-2
Distance to StarsDistance to Stars
Light years: used to measure distance to Light years: used to measure distance to stars and galaxiesstars and galaxies– Distance that light travels in one yearDistance that light travels in one year– 300,000 km/s = speed of light300,000 km/s = speed of light– 9.5 trillion km in one year9.5 trillion km in one year– Sun in 8 light minutes from Earth Sun in 8 light minutes from Earth – Proxima Centauri: closest star to Earth (other Proxima Centauri: closest star to Earth (other
than the sun) is 4.2 light years awaythan the sun) is 4.2 light years awaySirius (brightest star): 9 lySirius (brightest star): 9 ly
Polaris: 700 lyPolaris: 700 ly
Distance to StarsDistance to Stars
Parallax: method used to determine the Parallax: method used to determine the distance to starsdistance to stars– Because the earth is moving the star appears Because the earth is moving the star appears
to shift in the sky depending on the time of to shift in the sky depending on the time of yearyear
– The closer the star is to the earth the greater The closer the star is to the earth the greater the shiftthe shift
– Astronomers use a photo to determine the Astronomers use a photo to determine the shift (photographed twice in a 6 month time)shift (photographed twice in a 6 month time)
Then calculate the distance to within 1000 lyThen calculate the distance to within 1000 ly
ParallaxParallax
Distance to StarsDistance to Stars
Astronomers compare the actual Astronomers compare the actual brightness and apparent brightnessbrightness and apparent brightness– Determines the distance from the earthDetermines the distance from the earth
Cepheid (Sef-EE-id) variable starCepheid (Sef-EE-id) variable star– Star’s brightness varies at a constant patternStar’s brightness varies at a constant pattern
Brightens and fades in a cycle that can be used to Brightens and fades in a cycle that can be used to determine how far away it isdetermine how far away it is
– Astronomers can then determine the distance Astronomers can then determine the distance to the galaxy it is in to the galaxy it is in
Stellar MagnitudesStellar Magnitudes
3 billion stars can be seen through 3 billion stars can be seen through telescopes on the surface telescopes on the surface – 6000 can be seen with the unaided eye6000 can be seen with the unaided eye
Over a trillion stars can be seen with the Over a trillion stars can be seen with the Hubble Space TelescopeHubble Space Telescope
Apparent Magnitude: brightness as it Apparent Magnitude: brightness as it appears from Earthappears from Earth
Absolute Magnitude: brightness as it Absolute Magnitude: brightness as it appears 32.6 ly awayappears 32.6 ly away
Apparent MagnitudeApparent Magnitude
The measurement of brightness is The measurement of brightness is assigned a number on a scaleassigned a number on a scale– Brightest stars have lowest numbersBrightest stars have lowest numbers– Dimmest stars have highest numbersDimmest stars have highest numbers
Most powerful telescopes can detect an Most powerful telescopes can detect an apparent magnitude of 29apparent magnitude of 29
Apparent MagnitudeApparent Magnitude
Unaided eye can detect a 6Unaided eye can detect a 6– Called a sixth magnitude starCalled a sixth magnitude star– First magnitude is one of the brightest in the First magnitude is one of the brightest in the
skysky
If the number is negative it is brighter If the number is negative it is brighter than the first magnitude starthan the first magnitude star– Sun (-26.8), Moon (-12.5), Venus (-4.6), Sun (-26.8), Moon (-12.5), Venus (-4.6),
Jupiter (-2.7), Sirius (-1.46)Jupiter (-2.7), Sirius (-1.46)
Absolute MagnitudeAbsolute Magnitude
Brightness from 32.6 lyBrightness from 32.6 ly
Ex: If the sun was 32.6 ly away, it would Ex: If the sun was 32.6 ly away, it would be a fifth magnitude star.be a fifth magnitude star.– Its absolute magnitude = +5Its absolute magnitude = +5
Most stars are between a -5 and +15Most stars are between a -5 and +15
Absolute MagnitudeAbsolute MagnitudeEach star has two magnitudesEach star has two magnitudes– Two depend on the distance the star is from Two depend on the distance the star is from
EarthEarth
Stars with a low apparent mag. and higher Stars with a low apparent mag. and higher absolute mag. appear brighter than if they absolute mag. appear brighter than if they were 32.6 ly awaywere 32.6 ly away– Like the SunLike the Sun
Stars with a high apparent mag. and low Stars with a high apparent mag. and low absolute mag.absolute mag.– Stars are too far away to look brightStars are too far away to look bright
Absolute MagnitudeAbsolute Magnitude
How far away is a star with apparent mag. How far away is a star with apparent mag. of +7 and absolute mag. of +7?of +7 and absolute mag. of +7?
32.6 light years32.6 light years
HR DiagramHR Diagram
Graph plotting the surface temperatures Graph plotting the surface temperatures versus the absolute magnitudes of starsversus the absolute magnitudes of stars
HR diagram (Hertzsprung-Russell)HR diagram (Hertzsprung-Russell)– Ejnar HertzsprungEjnar Hertzsprung– Henry RussellHenry Russell– Both discovered the patternBoth discovered the pattern
Brightness increases as the surface Brightness increases as the surface temperature increasestemperature increases
HR DiagramHR DiagramMain sequence starsMain sequence stars– Found in the band running down through the diagramFound in the band running down through the diagram– SunSun
Giants:Giants:– Large and coolLarge and cool– BetelgeuseBetelgeuse
Supergiants:Supergiants:– Very large and coolVery large and cool– AntaresAntares
White DwarfsWhite Dwarfs– Hot and smallHot and small– About the size of EarthAbout the size of Earth
HomeworkHomework
Sticky NotesSticky NotesKey Terms Ch. 27Key Terms Ch. 27
Due: Wednesday, Dec. 9Due: Wednesday, Dec. 9