Download Characteristics of Stars

Characteristics of Stars
Characteristics of Stars
Distances and Size
 Magnitude
 Elements
 Mass and Temperature
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Distances and Size
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The Astronomical Unit is used within the solar
system
It is 93 Mmiles or the distance from the Earth to the
sun
Distances
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Kilometers ( or miles) can be used to measure the
sizes of planets
Distances and Size
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The sun is the standard unit for the size of
stars
Distance and Size
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Sirius is 2.5 suns and Pollux is 4 suns
Distances and Size
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Betelgeuse is 1000 suns
Distance and Size
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The distances to stars can be measured by
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Light years
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The distance light travels in 1 year
300,000 km/sec
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This is 9.5 trillion km in 1 year
Proxima Centauri is 4.2 ly away or 39,900,000,000,000 km
or 24.8 trillion miles
 The circumference of the Earth is ~25,000 miles
Parsecs
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3.26 ly
When a star is this far away it starts showing parallax
Distances to stars are also measured in parsecs
Parallax Explained
(Do Not Write This Slide Down… Just Read And Try)
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Parallax measurements take advantage of the fact that, as the
Earth orbits around the Sun, relatively near-by stars appear to
move with respect to the fixed, very distant stars (see the
diagram below). This is the same thing that happens when you
look at a close object with first one eye and then the other.
For example, hold your thumb at the tip of your nose. Look at
your thumb with first your right eye and then your left. Your thumb
appears to move because your eyes are not at exactly the same
place, so each eye views the thumb from a different angle. Now
hold your thumb at arm's length and repeat the experiment. Your
thumb will still appear to shift, but will not appear to move as
much as it did when it was closer.
The same thing happens to stars. The closer stars appear to shift
more than the farther stars. The "fixed" background stars are not
really fixed; they are just so far away that we cannot distinguish
their apparent shift. The apparent shift of the stars is called their
parallax.
Parallax
Parallax Continued (2 Examples)
km, parsec, AU, light year, meter
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Put these distances in order from smallest to
largest
km, parsec, AU, light year, meter
(Smallest) Meter, km, AU, Light Year, Parsec (Largest)
Magnitude (the brightness of a star)
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Apparent Magnitude
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Luminosity
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Absolute Magnitude
Apparent Magnitude
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How bright a star appears to be
Dependent on
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Distance from Earth
Not standardized
Does not reflect a star’s true brightness
Luminosity
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The actual brightness of a star
Depends on
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Size
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Bigger = Brighter
Temperature
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Hotter = Brighter
If 2 stars were the same size but star A was 6000º=C and
star B is 10,000ºC, which one would be brighter?
Absolute Magnitude
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The way astronomers express true
brightness or luminosity
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How bright the stars are if they were lined up 10
parsecs away from Earth
Depends on
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Size and Temperature
The more negative a # the brighter the star
Absolute Magnitude
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Put these stars in order from brightest to
dimmest (1=brightest 4=dimmest)
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Antares: -5.38
Procyon:+2.62
Spica: -3.55
Sirius: +1.42
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1
4
2
3
** Look at the chart on
623. Which star has the
brightest apparent
magnitude?
Elements
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By now you should know how scientists
determine what elements are in stars
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(comparing emission and absorption spectra!)
Hydrogen and Helium are found in the
greatest quantities
All of the other elements are found in various
amounts
No 2 stars have the same exact make-up of
elements
Mass and Temperature
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Mass – Difficult to measure
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Observations such as gravitational influence are
used to determine this
Compared to sun (like size)
Temperature – determines the color
Temperature and Color
HOT
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Blue stars are hotter
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COOL
Blue light has a shorter wavelength, this means it
has more energy
Red stars are cooler
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Red light has a longer wavelength, this means it
has less energy