Download Locating Objects in Space

Locating Objects in
Space
Constellations
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88 constellations in the night sky
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28 northern hemisphere, 12 zodiac, 48 southern hemisphere
Used as navigational guide
Each culture has different names, all recognize the same
star groupings
Greek letters are used for identifying the brightest stars
in constellations
 Alpha
 Beta
γ Gamma
Bright
Dim
Reference Points
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Zenith – point directly above you in the sky
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Celestial Sphere – imaginary sphere surrounding the earth
on which the stars are located (Stars only appear to be on
celestial sphere)
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Celestial Poles – extensions of earth’s geographic poles
(North Pole – Polaris…the pole star)
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Celestial Equator – extension of Earth’s equator
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Ecliptic – apparent path of the sun on the celestial sphere
Celestial Coordinates: “directions”
to help you find objects in the night
sky
•Declination: degrees North &
South of the celestial equator
*like latitude on Earth or
altitude above the horizon
•Right Ascension: hours, minutes, &
seconds east of the vernal equinox
(where the celestial equator and
ecliptic cross one another)
*like longitude on Earth
Zodiac Constellations: 12
constellations through
which the sun passes in a
years time (found along
ecliptic)
Circumpolar Constellations:
constellations that can be
seen throughout the year
at your latitude (“circle
the pole”)
How do we locate the planets?
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All planets orbit within a few degrees of the ecliptic
Superior Planets (Jupiter – Neptune) can generally be
seen any night, except when on the opposite side of the
sun
Generally move eastward in celestial sphere from night
to night
Retrograde Motion – occasional westward motion due
to Earth “overtaking” the planet in its orbit
Planets – December 2008
Planets – April 2009
Visible in the morning sky
Properties of Stars
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Can be measured in terms of diameter, mass,
brightness, energy output (power), surface
temperature, & composition
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Diameters: range from 0.1 times the Sun’s
diameter to 100 times larger
Mass: ranges from 0.01 to 20 or more times the
Sun’s mass…some are 50 – 100 times the Sun’s
mass but are extremely rare
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Apparent Magnitude: how bright a star appears to
be.
Ranges from 1st – 6th magnitude, 1st is 100 times
brighter than 6th
 Difference of 1 magnitude corresponds to a factor of
2.512 in brightness
 Does not take into account the distance of the star
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Absolute Magnitude: the
brightness of an object
if they were all lined up
at the same distance away
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Changes the scale a bit
since distance is taken
into account
Sun is brighter than Sirius
on apparent magnitude
scale, but less bright on
absolute magnitude scale
Determine distance using
parallax – apparent shift in
position of star caused by
motion of observer
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Luminosity: total amount of energy given off by
a star
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Depends on distance and magnitude
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Extremely wide range (millions of times greater than the
sun to thousands of times less than the sun)
Composition:
Hydrogen and Helium make up 98% of all stars
 1 – 2 % Oxygen, Carbon, Nitrogen, Calcium
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Temperature: determined by star’s spectrum (hotter
the star, greater the ultraviolet and less the
infrared rays)
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Spectral classes: O, B, A, F, G, K, M
(Oh Boy An F Grade Kills Me!)
O is the hottest and M is the coolest
 Each class is divided into 10 subdivisions labeled
0 to 9 (a B1 star is hotter than a B8 star)
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H-R Diagrams
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Hertzsprung – Russell Diagrams compare luminosity
and temperature
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Main sequence stars (80-90%) trend from faint, cool stars in
lower right to hot, bright stars in upper left
Giants and Supergiants - located above main sequence
White dwarfs – stars located below the main sequence
Largest stars in the upper right and smallest stars in the
lower left
Five Luminosity Categories: I. supergiants, II. bright
giants, III. giants, IV. subgiants, V. main sequence
Our Sun is a G2V star
Stellar Evolution
Mass: determines type of length of the life of a star
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The more massive a star, the shorter its life will be
Stages of Life:
1.
Nebulas: begin as huge clouds of gas and dust
2.
Protostar: gravity causes nebula to contract or collapse
on itself forming a disk shape
i.
ii.
iii.
During early stages, not yet hot enough for nuclear fusion &
emits no visible light
Core temperatures finally reach 8-10 million Kelvins, high
enough for nuclear fusion & star is “born”
Hydrogen is converting to Helium
A - North American Nebula - emission nebula
B - Jewel Box open cluster
C - Globular Cluster 47 Tucanae
D - Cygnus Loop - supernova remnant
Three main evolutionary paths based
on initial mass of star
1st Path: (0.1 to 8 solar masses)
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Main Sequence – lifetime determined by amt of
fuel available & rate of consumption
Greater the star’s mass the faster it burns up its fuel
& the shorter the time it will be a main sequence star
 Some stars spend 90% of life as main sequence star
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Red Giant: star is running out of hydrogen fuel, cools,
gets bigger and becomes more luminous
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Planetary nebula: expanding shell of gases expelled into
space
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Helium flash occurs at red giant stage that many only last a few
minutes/seconds, star shrinks briefly than resumes red giant
status
Gases keep expanding until they dissipate in interstellar space
Core star left, but center becomes white dwarf.
White dwarf: small star (about size of Earth), super
dense, very high temperatures.
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Cools over billions of years to become black dwarf
Some can become supernova
2nd Path: stars 8 – 25 solar masses
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Main sequence: much shorter than for smaller stars, more
fuel but consumed at a faster rate
Red Supergiant: larger and more luminous
Supernova: star that blows off its outer shell into
interstellar space, luminosity soars & may outshine entire
galaxy
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Estimates show 1 supernova per galaxy every 25-100 years…we
have never observed a supernova in our galaxy with a telescope
Neutron Star: small (about size of large city), compact
stars
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Can give rise to pulsars – rapidly rotating stars that give off
pulses of energy
3rd Path: stars 25 – 130 solar masses
 Main Sequence: consume fuel at a much faster
rate than any of the previous stars
 Red Supergiant: similar to red supergiants for path
2
 Supernova: referred to as Type II supernova for
paths 2 and 3
 Black Hole: density so high that escape velocity
of star becomes equal to the speed of light, so
even light cannot escape