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Astronomy
The Study of the Universe
Astronomy
• Azimuth, Altitude, Right Ascension,
Declination
• Constellations
• Distances in Space
• Parallax distortion
• Spectra (absorption and emission)
• Basic properties of stars
– Diameter, mass, brightness, energy
output, surface temperature and
composition
Measuring Star Positions from Earth
Method 1:
• Azimuth: the angular distance along the
horizon to the location of an object (usually
starting from the North pole and moving East;
0-360˚)
• Altitude: the distance an object appears to be
above the horizon. (0-90˚)
Method 1 is dependent on the location of an
observer on Earth
Measuring Star Positions from Earth
Method 2: (more common because of standardized coordinates)
• Right Ascension (α) :
– measured in hours (since the celestial equator is divided
into 24 equal portions)
– Each hour is divided into 60 equal minutes
– 0 hour is the vernal/March equinox
– Analogous to longitude
• Declination (δ):
– At the celestial equator (0˚), the north pole (+90˚), the
south pole (-90˚)
– Analogous to latitude
Will this system work forever?
NO! What does this mean about astrology?
Constellations
• Prominent luminous objects in the sky that
seem to form patterns to observers on Earth
• The International Astronomical Union (IAU)
recognizes 88 constellations
Andromeda · Antlia · Apus · Aquarius · Aquila · Ara · Aries · Auriga · Boötes · Caelum · Camelopardalis · Cancer · Canes Venatici · Canis Major · Canis Minor ·
Capricornus · Carina · Cassiopeia · Centaurus · Cepheus · Cetus · Chamaeleon · Circinus · Columba · Coma Berenices · Corona Australis · Corona Borealis ·
Corvus · Crater · Crux · Cygnus · Delphinus · Dorado · Draco · Equuleus · Eridanus · Fornax · Gemini · Grus · Hercules · Horologium · Hydra · Hydrus · Indus ·
Lacerta · Leo · Leo Minor · Lepus · Libra · Lupus · Lynx · Lyra · Mensa · Microscopium · Monoceros · Musca · Norma · Octans · Ophiuchus · Orion · Pavo ·
Pegasus · Perseus · Phoenix · Pictor · Pisces · Piscis Austrinus · Puppis · Pyxis · Reticulum · Sagitta · Sagittarius · Scorpius · Sculptor · Scutum · Serpens · Sextans
· Taurus · Telescopium · Triangulum · Triangulum Australe · Tucana · Ursa Major · Ursa Minor · Vela · Virgo · Volans · Vulpecula
•Throughout history different cultures have
noticed and given meaning to constellations
Ursa Major (Big Dipper)
• The Navajo (American Natives) describe Ursa
Major as the Great Bear.
Ursa Minor (Little Dipper)
• Commonly visualized as a baby bear with an
unusually long tail (from being spun around the
Earth)
Ursa Minor (Little Dipper)
• Discovered by Claudius Ptolemaeus (Ptolemy)
•At the end of the 'handle' lies Polaris (North
Star)
Ursa Major and Ursa Minor
• Artemis, the moon goddess and goddess of the hunt, always had hunting
companions with her when she went on the hunt. One such companion was
Callisto, a beautiful young maiden. One day Zeus passed by a woodland cove and
spied the sleeping Callisto. Zeus disguised himself as Apollo and made Callisto his
lover. They had a child named Arcas. Of course Zeus knew that both Hera, his wife,
and Artemis would be angry with Callisto so to protect her he turned her into a
bear to keep her hidden from Artemis and Hera. One day, Arcas was hunting and he
came across a great bear. He was just about to shoot his arrow when Zeus
intervened and changed him into a little bear so that Arcas could know who the
great bear really was. Zeus then transported the two bears to the heavens so that
they would be protected from the wrath of the angry goddesses. However, Hera
was unhappy that Callisto and her son were shining so brightly in the heavens so
she asked the ocean god to prevent them from ever bathing in the ocean waters.
And so, according to this story, that is why the two bears are forced to circle the
heavens while the other constellations are allowed to dip below the horizon and
bathe in the immortal waters every night.
Polaris aka North Star aka Pole star
• The brightest star in
the Ursa Minor
constellation
• 430 light years from
earth
• Actually a multiple
star system
The
constellation
of Orion
(useful in
finding other
stars)
Sirius
• The brightest star in
Earth’s sky
•Part of Canis Major
(the dog star)
Distances in Space
Astronomical
Unit
Distance
between the
Earth and the
Sun
Light Year
Parsec
Distance light
travels in one
Earth-year
‘Parallax of one
second’
1/3600 of 1
degree
149 598 000 km 9.46 x 1012 km
3.085 x 1013 km
Parallax Distortion
• The difference in the apparent position of an
object viewed from two different lines of
sight.
• Objects closer to an observer seem to
undergo more parallax distortion than objects
far away
http://www.astro.ubc.ca/~scharein/a311/Sim/n
ew-parallax/Parallax.html
Absorption and Emission Spectra / aka
Kirchoff’s Law of Thermal Radiation
1) Continuous Spectrum
– No breaks
– Produced by glowing gas, liquid or solid
2) Emission Spectrum
– Discrete energies produced as atoms transition
between energy levels
– Produced through non-compressed gas
3) Absorption Spectrum
– Discrete energies are shown as dark lines
indicating particular wavelengths of light
Basic Properties of Stars
•
•
•
•
•
•
Diameter,
Mass,
Brightness,
Energy output,
Surface temperature and
Composition
Brightness (magnitude)
• Apparent magnitude refers to a relative measure of
brightness originally created by ancient Greeks
• A difference of 5 magnitudes corresponds to a factor of
100 in brightness.
• 1+ indicates the brightest star and 6 represents the faintest
• Absolute magnitude standardizes brightness by
refering to brightness at a distance of 10 parsecs
• Can only be calculated when the star distance is known
Energy Output (Luminosity)
• Energy output / second
• Apparent magnitude and distance must be known
• EX. Our Sun’s luminosity is
~385 000 000 000 000 000 000 000 000 W (Joules per
second)
• Extremely variable
Wavelength Shift (The Doppler Effect)
• Stars and star systems moving toward an observer
seem to emit relatively shorter wavelengths of light
(blue-shift)
• Stars and star systems moving away from an
observer seem to emit relatively long wavelengths of
light (red-shift)
Hertzsprung-Russell diagram
• H-R Diagram
• Used to relate a star’s luminosity, surface
temperature and spectral type (O, B, A, F, G, K, M)
Homework
• Hertzsprung Russell Diagram
• Data Analysis Lab on page 835
• GeoLab on page 853
– Identify the unknown elements
– Complete Analyze and Conclude Q:1-3