AstronomyThe 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

Light Year Parsec

Distance between the Earth and the Sun

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/new-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