ASTR 100 Midterm

Basics scientific notation for distances
Earth-Sun distance = 93 million miles = 8.3 light minutes = 1 AU
Celestial Spheres & Motions of Stars
Zenith- point on celestial sphere directly overhead
Nadir- point on celestial sphere directly below
Celestial poles- either of two points at which extensions of earth’s axis intersect celestial sphere
Circumpolar stars- stars that never set at a given latitude; all stars between Polaris and northern horizon
Diurnal motion of stars
Means daily
Stars appear to move around sky every 24 hours because of rotation of earth
Constellations
Apparent groupings of stars
Move relative to one another
Constellations become distorted and morphed over hundreds of thousands of years
Seasons and Precessions
Sun changes position relative to constellations of zodiac
Constellations shift 1 degree per day
Earth rotates with fixed 23 ½ degree tilt
Zodiac constellations
Pisces – fish
Aria – ram
Taurus – bull
Gemini – twins
Cancer – crab
Leo – lion
Virgo – virgin
Libra- balance
Scorpius – scorpion
Sagittarius – archer
Capricorn – goat
Aquarius – water carrier
Sun moves along eliptic, enters new constellation every month
Twice per year sun is on celestial equator
Once per year sun is at extreme northern point
Once per year sun is at extreme southern point
March 22- vernal equinox
June 21- summer solstice
Sept 22- autumnal equinox
Dec 22- winter solstice
Cause of seasons
Length of day changes
10 hours during winter
14 hours during summer
Altitude of sun controls insolation
Distance between sun and earth holds no effect
Phases of the Moon and Eclipses
Sidereal and synodic periods
Moon shines by reflected light
50% of moon always bright
50% always dark
Phases determined by fraction visible
Full and new moon; 1st quarter and 3rd quarter; gibbous and crescent; waxing and waning
Eclipse
umbra- darkest region (of shadow) penumbra- “half-dark” region (of shadow) lunar eclipse- full moon gets dark solar eclipse- sun blocked by new moon total eclipse- partial eclipse annular eclipse- new moon doesn’t block sun but leaves outer bright ring
Greek & Renaissance Astronomers
Aristotle – 350 BC
Round Earth
4 basic elements (earth water fire air)
Earth fixed at center of universe
Adopted as truth by Holy Roman Empire
Hipparchus – 140 BC
Catalogued stars, made first atlas, estimated brightness of stars
Discovered precession
Predicted eclipses
Used parallax (relative motion of foreground object relative to more distant fixed object) to determine distance to moon
Ptolemy – 140 AD
Worked at Great Library at Alexandria
Adopted Hipparchus’ star catalog
Wrote Almagest
Predicted paths of sun, moon, and planets for more than 1000 years
Earth-centered cosmology with epicycles
Copernicus – 1543
First to propose and support with observations a heliocentric theory
Tycho Brahe – 1600
Determined accurate positions of stars
Built observatories on Island of Hven
Saw no parallax for comet and nova
Tracked position of all planets
Johannes Kepler – 1610
Orbits of planets are ellipses
Planets sweep out equal area in equal time
Period squared = distance cubed P2=a3
Galileo – 1610
Conducted physics experiments
“Leaning Tower of Pisa” experiment
Studied friction
Understood path of cannon balls
Built telescopes
Discoveries
Mountains, craters, and seas on moon
Sunspots on sun
Phases and changing diameters of Venus
Moons of Jupiter and motion
Milky Way consists of crowded star fields
Isaac Newton (1666)
Studied nature of light, motion, optics, astronomy
First to understand tides
Invented calculus
Made first reflecting telescope
Studied alchemy & religious chronology
Member of Parliament and Master of mInt
Refused to publish work
Laws
An object in motion remains in motion until acted upon by external force (inertia)
Force = mass * acceleration
For every force this is an equal and opposite force
Universal gravitation

G = gravitational constant; 6.67 X 10-11 Newtons m2/kg2
Nature of Light λ = wavelength (from one crest to the next) ν = frequency (how fast do crests arrive) c = speed of light 2.995 x 108 m/s
186,000 miles/s = 7.5 times around Earth/s c = λ ν
E = h ν (energy is proportional to frequency) h= Planck’s constant = 6.67 x 10-34 Joule sec
Light, Telescopes, & Optics important functions of telescopes collect light resolve fine angular details magnify image of object objective diameter/eyepiece diameter absorption of rays
Gamma rays – absorbed
X-rays – absorbed
UV – mostly absorbed
Visible (blue, green, red) – transmitted
Infrared – selective absorbed, some transmitted
Microwave – absorbed
Radio – transmitted
Spectrographs, Radio Telescopes, & Space Telescopes
CCD
Charge Coupled Device
Wafer of silicon with ion implants to define pixels
Pixels = picture elements
Photons hit surface create image by separating electrons from parent atom
Electrons moved across silicon surface, sent to “horizontal register,” sent out to computer memory
Diffraction limit of telescope
2 x 105 λ / D
Space telescopes
Hubble – visible wavelengths
Spitzer – infrared
Chandra – x-ray
Spectra in Astronomy
Wien’s law: λmax = constant / T
Electrons
Orbit nucleus
Confined to specific orbitals determined by electron’s wavelength
Jump from one orbital to another
Always seek ground state
Precise amount of energy required to force transition
Can escape if given excess of energy; atom becomes ionized
Doppler shift
Speed is proportional to frequency change
Δλ / λ = Δν / ν = v / c
Solar System Overview & Other Planetary Systems
Mean density = total mass/total volume
Models
Concepts not fully developed
Start with disk of gas and dust orbiting around proto-Sun
Condensation process in disk studied by chemistry of meteorites
Earth
Mass: 1/3,000,000 of Sun
Mean density: 5520 kg/m3
Atmosphere: 78% N; 21% oxygen; 1% other
Albedo: 37%
One moon
Modest magnetic field
Tidals created by earth and moon
Friction between water and ocean floors cause tidal bulge to lead
Moon accelerated by bulge causing it to move away from earth at 3.8 cm per year
Active crust = plate tectonics
Moon
Mass: 1/81 Earth
Radius: ¼ Earth
Mean density: 3300 kg/m
Albedo: 12%
No atmosphere
Weak magnetic field in past, none now
Surface
Mare (maria in plural)- circular dark lava-filled basins; basalt = rock type
Highlands = bright mountain areas, breccias
Craters formed by impacts
Interior
Very small iron core
Very thick mantle of rocky rubble
Mercury & Venus
Mercury
Mass: 5.5% Earth
Diameter: 38% Earth
Mean density: 5430 kg/m3
Albedo: 12%
Weak magnetic field
Year = 88 days
Day = 59 Earth days
No moons
Surface resembles moon; has open plains
No erosion
Interior
Iron and nickel, extends out to 85% of radius
Small magnetic field
Venus
Sister planet of Earth
Mass: 81% of Earth
Radius: 95% of Earth
Mean density: 5240 kg/m3
Albedo: 65%
No magnetic field
Year: 225 earth days
Day: 243 Earth days
Atmosphere
96% CO2 4% N2
Clouds are sulfuric acid
Rains sulfuric acid, liquid evaporates
Sulfur comes from volcanic activity
Density is 90x Earth’s atmosphere
Surface
Many volcanic features, few impact craters
Lava flow cover 80% of surface
No plate tectonics
Mars
Mass: 11% earth
Diameter: 53% earth
Mean density: 3950 kg/m3
Albedo: 15%
Weak magnetic field
Year: 687 days
Day: 24 ½ hours
Axis tilt: 25 degrees
Two moons: Phobos & Deimos
Life
Mars rock landing in Antarctica shows fossil evidence of bacteria-like life forms
Atmosphere
Thin atmosphere; 0.6% Earth
95% CO2
Clouds of water
Northern hemisphere once filled with water, disappeared
Exploration
Approx. 40 space probes sent, ½ worked
Viking landers 1976 search for life
Mariner 4, 6, 7, 9
Surface rovers: Sojourner, Spirit & Opportunity, Curiosity
Phoenix Lander: 2008 data from polar regions
Mars Reconnaissance Orbiter: high res pictures
Surface
Northern hemisphere
Smooth, many volcanic features and evidence of water
Olympus Mons = largest mountain in solar system
Tharsis Ridge
Marineris Valley = 4000 km long
Southern hemisphere
Highlands with old cratered areas
Gas Giant Planets & Jupiter
Gas giant planets
More massive than Earth
No solid surface
Numerous moons
Significant magnetic field
Each planet has ring
Jupiter
Mass: 318 X earth
Diameter: 11.2 X earth
Mean density: 1330 kg/m3
Albedo: 0.52
Magnetic field: 14 X earth
Year: 11.86 Earth years
Day: 9 h 50 min
Axis tilt: 3 degrees
67 moons
Atmosphere
Cloud tops: 71% hydrogen, 24% helium, 5% everything else
Cloud composition
Ammonia
Water
Ammonium hydrosulfide
Other unknown molecules
Interior
Rocky core
Layer of ices: water, methane, ammonia ice
Very thick layer of helium mixed with liquid metallic hydrogen
Moons
Synchrotron radiation
Needs a magnetic field and charged particles
Charged particles come from Sun
4 small inner moons - prograde
4 large Galilean moons – prograde
Io – 1.8 day orbital period
Mass = 1.22 X moon
Diameter = 1.04 X moon
Mean density = 1.07 X moon
Iron core
Most active-volcanic object in solar system
Europa – 3.6 day orbital period
Mass = 0.65 moon
Diameter = 0.90 moon
Mean density = 0.89 moon
Possible ocean below ice crust that could support life
Ganymede – 7.2 day orbital period
Mass =2 X moon
Diameter = 1.5 X moon
Density = 1940 kg/m3
Callisto – 16.7 day orbital period
Resembles Ganymede
6 small outer moons - prograde
53 small outer moons – retrograde
Saturn
Mass: 95 x Earth
Diameter: 9.4 x Earth
Mean Density = 690 kg/m3
Albedo = 0.47
Magnetic Field: 2/3 Earth
Year = 29.5 Earth years
Day = 10 h 14 m
Axis tilt = 27o
62 Moons (only 7 are spherical
15 years- see top of rings
15 years- see bottom of rings
Moon
Titan
Second to Ganymede in size
Only moon with significant atmosphere
Density 4 X earth’s
90% nitrogen
Lakes of methane and ethane larger than Lake Superior
Hazy fog (smog) obscures surface
Enceladus
1/8 diameter of earth’s moon; ocean of water under ice surface
Hyperion
Same diameter, 1/100 mass of Enceladus
Rings
Consists of billions of individual particles orbiting Saturn
Particle sizes range from 10 m in diameter to dust with avg size of 1 cm
Ice or ice-coated particles
10 m; total ring width = 380,000 km
Named with capital letters A-G
D C B A G F E
Largest ring particles found in A ring
Cassini Division (separates B & A)
Encke Division (separates A & G)
Interior
Resembles Jupiter
Rocky material about same size of Jupiter’s
Layer of ices: water, methane, and ammonia ice
Very thick layer of helium mixed with liquid metallic hydrogen
On top is helium and molecular hydrogen
Atmosphere
Resembles Jupiter’s
Winds are higher
Uranus, Neptune, & Dwarf Planets Including Pluto