Exam 3 Flashcards
Terminator
Line separating dark and lighted area
Limb
The outside line of the moon
perigee
closest aproach
apogee
Farthest away
Libration
The oscillation of the moon due to the elliptical orbit.We can see about 59% of the moon due to Libration over the course of time
sidereal month
The Moon takes 27.3 days to go round the Earth
synodic month
it is 29. 5 days between consecutive full moons
Blue moon
second full moon in a single month
path of the moon in the sky?
east to west
Tilt of the moon.
The tilt of the moon’s orbital path to the earth’s is 5.2o. This is the reason why there is not an eclipse every month
Penumbra
Sun partially visible in a solar eclipse (annular)
Umbra
sun completely obscured, total eclipse seen
earth’s orbit around the sun
Perihelion = 147 Mkm in early January Aphelion = 152 Mkm in early July
Moon’s orbit around the Earth is elliptical
Perigee = 363,000km Apogee = 406,000km
Node
Point where the path of the Moon crosses the ecliptic
When the Sun and moon are at the same node
solar eclipse
When they are at opposite nodes
lunar eclipse
Solar eclipse season lasts
32 days
Lunar eclipse season lasts
22 days
Nodes every years
18.6
1 saros=
18 years + 11.33 days = 223 synodic = 242 draconic = 239 anomalistic and 6585.321 days = 223 lunar months = 19 eclipse years
For an eclipse in the same location
Earth rotates an extra 120 degrees because of the 1/3 day (needs 3 saros for eclipse)
Draconic month
time between twoSimilar nodes
Anomalistic month
time for the moon to move from perigee to perigee
Days of week named after
Planets
Planet =
wanderer
Elongation of Venus
– it is easy to see as Venus is the 3rdBrightest object in the sky – it is usually the first “star” to be seen in the sky after theSun sets
How to find synodic period
1/synodic period = |1/sidereal period - 1/sidereal period of earth|
How fast does the moon move
It moves an angular distance equal to its size in about an hour or about 13o a day
The sidereal period for Mercury and Venus
Mercury = 88 days Venus = 225 days
The Synodic period for Mercury and Venus
Mercury = 116 days Venus = 584 days
Retrograde
The planets appear to wander among the stars in alooping motion due to Kepler’s 3rd law
Hipparchus
The First true astronomer Tremendous mathematical insight Invented trigonometry First star catalogue discovered precession
Ptolemy
A Cosmos based on what had gone before Transformed Aristotle’s workinto a sophisticated model The Earth was stationary Universe was a celestial sphere Planets orbited the earthin a complex motion
Copernicus
Heliocentric model
Galileo (17th C)
Performed experiments to test his ideas
Tycho Brahe
Eccentric astronomer Very detailed observations of the sky – so accuratewere his observations that scientists travelled fromall over Europe to his observatory He was obsessed with accuracy Observed conjunction of Jupiter and Saturn in1563 Alfonsine tables (Ptolemaic – 1251) error of amonth in the date Prutenic tables (Copnernican – 1551) error oftwo days in the date Showed that comets travelled through spacenot the atmosphere Confirmed the changing nature of the universewhen he observed a supernova in 1572. he provedthat it was in the realm of the stars
Eccentricity
(distance from focals to center)/(Semi-major axis)e = 0 => circle0 Ellipsee > 1 hyperbola
Kepler’s 1st law
Orbits are ellipses; mercury is the most elliptical
Kepler’s 2nd Law
A line connecting a planet to the sun sweeps out equal areas in equal time When the planet is closest to sun (perihelion) it moves fastest When it is furthest from the sun (aphelion ) it moves slowest
Kepler’s 3rd Law
The square of the planet’s orbital period is proportional to the cube of its distance from sun(T1/T2)^2 = (R1/R2)^3
Discovery of Uranus - 1781
Galileo saw it in 1613 - when he recorded itand another star on two different dates and noted that the distance between them had changed Other astronomers recorded it - but thoughtit was a star because of its size – 3’’ across! English astronomer William Hershel viewed it through his homemade 6” - thought it was a cometGalileo’s notes Observed it over a period of time and realised it was a new planet It is just visible to the naked eye and its small size (4.1” at opposition) make it hard to notice Was made court astronomer to king George 3rd for his discovery – tried originally to name it George’s planet
Discovery of Neptune
Was discovered in 1846 Problems with orbit of Uranus Conclusion was that another unseen planet was affecting its orbit Two mathematicians independently predicted its mass and orbit and therefore itsexpected position John Couch Adams (England) 1845 Urbain Leverrier (France) 1846 The discovery almost caused a diplomatic incidentbetween the two countries – partly because of George Airy – astronomer royal Was observed by a German – Johann Galle The planet is not visible to the naked eye and at an angular size of only 2.4” at opposition it is hard to distinguish it from the background starsBritain and France argued over who was pre-eminent in the discovery AdamsandLeVerriertookno part in the controversy and actually became good friends because of it Neptunewasactually discovered pretty close to where the two men predicted it would be
Discovery of Pluto
Was discovered in 1930 - problems with Neptune’s orbit Percival Lowell (Martian canal fame) Predicted its position and searched in vane for it Died before it was found Was discovered from observations of photographic plates by Clyde Tombaugh at the Lowell observatory in Flagstaff Arizona Two new moons discovered, Nix and Hydra, very recently
Age of the solar system
About 1/3 age of universeFormation of the Solar system The solar system is believed to be about 4.5 billion years old At turn of 20thC it was thought it could be only 20 million (Kelvin’s estimate) Method uses radioactive decay (idea by Rutherford) of Uranium into Lead (Clair Patterson used ancient rocks – meteorites – 7 years to complete) Earth age 4,550 million years +/- 70 other studies confirm age
Collapsing cloud of gas and dust
Solar system started off as a massive cloud (Nebula) of gas anddust (first proposed by Descartes 17th C) maybe 1Ly across Due to external forces (collision, supernova) cloud begins tocollapse under gravity. As it collapses it becomes denser and hotter – hot enough for a star to form in the centre (see later notes) planets form in outer regionsCollapsing cloud will naturally spin Due to conservation of angular momentum (first proposed by Laplace18th C) nebula spin will increase as it collapses Nebula’s shape changes as it collapses to form a flattened disk – ascentrifugal forces in direction of rotation oppose collapse Explains orbital aspect of the planets (orbit in same direction and same plane (ex. Pluto) and rotational in same sense (ex. Venus, Uranus and Pluto)
Protoplanetary disk around HL Tau
HL Tau only 100,000 yrs old – 520 Ly away Youngest forming planet ever seen! A ball of gas and dust forming About 14 times mass of Jupiter
The Sun
– the nearest star Distance = 93 million miles away 8 1/3 minutes at speed of light Massive in comparison to earth, 240,000 timesbigger !! Uses 4,500 million tons of Hydrogen everysecond as fuel. Considered to be around 4,500 million years old(half way through its lifetime) More about the Sun in AST2004!
Mercury
Slightly larger than the moon and similar looks Hard to see from earth due to proximity to sun Daily temperature range +400oC - -180oC Length of day – 59 days length of year 88 days – 2:3 ratio Covered with thousands of craters indicating a violent past Has a weak magnetic field indicating an iron core Mariner is the only space probe to visit Mercury Mercury messenger launched 2004 arrives 2011 via Venus, Earth
Venus
- Almost a twin of the earth Similar size, density and chemical composition Now very different from the earth Dead, hostile, fiery inferno - Several probes dead! Pressure 90atm at surface - thick clouds of CO2 A day (243 days) is longer than a year (225 days)and spins “wrong way” – Earth responsible – showsexactly the same face upon closest approach to earth Clouds of Sulphuric acid Phantom rain! Surface temperature nearly 500oC Runaway greenhouse effect A lot of volcanic activity
Mars
2nd most hospitable place for life in solar system Water once flowed over its surface Length of day is similar to earth’s and it hasseasons like the earth Has valleys (Valles marineris – 90 miles wideand 2 miles deep) Largest volcano in solar system – Olympus mons– 15 ½ miles high MarsSpirit roverPhobos Surface soil is high in iron – rusty Debate as to whether life onceexisted Two small moons – Phobosand Deimos USA committed to sending amission to Mars
Jupiter
Largest planet in solar system – more than twice themass of all the other planets put together Has storms bigger than earth! Day is only 10 hrs long, year is 12 years –fast rotation affected shape - 6% wider at the equatorthan at the poles Composition is primarily H and He due to stronggravity (similar to the sun) Great red spot is a storm lastedfor at least 300 yrs Has a very strong magnetic fielddue to “metallic” H in the core,surrounded by liquid H
Saturn
Takes 30 years to go around the sun. Has 46 moons! Has the biggest moon (Titan) in the solar system– like the earth in deep freeze. Rings seen from different orientations as it orbitsthe sun (30yr orbit) Saturn is least densest planet – theoreticallywould float on water Rings consist of particles – mostly water icefrom mm to 10’s of metres
Uranus
Massive axial tilt (98o) means seasons on Uranuslast 21years each Has a rocky core and with H and He atmosphereand some methane (gives rise to blue colour) 27 moons some of which,Mirandaindicate violent past (20km deep cliff) Uranus Faint ring system detectedusing stellar occultation Actually spins faster at thepoles than the equator
Neptune
The most distant of the gas giants – 30AU fromthe sun – took 12 yrs for voyager 2 to get therefrom earth Similar to Uranus in size and composition (moremethane - bluer) but slightly more massive Neptune Interior of the planet rotates fasterthan the atmosphere! Has storms similar to that of Jupiter Winds blow at speeds up to900mph in the upper atmosphere The moon Triton has nitrogengeysers on the surface Has a faint ring system
Pluto
Pluto is so far away – no good pictures Orbital plane lies 19o off the ecliptic A tiny world – only the size of the moon On Pluto a year lasts for 248 years! Most eccentric orbit (sometimes Neptune is further away from sun) The Sun would only appear as a bright star in the sky Surface temp only 50ok! New Horizons probe launched 2006 – 10 year journey
