WC8

The Moving Sky: 

The Moving Sky Earth movement: spin(24h), revolution(365.2422d) The 23.4o tilt/declination and the seasons Motion of the Moon (27.32d) Longitude and time Calendars: Julian(45 BC), Gregorian (1582 AD) Planets orbits and speed: Mercury 48km/s, Earth 29.8 km.s, Pluto 5km/s. Comets: high eccentricity and variable speed

Earth Structure: 

Earth Structure Earth is more massive than Mars or Venus, has 70% of surface covered with water. Density of material doubles as one goes to its deeper layers. Layers: The outer crust has 10-50km (5-10km in ocean beds) A mantle of denser rock has 2,900km The outer core (iron, nickel) is liquid and has 2,200km The inner core is solid and has 1,300km. Temperature over 5000o fueled by radioactive disintegrations. Geophysicists determine all this from the study of seismic waves.

Plate Tectonics: 

Plate Tectonics Theory of continental drift (1924) Crust+outer mantle(lithosphere) which is rigid and brittle Eight large (plus many small) plates flow very slowly on top of the inner mantle At boundaries magma rises and creates new crust structures (ex. mid-Atlantic ridge). In addition earthquakes and chains of volcanoes. Some short-lived volcanoes appeared in hot spots in the middle of a plate (ex. Hawaii islands). Earth surface rocks vary in age corresponding to a very dynamic history. Water and the wind also shape them.

Earth Atmosphere: 

Earth Atmosphere Composition: nitrogen (78%), oxygen(21%) Oxygen is highly reactive and must be replenished – photosynthesis uses CO2 to produce oxygen CO2 (0.03%) is mainly in limestone and ocean. Like water, CO2 contributes to the greenhouse effect, which keeps the temperature at an average of 17o. Without the atmosphere Earth’s surface temperature would be –13o. Burning of fossil fuels raises the temperature by 0.5o per century.

Atmospheric Layers: 

Atmospheric Layers To 10km troposphere - temperature 17o to –53o 10-50km stratosphere – temperature raises to -3o because ozone (O3) absorbs UV light. 50-80km mesosphere – temperature drops to –68o 80-150km thermosphere/ionosphere – temperature raises to 800-2000o because of atomic and molecular processes with UV and X rays; ions and electrons influence radio communications To 70,000km magnetosphere – Van Allen belts deflect the solar wind and cause auroras at the poles.

Our Moon (I): 

Our Moon (I) With its radius about a quarter of the Earth radius, our Moon is the largest relative to the parent except Pluto’s Charon. Elliptical motion with an average distance of 1.2 light-seconds (or 384,400km) Surface with cratered highlands (85%) and “seas”(15%). Both craters and seas were formed by meteor impact. The dark-colored seas correspond to magma spilled after impacts. Water ice is mixed with rocks at the two poles Most likely our Moon was formed through an impact between Earth and a similar size body. The same impact might be the origin of the tilt in the Earth axis.

Our Moon (II): 

Our Moon (II)

Our Moon Structure: 

Our Moon Structure No atmosphere (too small to keep it) 1-20m lunar soil (pulverized rocks) Below the soil about 65km of lunar crust Below the crust about 1,400km of a mantle of denser rock The lower part of the mantle (at about 800km) is partly molten. Minor seismic events are generated at that level. The center might contain an iron-rich core (350km in radius).

The Earth-Moon System : 

The Earth-Moon System Why do we see various lunar shapes ? It is related to the relative positions of Earth, Moon and Sun. Ocean tides: As a result Earth’s spin slows down and the lunar rotation is accelerated. Moon’s spin also slowed down and now the fact that its spin is synchronized with its revolution results in the fact that the same hemisphere is shown to Earth. Solar/Lunar Eclipses: a solar eclipse is max.7.5 mins. Lunar eclipses are less frequent than solar eclipses but are seen from the whole hemisphere. Max number of eclipses per year is seven.

Phases of Our Moon: 

Phases of Our Moon sunlight Earth Moon Moon phases are related to the shape of the lighted part, as seen from the observation point on Earth. full Moon half Moon

Other Planets: 

Other Planets The terrestrial planets - Mercury, Venus, Earth and Mars - are relatively small, dense with similar composition and with solid surfaces. The jovian (giant) planets - Jupiter, Saturn, Uranus and Neptune - are much larger than Earth. Their structure is either a hydrogen-helium gas, or a solid icy structure. Pluto is a small planet made out of rock and ice.

The Terrestrial Planets: Mercury: 

The Terrestrial Planets: Mercury Radius=2,439km, revolution=88d, spin=59d. 70% iron and 30% rock, but small magnetic field implying that most iron is solid. Wrinkles suggest past magma flow; impact craters. Almost no atmosphere. Mercury Signature: Day temperature up to 425oC, Night temperature -173oC But its “day”=59 Earth days Observations: Mariner 10 (1974).

The Terrestrial Planets: Venus: 

The Terrestrial Planets: Venus Radius=6,052km, revolution=225d, spin=243d. Structure similar to Earth. Volcanic activity older than on Earth. Atmosphere contains 96.5% carbon dioxide and 3.5% nitrogen with clouds of sulphuric acid between 5-70km altitude. Venus Signature The greenhouse effect maintains a constant 480oC. It also makes Venus brighter than stars. Water and carbon dioxide history different from Earth because of distance to the Sun. Observations: radar-Mariner 2 (1962), landed - Venera 7 (1970) 9,10 (1975), radar - Pioneer 12 (1978), Magellan (1994)

Venus: 

Venus

The Terrestrial Planets: Mars: 

The Terrestrial Planets: Mars Radius=3,200km, revolution=687d, spin=24h37m, same axis tilt as Earth. Mars is the least dense of the terrestrial planets; core contains iron and iron sulfide; no magnetic field. Schiaparelli’s polar caps and canals (1877), dusty red soil (iron oxides), Olympus Mons volcano 25km altitude, Mariner valleys 8km depth, dyed-up river beds. Although the composition of the atmosphere is similar to Venus, its density is about half of Earth’s atmosphere and therefore there is no significant greenhouse effect; day 20oC and night -70oC; ice clouds, dust storms. Possibility of past life (Viking 1976, Antarctica meteorite 1996). Other missions: Mariner 4 (1965), Mars Pathfinder (1997) etc.

Mars: 

Mars

Mars Surface: 

Mars Surface Mars Signature: Dusty redish soil (the “red” planet) - The most similar to Earth

Mars Moons: 

Mars Moons Phobos (R=13.5km) and Deimos (R=7.5km). They are captured asteroids. Phobos