The Moving Sky

1
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

2
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.

3
Plate Tectonics

• Theory of continental drift (1924)
• Crustouter 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.

4
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 Earths surface
  temperature would be 13o. Burning of fossil
  fuels raises the temperature by 0.5o per century.

5
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.

6
Our Moon (I)

• With its radius about a quarter of the Earth
  radius, our Moon is the largest relative to the
  parent except Plutos 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.

7
Our Moon (II)
8
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).

9
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 Earths spin slows down
  and the lunar rotation is accelerated. Moons
  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.

10
Phases of Our Moon
sunlight
half Moon
Earth
full Moon
Moon
Moon phases are related to the shape of the
lighted part, as seen from the observation point
on Earth.
11
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.

12
The Terrestrial Planets Mercury

• Radius2,439km, revolution88d, spin59d.
• 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 day59 Earth days
• Observations Mariner 10 (1974).

13
The Terrestrial Planets Venus

• Radius6,052km, revolution225d, spin243d.
• 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)

14
Venus
15
The Terrestrial Planets Mars

• Radius3,200km, revolution687d, spin24h37m,
  same axis tilt as Earth.
• Mars is the least dense of the terrestrial
  planets core contains iron and iron sulfide no
  magnetic field. Schiaparellis 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
  Earths 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.

16
Mars
17
Mars Surface

• Mars Signature
• Dusty redish soil (the red planet)
• - The most similar to Earth

18
Mars Moons

• Phobos (R13.5km) and Deimos (R7.5km).
  They are captured asteroids.

Phobos