Download October 2010

Welcome to
Starry Monday at Otterbein
Astronomy Lecture Series
-every first Monday of the monthOctober 5, 2010
Dr. Uwe Trittmann
Today’s Topics
• Close Encounter with Jupiter
• The Night Sky in October
Observing Planets
• Inner Planets: closer to sun than Earth
– Mercury & Venus
– Always close to sun in the sky
• Outer Planets: further from sun than Earth
– Mars, Jupiter, Saturn, Uranus, Neptune, Pluto
– Best viewing when opposite of sun in the sky
Inner Planets
superior conjunction
Inner planet
eastern
elongation
western
elongation
inferior conjunction
Earth
Outer Planets
quadrature
conjunction
Earth
quadrature
Outer planet
opposition
Close Outer Planet
(Mars)
Size of planet
varies a lot as
Earth moves
Earth
Outer planet
Far-Out Planet
(e.g. Jupiter)
Earth
Size of planet
varies little as
Earth moves
Outer planet
Jupiter
•
•
•
•
Color: yellowish-white
Brightness: up to –2.9m
Size: up to 50”
When to observe: most of the year, except
for some months around conjunction
• Difficulty: easy, moons visible in binoculars
Jupiter & Moons
General Features of Jupiter
• Largest planet
• Low density
– Primarily ball of light
gases compressed by
gravity
•
•
•
•
•
Fastest rotation
No seasons
Has Rings
63 Moons
1/1000 mass of sun,
320x Earth
Jupiter’s Orbit
• Average distance from Sun: 779 mill. km =
5.2 A.U.
• Eccentricity: 0.0488
• Closest to Sun: 741 mill. km
• Farthest from Sun: 817 mill. km
• Jupiter Year = 11.86 Earth years
Kepler’s First Law
The orbits of the planets are ellipses, with
the Sun at one focus
Ellipses
a = “semimajor axis”; e = “eccentricity”
Kepler’s Second Law
An imaginary line connecting the Sun to any planet sweeps
out equal areas of the ellipse in equal times
Kepler’s Third Law
The square of a planet’s orbital period is proportional to the cube of its
orbital semi-major axis:
P 2  a3
a
P
Planet Orbital Semi-Major Axis Orbital Period
Mercury
0.387
0.241
Venus
0.723
0.615
Earth
1.000
1.000
Mars
1.524
1.881
Jupiter
5.203
11.86
Saturn
9.539
29.46
Uranus
19.19
84.01
Neptune
30.06
164.8
Pluto
39.53
248.6
(A.U.)
(Earth years)
Eccentricity
0.206
0.007
0.017
0.093
0.048
0.056
0.046
0.010
0.248
P2/a3
1.002
1.001
1.000
1.000
0.999
1.000
0.999
1.000
1.001
Jupiter Opposition 2010
• Best since 1951, until 2022
• Distance: 3.9539 AU
• unexpected disappearance of Jupiter's South
Equatorial Belt (SEB) earlier this year
• SEB’s return is often impressive, with
dramatic storms erupting suddenly.
• Days or years before Jupiter looks normal
again
Jupiter’s Atmosphere
• Cloud bands parallel
to equator
• Great Red Spot
– First observed in
1664 by Robert
Hooke
Jupiter’s Atmosphere
• 86% Hydrogen, 14%
Helium; some methane,
water, ammonia
• Several layers of clouds:
ammonia, ammonium
hydrosulfide, water
• Colors mostly due to
compounds of sulfur
and phosphorus
Great Red Spot
• About twice
the diameter
of the Earth
• A hurricane
that is
hundreds of
years old!
GRS
• As seen by
Voyager 1,
1979
Jupiters’ Bands: Zones and Belts
• Belts: cool, dark, sinking
• Zones: warm, bright, rising
• Jovian weather mostly
circles the planet due to
high rotation rate
• Bands exhibit east–west
flow Great Red Spot lies
between regions of opposite
wind flow
Naming of Belts & Zones
• Tropical,
equatorial,
temperate
Zone/Belt
Jupiter Changes
Missing Belt!
Rotation
• About 9 hours for Jupiter and Saturn
• Differential rotation: rotation speed varies from point
to point on the “surfaces”
– Gaseous bodies with no solid surfaces!
– On Jupiter, the equatorial regions rotate 6 minutes slower
than polar regions
• Flattening of planet!
• Tilt of rotation axis:
– almost none – no seasons!
4 Galilean Moons + 59 others
4 Moons are Planet Size
Jupiter’s Galilean Moons
Io
• Jupiter’s
innermost
moon
• Size and mass
similar to our
moon
• Zips around
Jupiter in just 2
days
• The most volcanically
active object in the
solar system
– Heated by tidal friction
• Eruptions as high as
200 miles, may last for
months
Io
Europa
Europa might have
liquid water oceans
under the surface
 Life?
Ganymede
Largest Moon in
the solar system:
5260km diameter
Icy surface,
dark parts are
oldest
View through the Telescope
Comet Shoemaker-Levy 9
• HST image (1994); Earth added to show scale
Comet Shoemaker-Levy 9
Headed for Jupiter…
Impact on Jupiter
Space Probes
• Pioneer
– Jupiter and Saturn; early 70's
– First man-made object to leave solar system
• Voyager
– “Grand Tour” of Jupiter, Saturn, Uranus and Neptune
– Launched 1977; arrived 1979
• Galileo
– Launched in 1989 on space shuttle
– Boosted by gravitational assists from Earth and Venus
– Two-part spacecraft arrived late 1995
• Atmospheric probe entered Jupiter's atmosphere 12/7/95
• Orbiter the first permanent orbiter of outer planets
• Cassini
- arrived at Saturn 2004, Huygens probes Titan right now
Internal Structure
• Gas of increasing density and pressure
• On Jupiter and Saturn, conditions are such that
hydrogen becomes metallic; dense cores
• Uranus and Neptune probably have conducting slushy
layers
Magnetospheres
• Very strong – Jupiter's
extends past the orbit of
Saturn!
• Indicate the presence of
conducting cores
The Night Sky in October
• The sun is past autumn equinox -> longer nights!
• Autumn constellations are coming up: Cassiopeia,
Pegasus, Perseus, Andromeda, Pisces
 lots of open star clusters!
• Jupiter is visible most of the night
Moon Phases
• Today (Waning Crescent)
• 10 / 7 (New Moon)
• 10/ 14 (First Quarter Moon)
• 10 / 22 (Full Moon)
• 10/ 30 (Last Quarter)
Today
at
Noon
Sun at
meridian,
i.e.
exactly
south
10 PM
Typical
observing
hour,
early
October
Uranus
Neptune
Jupiter
SouthWest
High in the
sky:
The summer
triangle
Due
North
Big Dipper
points to the
north pole
High up – the
Autumn
Constellations
• W of
Cassiopeia
• Big Square
of Pegasus
• Andromeda
Galaxy
Andromeda
Galaxy
• “PR” Foto
• Actual look
East
Perseus and
Auriga
with Plejades
and the
Double
Cluster
Greek
Mythology in
the Sky
South 2006
• Planets
– Uranus
– Neptune
• Zodiac:
– Capricorn
– Aquarius
South –
2007
• Planets
– Uranus
– Neptune
• Zodiac:
– Capricorn
– Aquarius
South –
2008
• Planets
– Uranus
– Neptune
• Zodiac:
– Capricorn
– Aquarius
South –
2009
• Planets
– Uranus
– Neptune
• Zodiac:
– Capricorn
– Aquarius
South –
2010
• Planets
– Uranus
– Neptune
• Zodiac:
– Capricorn
– Aquarius
Mark your Calendars!
• Next Starry Monday: November 1, 2010, 7 pm
(this is a Monday
• Web pages:
– http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.)
– http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)
)