Download October 2007

Welcome to
Starry Monday at Otterbein
Astronomy Lecture Series
-every first Monday of the monthOctober 1, 2007
Dr. Uwe Trittmann
Today’s Topics
• Atmospheric Histories – Or: Is the
Greenhouse Effect positive or
negative?
• The Night Sky in October
Feedback!
• Please write down suggestions/your interests on the
note pads provided
• If you would like to hear from us, please leave your
email / address
• To learn more about astronomy and physics at
Otterbein, please visit
– http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.)
– http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)
Obviously …
• No “Greenhouse Effect” without
greenhouse – need an atmosphere
• But: atmospheric histories possible without
atmosphere! (it could have vanished)
• “Positive” and “negative” have a colloquial
and a scientific meaning
Greenhouse Effect
• Earth absorbs energy
from the Sun and
heats up
• Earth re-radiates the
absorbed energy in
the form of infrared
radiation
• The infrared radiation
is absorbed by carbon
dioxide and water
vapor in the
atmosphere
Greenhouse Effect
• By “absorption” we
mean that the
radiation’s energy get
stored in the molecule
• The molecule has
now more energy,
corresponding to a
higher temperature
Positive, negative and runaway
Greenhouse Effects
• Positive greenhouse effect heats up a
surface from the temperature that it
normally would have
– Earth would be 74 F colder without it
• Cooling effects are sometimes called a
“negative” or “inverse” greenhouse effect
• Runaway greenhouse effects get stronger as
the temperature gets up, e.g. because this
releases more greenhouse gases
• If you like it cooler, a positive greenhouse effect could be
“negative” 
Overview: The Solar System
Contents of the Solar System
• Sun
• Planets – 9 known (now: 8)
– Mercury, Venus, Earth, Mars (“Terrestrials”)
– Jupiter, Saturn, Uranus, Neptune (“Jovians”)
– Pluto (a Kuiper Belt object; officially a “dwarf planet” )
• Natural satellites (moons) – over a hundred
• Asteroids and Meteoroids
– 6 known that are larger than 300 km across
– Largest, Ceres, is about 940 km in diameter
• Comets
• Rings
• Dust
Size matters: radii of the Planets
Typically:
larger radius
larger volume
larger mass
larger gravitational pull
The Terrestrial Planets
• Small, dense and rocky,
solid surface
Mercury
Mars
Venus
Earth
The Jovian Planets
• Large, made out of gas, and low density, no
solid surface
Saturn
Jupiter
Uranus
Neptune
All Planets were formed from the
same gas cloud at the same time
• Formation of the Solar
System from a rotating
cloud of gas and dust
• Dust helps cool the
nebula and acts as
seeds for the clumping
of matter
Why are the planets so
different?
Differences of the Planets explained
32ºF
Temperature and density of materials drop with distance to sun
Atmospheric Histories
• Primary atmosphere: “primordial” materials:
hydrogen, helium; plus: methane, ammonia
– Too light to “stick” to a planet unless it’s very big 
Jovian Planets
• Secondary atmosphere: water, CO2, SO2, …
– Outgassed from planet interiors, a result of volcanic
activity
• Tertiary atmosphere: changes due to biological
activities on surface
Current Atmospheres
• Mercury, Moon 
(and most moons),
asteroids: no
atmosphere!
• Note the soft edges of the
crater erosion without
atmosphere!
Venus’ current Atmosphere
• 96.5% CO2, 3.5% Nitrogen at 90 times Earth’s
atmospheric pressure; sulfuric acid clouds
View from Russian probe Venera 14 (1975)
Hothouse Venus: 870 °F – liquid lead!
Current Atmosphere of Earth
• 78% Nitrogen,
21% Oxygen,
1% Other
– Most “other” is
Argon!
• Troposphere –
region of weather
• Stratosphere –
stable and calm
• Ionosphere –
gases charged by
interaction with
radiation from
space
Ozone Layer (O3)
• Absorbs most UV
radiation from the
Sun
• Hole over
Antarctic
– Chlorofluorocarbons
(CFC’s) – released by
spray cans,
refrigerators
• Ozone at ground
level is a pollutant!
Mars’ current atmosphere
• 95% CO2, 3% Nitrogen at less than 1% of
Earth’s atmospheric pressure
Martian Surface
Iron gives the characteristic Mars color: rusty red!
View of Viking 1
1 m rock
Sojourner
Martian Seasons:
Icecaps & Dust Storms
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!
Saturn’s Atmosphere
• 92% Hydrogen
7% Helium;
some methane,
water, ammonia
• Belt structure
similar to
Jupiter’s, but
fainter
• Storms are rarer
• White spot seen,
1990 (Voyager)
Uranus’ and Neptune’s Atmospheres
Neptune’s Dark Spot
• Ammonia frozen out; more methane
– Methane absorbs red light, leads to bluish color
• Almost no band structure on Uranus
• The most volcanically
active object in the
solar system
– Heated by tidal friction
• Eruptions as high as
200 miles, may last for
months
• No atmosphere
Jupiter’s moon Io
Saturn’s Moon Titan
• Titan is the only moon in the solar system
known to have an atmosphere
Infrared picture shows surface details
2005 Huygens Landing
• STRANGE TITAN: Get ready
for two of the strangest hours
in the history of space
exploration. That's how long it
will take the European Space
Agency's Huygens probe to
parachute to the surface of
Saturn's largest moon Titan
on January 14th. Huygens will
sample Titan's atmosphere,
photograph its bizarre terrain,
listen for alien sounds and,
possibly, splash down in a
liquid methane sea.
Landing Site on
Titan
• Rocks made from
methane ice
360° Panorama of Titan
Atmospheric Histories - Venus
• Venus is closer to Sun than Earth hotter
surface
• Not a lot of liquid water on surface initially
• CO2 could not be absorbed by water, rocks
because of higher temperatures
•  run-away Greenhouse effect: it’s hot, the
greenhouse gases can’t be be stored away, it
gets hotter …
Earth’s Atmospheric History
•
•
•
•
•
Volcanic activity spews out water steam
Temperature range allowed water to liquify
CO2 dissolves in oceans, damping greenhouse effect
More water condenses, more CO2 is absorbed
If too cold, ice forms  less cloud cover  more
energy
• No oxygen at this point, since it would have been
used up producing “rust”
• Tertiary atmosphere: early life contributes oxygen
– 1% 800 Myrs ago, 10% 400 Myrs ago
Mars – Freezing over
• Mars once had a denser atmosphere with liquid
water on the surface
• As on Earth, CO2 dissolves in liquid water
• But: Mars is further away from the Sun
 temperature drops below freezing point 
inverse greenhouse effect
• permafrost forms with CO2 locked away
• Mars probably lost its atmosphere because its
magnetic field collapsed, because Mars’ molten
core cooled down
Global Warming on Earth
• Excessively
“politicised” topic
• Very complex
problem
scientifically
• Slow changes over
long periods of time
• Could use more data
• Sources of heating,
sources of cooling
are temperature
dependent
Hard Facts: Measurements
• Undisputed: global temperatures go up
Man-made CO2 in the Atmosphere goes up
Correlation: Temperatures rise when
Carbon Dioxide levels rise
• This is true since prehistoric times
The Last Millennium – “Hockey Stick”
Is it for real?
• Virtually everyone agrees that average global
temperatures have risen by about 1 °F over the last
century
– May not sound like much, but during the last ice age
average temperatures were only about 8-9 F colder
than now
• Real question: is it due to human activity (the
greenhouse gases) or just natural variation?
• IPCC report
– “Most of the observed warming over the last 50 years is
likely to have been due to the increase in greenhouse
gas concentrations.”
A lot of human activities release
greenhouse gases
• No easy political solution  need concerted, global, long
term initiative
Possible Effects
• Rising sea levels and inundation of coastal areas
– But not: ocean front properties in Kansas in 20 years!
• More extreme weather (e.g. droughts followed by
periods of heavy rainfall and flooding, hurricanes,
monsoons, etc.)
• Disruption of agriculture
• Increases in malaria and other insect-borne
diseases
• …
Observing Inner
and Outer 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
Size of planet
varies a lot as
Earth moves
Earth
Outer planet
Far-Out Planet
Earth
Size of planet
varies little as
Earth moves
Outer planet
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!
• Saturn is visible later at night
Moon Phases
• Today (Waning Gibbous, 70%)
• 10 / 3 (Last Quarter Moon)
• 10/ 11 (New Moon)
• 10 / 19 (First Quarter Moon)
• 10 / 26 (Full Moon)
Today
at
Noon
Sun at
meridian,
i.e.
exactly
south
10 PM
Typical
observing
hour,
early
October
Moon
Uranus
Neptune
Star
Maps
Celestial
North Pole –
everything
turns around
this point
Zenith – the
point right
above you &
the middle of
the map
40º
90º
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
South 2006
• Planets
– Uranus
– Neptune
• Zodiac:
– Capricorn
– Aquarius
South –
2007
• Planets
– Uranus
– Neptune
• Zodiac:
– Capricorn
– Aquarius
Mark your Calendars!
• Next Starry Monday: November 5, 2006, 7 pm
(this is a Monday
• Observing at Prairie Oaks Metro Park:
– Friday, October 19, 7 pm
– Friday, November 16, 6:30 pm
– Friday, January 11, 6:00 pm
• Web pages:
– http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.)
– http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)
)
Mark your Calendars II
•
•
•
•
Physics Coffee is every Wednesday, 3:30 pm
Open to the public, everyone welcome!
Location: across the hall, Science 256
Free coffee, cookies, etc.