Transcript Monday, March 31 - Otterbein University

Planetary Atmospheres &
Introduction to Stars
IS Symposium
• Just a reminder that all IS students are encouraged to attend and
participate in next week's campus conversation "Complicating
Normal--A Campus Conversation on Dis/Ability." Several
programs are featured including:
• LeDerick Horne, April 1, 1:15 p.m. in Riley Auditorium. A gifted
word poet, playwright and disability advocate, LeDerick's talk is
titled "Beyond Classification." An informal reception follows the
presentation.
• Panel on Disability Experience, April 1, 7 p.m. in Towers 110
• Lennard Davis, April 2, 3:30 p.m. in Roush 114. Dr. Davis is a
professor of English, professor of disability and human development and
professor of medical education at the University of Illinois at Chicago. He
directs Project Biocultures, a think tank devoted to issues found at the
intersection of disability, culture, medicine, biotechnology and biosphere. His
talk is "The End of Normal: Disability, Diversity and Neoliberalism."
Mercury
• Small, bright but hard
to see
• About the same size as
the moon
• Density about that of
Earth
• Day ~ 59 Earth days
• Year ~ 88 Earth days
Venus
• Bright, never very far
from the sun
– “Morning/Evening star”
• Similar to Earth in size
and density
• Day ~ 243 Earth days
(retrograde!)
• Year ~ 225 Earth days
Venus
• Very thick atmosphere,
mostly CO2
• Heavy cloud cover (sulfuric
acid!)
– About 90 times the pressure
of Earth’s atmosphere
– Very strong greenhouse
effect, surface temperature
about 750 K
• No magnetic field
Surface
Features
• Two large
“continents”
– Aphrodite Terra and
Ishtar Terra
– About 8% of the
surface
• Highest peaks on
Aphrodite Terra rise
about 14 km above
the deepest surface
depression
– Comparable to
Earth’s mountains
Hothouse Venus: 850 °F
• Fairly bright, generally
not too hard to see
• Smaller than Earth
• Density similar to that
of the moon
• Surface temperature
150–250 K
• Day ~ 24.6 hours
• Year ~ 2 Earth years
• Thin atmosphere,
mostly carbon dioxide
– 1/150 the pressure of
Earth’s atmosphere
• Tiny magnetic field, no
magnetosphere
Mars
Mars
• Northern Hemisphere
basically huge volcanic
plains
– Similar to lunar maria
• Valles Marineris –
Martian “Grand Canyon”
– 4000 km long, up to 120
km across and 7 km deep
– So large that it can be seen
from Earth
Martian Volcanoes
• Olympus Mons
– Largest known volcano in the solar system
– 700 km across at base
– Peak ~25 km high (almost 3 times as tall as Mt. Everest!)
Martian Seasons:
Icecaps & Dust Storms
Martian Surface
Iron gives the characteristic Mars color: rusty red!
View of Viking 1
1 m rock
Sojourner
Water on Mars?
Mars
Louisiana
Runoff channels
Outflow Channels
Life on Mars?
• Giovanni Schiaparelli (1877) – observed “canali”
(channels) on Martian surface
• Interpreted by Percival Lowell (and others) as
irrigation canals – a sign of intelligent life
• Lowell built a large observatory near Flagstaff, AZ
(Incidentally, this enabled C. Tombaugh to find Pluto in 1930)
• Speculation became more and more fanciful
– A desert world with a planet-wide irrigation system to carry
water from the polar ice caps?
– Lots of sci-fi, including H.G. Wells, Bradbury, …
• All an illusion! There are no canals…
Viking Lander Experiments
(1976)
• Search for bacterialike forms of life
• Results inconclusive
at best
Atmospheric Histories
• Primary atmosphere: hydrogen, helium,
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
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
Stellar Parallax
• Given p in arcseconds (”), use
d=1/p to calculate the distance
which will be in units “parsecs”
• By definition, d=1pc if p=1”, so
convert d to A.U. by using
trigonometry
• To calculate p for star with d given
in lightyears, use d=1/p but
convert ly to pc.
• Remember: 1 degree = 3600”
• Note: p is half the angle the star
moves in half a year
Our Stellar Neighborhood
Scale Model
• If the Sun = a golf ball, then
–
–
–
–
–
Earth = a grain of sand
The Earth orbits the Sun at a distance of one meter
Proxima Centauri lies 270 kilometers (170 miles) away
Barnard’s Star lies 370 kilometers (230 miles) away
Less than 100 stars lie within 1000 kilometers (600 miles)
• The Universe is almost empty!
• Hipparcos satellite measured distances to nearly 1
million stars in the range of 330 ly
• almost all of the stars in our Galaxy are more distant
Luminosity and Brightness
• Luminosity L is the total power
(energy per unit time) radiated
by the star, actual brightness of
star, cf. 100 W lightbulb
• Apparent brightness B is how
bright it appears from Earth
– Determined by the amount of
light per unit area reaching Earth
– B  L / d2
• Just by looking, we cannot tell
if a star is close and dim or far
away and bright
Brightness: simplified
• 100 W light bulb will look
9 times dimmer from 3m
away than from 1m away.
• A 25W light bulb will look
four times dimmer than a
100W light bulb if at the
same distance!
• If they appear equally
bright, we can conclude that
the 100W lightbulb is twice
as far away!
Same with stars…
• Sirius (white) will look 9
times dimmer from 3
lightyears away than from 1
lightyear away.
• Vega (also white) is as
bright as Sirius, but appears
to be 9 times dimmer.
• Vega must be three times
farther away
• (Sirius 9 ly, Vega 27 ly)
Distance Determination Method
• Understand how bright an object is
(L)
• Observe how bright an object appears (B)
• Calculate how far the object is away:
B  L / d2
So
L/B  d2 or
d  √L/B
Homework: Luminosity and Distance
• Distance and brightness can be used to find
the luminosity:
L  d2 B
• So luminosity and brightness can be used to
find Distance of two stars 1 and 2:
d21 / d22 = L1 / L2 (since B1 = B2 )
i.e. d1 = (L1 / L2)1/2 d2
Homework: Example Question
• Two stars -- A and B, of
luminosities 0.5 and 2.5 times the
luminosity of the Sun, respectively -- are
observed to have the same apparent
brightness. Which one is more distant?
• Star A
• Star B
• Same distance
Homework: Example Question
• Two stars -- A and B, of luminosities 0.5 and 2.5 times the
luminosity of the Sun, respectively -- are observed to have the
same apparent brightness.
How much farther away is it than the other?
• LA/d2A = BA =BB = LB/d2B  dB = √LB/LA dA
•  Star B is √5=2.24 times as far as star A