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Context
• The audience for this activity was two
sections of Regents Earth Science
primarily composed of 9th grade students.
• The students were heterogeneously
grouped with an aid in the classes on hand
to assist students with special needs.
• Prior to the competition of the activity the
students took notes on the material in a
lecture format.
Characteristics of Stars
Characteristics of Stars
• Apparent magnitude is how bright stars
look to us in the sky from here on Earth
• A dim star that is nearby looks bright,
while a very bright star that is far away
looks dim
Characteristics of Stars
• Absolute Magnitude- astronomers
"pretend" to line up stars exactly 10
parsecs (about 32.6 light years) away
from Earth.
• They then figure out how bright each
star would look.
Characteristics of Stars
• luminosity is the amount of energy a
body radiates per unit time
Spectral Classes
• Stars can be classified by their surface
temperatures
• Each class is represented by a letter, O,B,A,F,G,K,M
• These classes go from hot to cool with O the hottest
and M, coolest.
Spectral Class O
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Temperature-=28,000 - 50,000 K
Color - Blue
Mass compared to the Sun-=20 - 60
Radius compared to the Sun= 9-15
Luminosity compared to the Sun =90,000 - 800,000
Life as a main sequence star=1 - 10 Myr
Spectral Class B
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Temperature= 10,000-28,000 K
Color = Blue-White
Mass compared to the Sun= 3-18
Radius compared to the Sun= 3.0-8.4
Luminosity compared to the Sun =95-52,000
Life as a main sequence star-=11- 400 Myr
Spectral Class A
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Temperature= 7,500- 10,000K
Color = White
Mass compared to the Sun= 2.0-3.0
Radius compared to the Sun= 1.7-2.7
Luminosity compared to the Sun= 8-55
Life as a main sequence star= 400 Myr - 3 Gyr
Spectral Class F
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Temperature= 6,000- 7,500 K
Color = White-Yellow
Mass compared to the Sun= 1.1-1.6
Radius compared to the Sun= 1.2-1.6
Luminosity compared to the Sun = 2.0-6.5
Life as a main sequence star= 3.0-7.0 Gyr
Spectral Class G
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Temperature= 4,900-6,000K
Color = Yellow
Mass compared to the Sun= 0.85- 1.1
Radius compared to the Sun= 0.85- 1.1
Luminosity compared to the Sun =0.66-1.5
Life as a main sequence star= 7.0-15.0 Gyr
Spectral Class K
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Temperature= 3,500-4,900
Color = Orange
Mass compared to the Sun= 0.65-0.85
Radius compared to the Sun= 0.65-0.85
Luminosity compared to the Sun = 0.10-0.42
Life as a main sequence star=17Gyr
Spectral Class M
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Temperature= 2,000-3,500
Color = Red
Mass compared to the Sun= 0.08-0.05
Radius compared to the Sun=0.17-0.63
Luminosity compared to the Sun = 0.0010-0.008
Life as a main sequence star= 56 Gyr
Habitable Zones
• In 2009 NASA launched the Kepler Space
Observatory which was specifically designed to
survey a portion of our region of the Milky Way
galaxy to discover Earth-size planets in or near
the Habitable Zone.
• The term Habitable Zone describes an
imaginary spherical shell surrounding a star
throughout which the surface temperatures of
any planets present might be conducive to the
development of life as we know it
Image from European Southern
Observatory
Habitable Zones
• Scientists have defined the Habitable
Zone around a star as the region where
liquid water may be present.
• Under the standard pressure of our
atmosphere, water exists as a liquid
between 273K and 373K.
Factors Influencing the Habitable Zone
• The structure and composition of a
planets atmosphere
• the size of the planet,
• tectonic forces acting on the planet,
• the mineralogy of the rocks on the
planets surface,
• The Luminosity of the Star the planet
orbits.
Luminosity and Habitable Zones
• Luminosity- the amount of energy radiated
from a star
– Determined by Radius and Temperature
• Flux (S)-is the amount of energy passing
through an area perpendicular to the
radiation beam per unit time.
– Flux is a measurement of how much energy
strikes the surface of a planet/meter
squared/second
Luminosity and Habitable Zones
• Flux from a star drops off such that
the intensity is inversely proportional to
the distance from the source.
• The farther you are from a star the
weaker the flux
Luminosity and Habitable Zones
• The Habitable Zone for our solar
system, based on the factors described
earlier, has been estimated to be
between 0.8 AU and 1.5 AU.
• AU- Astronomical Unit is equal to the
distance between the Earth and the
Sun.
– 149,597,870 km (about 93 million miles)
Calculating Habitable Zones
• L (star)/L (sun) = r (star) 2/r (sun) 2
– L (sun) = the luminosity of the sun
– L (star) = Luminosity of the star relative to
the sun
– r (star) = The radius of the habitable zone
around the star
– r (sun) = The radius of the habitable zone
around the sun
Calculating Habitable Zones
• Example Calculation• Sirius A is a blue-white main sequence
stars with luminosity approximately 23
times that of the sun. To determine the
inner and outer boundaries around this
star in AU, we would use the following
calculations.
Calculating Habitable Zones
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L (star)/L (sun) = r (star) 2/r (sun) 2
Inner boundary = (23)/1 = (r2)/(0.8)2
(23)*(0.64) = r2
r2 = 14.7
Radius of inner boundary = 3.8 AU
Calculating Habitable Zones
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Outer boundary = (23)/1 = (r2)/(1.5)2
(23)*(2.25) = r2
r2 = 51.75
Radius of outer boundary = 7.2 AU
Calculating Habitable Zones
• The width of the habitable zone for this
star is equal to the outer boundary-the
inner boundary.
• 7.2 AU-3.8 AU= 3.4 AU
– Scientists believe that for life to exist on a
planet orbiting this star it would have to be in
this region.
• How does this compare to our Sun’s
Habitable Zone?
• Why the difference?
Stars and the development of life on planets
• The habitable zone around small stars tends to be very close to
the star.
• If the distance between a planet and the star it is orbiting is
small the gravitational force between the two objects can cause
the orbiting planet’s period of rotation to become equal to its
period of revolution.
• This is referred to as tidal locking. The result is that only one
side of the planet faces the star and is always illuminated, the
other side never faces the star and is always dark.
– The Earth’s moon is an example of this phenomenon.
Under Construction
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Why Earth and Not Mars?
In this activity students
investigate some of the physical
characteristics of Earth and
Mars along with some of the
geological and meteorological
processes that control that
influence the development of
life on each planet.
The students are asked to
research information plate
tectonics, climate, and weather
conditions on Earth and Mars
Students develop an
understanding of the
interconnected nature of those
processes and how they
collectively impact the
habitability of a planet.
Under Construction
• A Case for Life on Mars
• In this activity students
research different groups of
terrestrial extremophiles.
• This will help students to
better understand how the
boundaries of the range of
tolerance for life have been
expanded and how that has
provided new hope that life
can be found on Mars.
Under Construction
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Detecting Life in “Martian
Water”
Students are asked to design a
controlled experiment to
detect the presence of life in
the sample of Martian water.
The organism that will be used
in the experiment by the
students is Bacillus subtilis.
Bacillus subtilis would be a
reasonable analog to represent
a Martian organism because of
its ability to produces a unique
type of resting cell called an
endospore during unfavorable
conditions such as
temperature extremes, high
UV irradiation, and desiccation.
http://www.micro.cornell.edu/cals/micro/research/labs/angertlab/endo3.cfm
Under Construction
• The Martian water
activity is designed to use
Mars as a context to help
students improve their
understanding of the
functional definition of
life as well as designing
and performing controlled
scientific experiments.
• Students will use high
tech data collection
instruments to provide
them with a more
authentic research
experience.
Looking for Input
• Detecting Extrasolar Planets
– http://kepler.nasa.gov/multimedia/Interactives/ke
plerFlashAdvDiscovery/
Looking for Input
• Calculating the temperature of a planet
(no atmosphere)
• The importance of an atmosphere.
– Directly measuring the current content of
the earth’s atmosphere
– Using rocks to determine the composition
of the earths early atmosphere
– Measuring the composition of the
atmosphere's of other planets
Looking for Input
• What properties of water make it
necessary for life?
– Students perform experiments to measure
the properties of water and relate those
properties to their biological significance.
– http://nanosense.org/activities/finefilters
/scienceofwater/FF_Lesson2Student.pdf
References
• http://www.micro.cornell.edu/cals/micro/resea
rch/labs/angert-lab/endo3.cfm
• http://www.dirtyskies.com/index.php/2006/03
/08/terragen-mars-planum-boreum/
• http://nssdc.gsfc.nasa.gov/nmc/masterCatalog.
do?sc=1975-075C&ex=03
• http://www.callnrg.com/BacillusSubtilsBrochur
e.pdf
• http://www.daviddarling.info/encyclopedia/H/h
abzone.html
• How to Find a Habitable Planet by James
Kastings