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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 • • • • • • 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 • • • • • • 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 • • • • • • 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 • • • • • • 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 • • • • • • 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 • • • • • • 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 • • • • • • 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 • • • • • 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 • • • • 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 • • • • 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 • • • • 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