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Astronomy 101 The Solar System Tuesday, Thursday 2:30-3:45 pm Hasbrouck 20 Tom Burbine [email protected] Course • Course Website: – http://blogs.umass.edu/astron101-tburbine/ • Textbook: – Pathways to Astronomy (2nd Edition) by Stephen Schneider and Thomas Arny. • You also will need a calculator. Office Hours • Mine • Tuesday, Thursday - 1:15-2:15pm • Lederle Graduate Research Tower C 632 • Neil • Tuesday, Thursday - 11 am-noon • Lederle Graduate Research Tower B 619-O Homework • We will use Spark • https://spark.oit.umass.edu/webct/logonDisplay.d owebct • Homework will be due approximately twice a week Astronomy Information • Astronomy Help Desk • Mon-Thurs 7-9pm • Hasbrouck 205 • The Observatory should be open on clear Thursdays • Students should check the observatory website at: http://www.astro.umass.edu/~orchardhill for updated information • There's a map to the observatory on the website. Final • Monday - 12/14 • 4:00 pm • Hasbrouck 20 HW #10 • Due today HW #11 • Next Tuesday If you want to find life outside our solar system • You need to find planets • http://exoplanet.eu Extrasolar Planets • Today, there are over 400 known extrasolar planets Star Names • A few hundred have names from ancient times • Betelgeuse, Algol, etc. • Another system: • A star gets name depending on what constellation it is in • With a Greek letter at the beginning – Alpha Andromeda, Beta Andromeda, etc. • Only works for 24 brightest star Star Names now • Stars are usually named after the catalog they were first listed in • HD209458 is listed in the Henry Draper (HD) Catalog and is number 209458 • HD209458a is the star • HD209458b is the first objects discovered orbiting the star Our Solar System has basically two types of planets • Small terrestrial planets – Made of Oxygen, Silicon, etc. • Large gaseous giants – Made primarily of hydrogen and a little helium – – – – Jupiter - 90% Hydrogen, 10% Helium Saturn – 96% Hydrogen, 3% Helium Uranus – 83% Hydrogen, 15% Helium Neptune – 80% Hydrogen, 20% Helium Things to Remember • The Milky Way has at least 200 billion other stars and maybe as many as 400 billion stars • Jupiter’s mass is 318 times than the mass of the Earth Question: • How many of these stars have planets? What is the problem when looking for planets? What is the problem when looking for planets? • The stars they orbit are much, much brighter than the planets • Infrared image of the star GQ Lupi (A) orbited by a planet (b) at a distance of approximately 20 times the distance between Jupiter and our Sun. • GQ Lupi is 400 light years from our Solar System and the star itself has approximately 70% of our Sun's mass. • Planet is estimated to be between 1 and 42 times the mass of Jupiter. • http://en.wikipedia.org/wiki/Image:GQ_Lupi.jpg So what characteristics of the planets may allow you to “see” the planet So what characteristics of the planets may allow you to “see” the planet • Planets have mass • Planets have a diameter • Planets orbit the star http://upload.wikimedia.org/wikipedia/commons/d/de/Extrasolar_Planets_2004-08-31.png • Jupiter – – – – H, He 5.2 AU from Sun Cloud top temperatures of ~130 K Density of 1.33 g/cm3 • Hot Jupiters – – – – – – H, He As close as 0.03 AU to a star Cloud top temperatures of ~1,300 K Radius up to 1.3 Jupiter radii Mass from 0.2 to 2 Jupiter masses Average density as low as 0.3 g/cm3 10 100 1,000 (lightyears) Some Possible Ways to detect Planets • • • • Pulsar Timing Radial Velocity (Doppler Method) Transit Method Direct Observation Pulsars • Rotating Neutron Stars • Have densities of 8×1013 to 2×1015 g/cm³ • http://www-learning.berkeley.edu/astrobiology/powerpointhtml/sld035.htm • http://en.wikipedia.org/wiki/Image:Ssc2006-10c.jpg Would you want to live on a pulsar planet? Center of Mass • Distance from center of first body = distance between the bodies*[m2/(m1+m2)] • http://en.wikipedia.org/wiki/Doppler_spectroscopy Radial Velocity (Doppler Method) http://www.psi.edu/~esquerdo/asp/shifts.jpg • http://astronautica.com/detect.htm Wavelength http://www.psi.edu/~esquerdo/asp/method.html www.physics.brandeis.edu/powerpoint/Charbonneau.ppt Bias • Why will the Doppler method will preferentially discover large planets close to the Star? Bias • Why will the Doppler method will preferentially discover large planets close to the Star? • The gravitational force will be higher • Larger Doppler Shift Transit Method • When one celestial body appears to move across the face of another celestial body • When the planet crosses the star's disk, the visual brightness of the star drops a small amount • The amount the star dims depends on its size and the size of the planet. • For example, in the case of HD 209458, the star dims 1.7%. • http://en.wikipedia.org/wiki/Extrasolar_planets#Transit_method One major problem • Orbit has to be edge on Eclipse • Planet passes in back of a star • http://www.news.cornell.edu/stories/March05/Planet-eclipse-Plot.mov • Because the star is so much brighter than a planet, the dip in brightness is smaller during an eclipse than a transit • Usually to maximize the effects of an eclipse, astronomers observe these eclipses at infrared wavelengths Direct Observation • Infrared Image Visible • • Infrared http://www.news.cornell.edu/stories/March05/extrasolar.ws.html http://nai.nasa.gov/library/images/news_articles/319_1.jpg http://en.wikipedia.org/wiki/Image:Extrasolar_planet_NASA2.jpg How did these Hot Jupiters get orbits so close to their stars? How did these Hot Jupiters get orbits so close to their stars? • Formed there – but most scientists feel that Jovian planets formed far from farther out • Migrated there - planet interacts with a disk of gas or planetesimals, gravitational forces cause the planet to spiral inward • Flung there – gravitational interactions between large planets Kepler Mission • Kepler Mission is a NASA space telescope designed to discover Earth-like planets orbiting other stars. • Using a space photometer, it will observe the brightness of over 100,000 stars over 3.5 years to detect periodic transits of a star by its planets (the transit method of detecting planets) as it orbits our Sun. • Launched March 6, 2009 Kepler Mission http://en.wikipedia.org/wiki/File:Keplerpacecraft.019e.jpg Kepler Mission • The Kepler Mission has a much higher probability of detecting Earth-like planets than the Hubble Space Telescope, since it has a much larger field of view (approximately 10 degrees square), and will be dedicated for detecting planetary transits. • There will a slight reduction in the star's apparent magnitude, on the order of 0.01% for an Earthsized planet. www.physics.brandeis.edu/powerpoint/Charbonneau.ppt KEY D 22255311322343524233524343125151 35254313 What Planet do we know the most about? • Earth http://college.cengage.com/geology/resources/protected/physicallab/thelab/interior/index.htm Earth’s Interior Earth’s crust • • • • • • • • 46.6% O 27.7% Si 8.1% Al 5.0% Fe 3.6% Ca 2.8% Na 2.6% K 2.1% Mg Earth is made of minerals Mineral • A naturally occurring, homogeneous inorganic solid substance having a definite chemical composition and characteristic crystal structure Olivine • (Mg, Fe)2SiO4 • Fayalite (Fa) - Fe2SiO4 • Forsterite (Fo) - Mg2SiO4 Pyroxenes • XY(Si, Al)2O6 • X can be Ca, Na, Fe+2, Mg, Zn, Mn, and Li • Y can be Cr, Al, Fe+3, Mg, Mn, Sc, Ti, V, and Fe+2 Augite Ferrosilite How do we know what’s in the interior of the Earth? How do we know what’s in the interior of the Earth? • Seismic Waves – vibrations created by earthquakes Seismic Waves • P waves – primary waves – (pushing) – travel faster – can travel through anything • S waves – secondary – (side to side) – travel slower – only through solids • http://alomax.free.fr/alss/examples/hodo/hodo_ex ample.html Surface Waves • Travel on the surface of the Earth • Love Wave – side by side • http://www.geo.mtu.edu/UPSeis/images/Love_ani mation.gif • Rayleigh Wave – rolling movement • http://www.geo.mtu.edu/UPSeis/images/Rayleigh _animation.gif • Most of the shaking felt from an earthquake is due to the Rayleigh waves P (primary) waves S (secondary) waves Surface waves: Rayleigh and Love waves Richter Scale • Measures the magnitude of an earthquake • Single number to quantify the amount of seismic energy released by an earthquake. Amplitude of largest displacement • Under 6.0 - At most slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings. • 6.1-6.9 - Can be destructive in areas up to about 100 kilometers across where people live. • 7.0-7.9 - Major earthquake. Can cause serious damage over larger areas. • 8 or greater - Great earthquake. Can cause serious damage in areas several hundred kilometers across. How do we get information? • The precise speed and direction of the waves depends on the composition, density, pressure, temperature, and phase (solid or liquid) Which of these bodies have they used seismic waves to study? • Earth • Moon – Apollo missions brought seismometers to Moon to study moonquakes How can you study the interior of a planet from space? Density • Density = mass/volume • If the density is higher than the surface rock, there must be denser material in the interior Gravity • If you can measure gravity (force) with a spacecraft as it rotates around a body, you can determine how mass is distributed on the body Magnetic Field • Tells if a planet has a molten metal interior http://www.gcsescience.com/pme1.htm Earth’s magnetic field is believed to be caused by the convection of molten iron, within the outer liquid core along with the rotation of the planet Electrons flow http://geomag.usgs.gov/images/faq/Q6.jpg http://www.scifun.ed.ac.uk/card/images/left/earth-magfield.jpg • Magnetic pole moves http://science.nasa.gov/headlines/y2003/29dec_magneticfield.htm http://science.nasa.gov/headlines/y2003/29dec_magneticfield.htm North Magnetic Pole • However, the "north pole" of a magnet is defined as the one attracted to the Earth's North Magnetic Pole • By this definition, the Earth's North Magnetic Pole is physically a magnetic south pole Glatzmeier and Roberts simulations: Geomagnetic Reversals • Based upon the study of lava flows of basalt throughout the world, it has been proposed that the Earth's magnetic field reverses at intervals, ranging from tens of thousands to many millions of years • The average interval is ~250,000 years. • The last such event, called the BrunhesMatuyama reversal is theorized to have occurred some 780,000 years ago. • The present strong deterioration corresponds to a 10– 15% decline over the last 150 years and has accelerated in the past several years • Geomagnetic intensity has declined almost continuously from a maximum 35% above the modern value, which was achieved approximately 2000 years ago. • At this rate, the dipole field will temporarily collapse by 3000–4000 AD What may happen during the reversal? • There may be a slight rise in the per capita cancer rate due to a weaker magnetic field. • We may also be able to see the northern lights at lower latitudes • If you own a compass, it will have difficulty finding north until the magnetosphere settles. Van Allen Belts • The Van Allen radiation belts are rings of energetic charged particles around Earth, held in place by Earth's magnetic field • Outer belt – primarily electrons • Inner belt – primarily protons http://www.nytimes.com/2006/08/10/science/space/10vanallen.html Van Allen Belts http://en.wikipedia.org/wiki/Image:Van_Allen_radiation_belt.svg http://csep10.phys.utk.edu/astr161/lect/earth/magnetic.html James Van Allen • Sent a Geiger Counter on the first US satellite Explorer 1 • The Geiger counter began clicking madly as soon as it reached orbit Auroras • Auroras – natural light displays • Collision of charged particles from Earth's magnetosphere with atoms and molecules of Earth's upper atmosphere • The collisions in the atmosphere electronically excite atoms and molecules in the upper atmosphere. The excitation energy can be lost by light emission or collisions. • http://www.youtube.com/watch?v=pLi4T4JCALk Any Questions?