Astro 1 - Exam 3

Astro 1 - Exam 3 what is the sun comprised of? - ✔✔73% hydrogen 25% helium why is the sun stable? - ✔✔outward force of gas pressure; inward force of gravity Where does the gas pressure in the sun come from? - ✔✔nuclea ...

Astro 1 - Exam 3 what is the sun comprised of? - ✔✔73% hydrogen 25% helium why is the sun stable? - ✔✔outward force of gas pressure; inward force of gravity Where does the gas pressure in the sun come from? - ✔✔nuclear fusion reactions in the core at temperatures of 15 million degrees What is the diameter of the sun compared to earth? mass? luminosity (compared to 100W lightbulbs? - ✔✔diameter-109x; mass-333,000; luminosity- 4 x 10^24 What percent of mass in the solar system comes from the sun? - ✔✔99.9% how long has the sun been shining? how much longer will it shine? - ✔✔4.5 billion years; 5.5 billion years what are sunspots? - ✔✔slightly cooler regions on the sun's surface what causes sunspots? how long are their cycles? - ✔✔magnetic activity preventing hot material from rising to that region. they have 11 year cycles what comprises helium-4? What does it release? What is it called? - ✔✔4 protons combine to make helium-4 (2 protons, 2 neutrons); produces gamma rays; it is called the proton-proton chain What is the first step in Nuclear fusion? - ✔✔two protons stick together and one changes into a neutron to produce deuterium (1 proton and 1 neutron) What is the second step in Nuclear fusion? - ✔✔deuterium plus proton makes helium-3 (2 protons and 1 neutron bound together) What is the third step in nuclear fusion? - ✔✔two helium-3 molecules combine to make helium4 and 2 protons When is energy created in Nuclear fusion? - ✔✔in every step Where does the energy in Nuclear fusion come from? - ✔✔E= mc^2 because the mass of helium is 4 less than the mass of 4 protons What are the layers of the sun from inside to out? - ✔✔core, radiative zone, connective zone, photosphere, chromosphere, flare, prominence, corona, solar wind What is the core of the sun like? - ✔✔at center; high density and temperature; where nuclear reactions occur and gamma rays produced What is the radiative zone of the sun like? - ✔✔photons are repeatedly reabsorbed and emitted, and the energy of an individual photon can take on average 170,000 years to pass through What is the connective zone of the sun like? - ✔✔hot gas rises and cold gas sinks; light traverses in 1 week What is the photosphere of the sun like? - ✔✔temperature 5780K; the surface that we see; photons have been converted to visible wave- length, see granules due to convection bringing ma- terial up and down in cells What is the chromosphere of the sun like? - ✔✔red or orange color; temperature 4500K; we see through this to the photosphere What is the flare of the sun like? - ✔✔eruption coming out of Sun due to magnetic activity What is the prominence of the sun like? - ✔✔hoop shaped eruption out of Sun due to magnetic activity What is the corona of the sun like? - ✔✔low density; temperature 1 million K; visible during solar eclipse What is the solar wind of the sun like? - ✔✔charged particles coming from Sun's sur- face; permeate whole solar system What is luminosity? - ✔✔the absolute power output at the source What is brightness? - ✔✔apparent output as observed at some distance What determines how bright a star appears based upon its luminosity? - ✔✔inverse square law What is the inverse square law? - ✔✔B= L/4πd^2; b-brightness, d-distance, L- luminosity if two stars have the same luminosity and one is 10 times further away than the other, how bright will it appear? - ✔✔it will appear 1/10^2 as bright which is 100 times fainter What is the parallax method and what is it used for? - ✔✔used to measure distance; view stars from two locations on opposite sides of the sun (6 months apart). these locations are on opposite sides of the sun. What is the baseline of the parallax method? - ✔✔1 AU is the radius of the orbit of earth around the sun At what angle does the star appear to move relative to distant stars in the parallax method? - ✔✔the star appears to move (relative to distant stars) by an angle 2 times that of the parallax angle how do you determine distance in parsecs? - ✔✔D= 1/p; p- parsecs in arcseconds; Why is a star that appears fainter sometimes closer than a star that appears brighter? - ✔✔because the star the appears closer is more luminous lower mass stars: What was the suns history? - ✔✔stellar nursery, protostar, main sequence, red giant, planetary nebula, white dwarf lower mass stars: what are failed stars? - ✔✔brown dwarfs, have mass less than 8% of the sun and never heat enough to have nuclear reactions in their core lower mass stars: what is a planetary nebula? - ✔✔ejected envelope of a low to intermediate mass star lower mass stars: what is the end state? - ✔✔white dwarf; held up against gravity by pressure of electrons; size of earth more massive stars: short or longer life on main sequence? - ✔✔shorter more massive stars: What fuel is used? - ✔✔helium burning, then carbon burning, then onion shell burning, then swelling to red supergiant more massive stars: What does it stop burning at and why? - ✔✔stops burning at iron because iron is very stable and reactions involving iron do not produce energy more massive stars: How does it end? - ✔✔type II supernova with core left behind; supernova makes elements heavier than iron, including gold and silver more massive stars: what happens to the core? - ✔✔the core is 1.4-3 solar masses and becomes a neutron star=radius of 5-6 km, city sized more massive stars: what if the core is > 3 solar masses - ✔✔it becomes a black hole, infinitesimal radius; infinite destiny black holes: Where do they come from? - ✔✔it is the end state of a high mass star (> 40 solar masses), left behind after a supernova explosion black holes: can anything escape a black hole? can light? - ✔✔the gravity of collapsed (very dense) object is so large that even light cannot escape black holes: do black holes suck things in? - ✔✔black holes do not suck things in; if you are far enough away from them they act like normal objects withe the same mass black holes: what is the event horizon? - ✔✔the sphere around a black hole from within nothing can escape black holes: what can be used to measure the mass of a black hole? - ✔✔the speed of the orbit of a star in a binary star system with a black hole black holes: what would happen to a clock if if it was falling in a black hole? - ✔✔intense gravity of a black hole warps space so that a clock would appear to slow as it falls down black holes: what happens to object falling into a black hole? - ✔✔tidal forces are created near a black hole and objects are stretched because the force on the nearest part is so much larger than the force on the farthest part black holes: what is at the center? - ✔✔a singularity, a point of infinite destiny what happens at the end of its life with if a star begins with < 8 solar masses? - ✔✔the core becomes a white dwarf- collapse stop because of degeneracy pressure of electrons- radius same as earth what happens at the end of its life with if a star begins with 8-40 solar masses? - ✔✔the core becomes a neutron star- collapse stops because of degeneracy pressure of neutrons- radius of 5-6 km what happens at the end of its life with if a star begins with > 40 solar masses? - ✔✔the core becomes a black hole- collapse does not stop- mass concentrated at singularity When, where and by whom was the first extrasolar planet discovered? - ✔✔when-1992; wherein orbit around a dead neutron star; cannot support life; by whom- Penn State Prof. Alex Wolszczan What were many of the planets discovered in the late 1990's and early 2000's like? - ✔✔planets around the mass of Jupiter, that are very close to their stars How many planets has the Kepler mission discovered using the transit method? - ✔✔thousands; the brightness of the star decreases due to the planet passing right in front of it. How does the transit method find the distance of the planet to its star? What does this information help us discover? - ✔✔using Kepler's law . P^2 = a^3; it helps discover i the planet is in the hospitable zone and the amount of drop in the stars brightness helps us discover the size of the planet how many extrasolar planets have been discovered in the habitable zones around their stars? - ✔✔a dozen what is a habitable zone? - ✔✔region around a star where liquid water could be present on a planets surface Where would the habitable zone be on a less massive star? - ✔✔closer to the star Where would the habitable zone be on a more massive star? - ✔✔further away from the star Is life found in extreme conditions on Earth? - ✔✔yes, dark- ness, high radiation, acidic, underground, in methane ice, extreme heat What is drakes equation? what is it used for? - ✔✔N =R∗×fp ×ne ×fl ×fi ×fc ×L (p,e,l,i,c are subscripts); method used to estimate the number (N) of communicating/ technological civilizations in our galaxy What is R* in Drake's equation? - ✔✔rate of star formation, number of stars forming per year in our galaxy, around one solar mass per year What is f(subscript) p in Drake's equation? - ✔✔percentage of stars that form planets What is n (subscript)e Drake's equation? - ✔✔average number of planets that could support life for each star What is f(subscript)l Drake's equation? - ✔✔percentage of those planets where life occurs What is f (subscript) i Drake's equation? - ✔✔percentage of those planets where intelligence develops What is F(subscript)c Drake's equation? - ✔✔percentage of intelligent species that communicates What is L Drake's equation? - ✔✔average lifetime of a communicating species What are the properties of a star? - ✔✔luminosity, mass, size, temperature, and age What affects the luminosity of a star? - ✔✔size and temperature directly affect luminosity; larger size = larger light-emitting area = greater luminosity; higher temperature = greater luminosity Where are main sequence stars located on the H-R diagram? - ✔✔they form a band from the lower right across the upper left What are stars on the main sequence burning as fuel? - ✔✔hydrogen into helium for stars on the main sequence does higher temperature= higher luminosity? - ✔✔yes Where do red dwarfs (cool, faint, and small) fall on the H-R diagram? blue giants (hot, bright, and large)? (main sequence) - ✔✔red dwarfs (cool, faint, and small) on lower right; blue giants (hot, bright and large) on upper left What determines where on the main sequence a star lives, and what the main sequence lifetime is for the star? - ✔✔mass; more-massive main sequence stars are on the upper left of H-R diagram; masses range from about 0.1 to 100 times the mass of the Sun; sizes range from 0.1 to 15 times the radius of the Sun Where does luminosity range from on the main sequence stars (compared to the sun)? - ✔✔luminosities of main sequence stars range from 10^−3 to 10^6 times that of the Sun for main sequence stars, how does the age range from those stars? - ✔✔age ranges from few million years for more massive stars to much more than 14 billion years (age of the universe) for less massive stars; REMEMBER, the more massive stars use their greater fuel supply more rapidly What are red giants and supergiants NOT on the main sequence like? - ✔✔burning helium not hydrogen anymore; starting to die; size is large, so they are luminous even though they are relatively cool What are white dwarfs NOT on the main sequence like? - ✔✔hot, small and dim, so fall on lower left of H-R diagram; dying stars Can you identify on the H-R diagram - ✔✔hot and cold stars; blue and red stars high and low luminosity stars large radius and small radius stars high mass and low mass stars stars converting hydrogen to helium at their cores red giants and white dwarfs stars that will have a long or short lifetime What is the H-R diagram? - ✔✔Hersprung-Russell diagram What color are cooler stars? hotter stars? - ✔✔cooler stars- redder; hotter stars- bluer on the H-R diagram what axis is surface temperature on? - ✔✔horizontal axis, increasing to the left How is temperature measured on the H-R diagram? - ✔✔using the spectral class how do spectral classes of stars run from hotter to cooler on the H-R diagram? what is the acronym for this? - ✔✔OBAFGKM; oh, be a fine guy/girl, kiss me how is spectral class determined on the H-R diagram? - ✔✔using the absorption spectrum, where absorption lines from different chemical elements with different levels of ionization arise at different temperatures What axis is luminosity expressed on in the H-R diagram? - ✔✔vertical axis, increasing to top; ex- pressed in terms of the luminosity of the Sun, a solar luminosity What is the closest star and how far away is it? - ✔✔Alpha centauri, 4.3 million light years away or 1.35 parsecs, from the sun Is the nearest star to the sun a singular star system? - ✔✔no it is a triple star system; the brightest member similar to the sun What are most of the nearest stars like and where do they fall on the H-R diagram? - ✔✔Most of the nearest stars are cool and dim and fall on the lower right of the H-R diagram; this is because most stars have these properties. What is the brightest star in the nighttime sky? how massive is it compared to the sun? is it a singular star system? - ✔✔sirius is twice as massive as the sun. its companion is a white dwarf how do the brightest stars fall on the H-R diagram? where do they fall? - ✔✔brightest stars have more varied properties, red and blue, low and high luminosity, with some on the lower right of the H-R diagram, but others near where the Sun is, some on the upper left, and some on the upper right (red giant region) are the brightest stars always the closest? - ✔✔brightest stars tend to be biased towards stars that have large luminosities, so that they appear bright to us even at large distances; we simply can't see low- luminosity stars if they are too far away What is luminosity? - ✔✔the absolute power output at the source What is brightness? - ✔✔apparent output as observed at some distance What determines how bright a star appears based upon its luminosity? - ✔✔inverse square law What is the inverse square law? - ✔✔B= L/4πd^2; b-brightness, d-distance, L- luminosity if two stars have the same luminosity and one is 10 times further away than the other, how bright will it appear? - ✔✔it will appear 1/10^2 as bright which is 100 times fainter What is the parallax method and what is it used for? - ✔✔used to measure distance; view stars from two locations on opposite sides of the sun (6 months apart). these locations are on opposite sides of the sun. What is the baseline of the parallax method? - ✔✔1 AU is the radius of the orbit of earth around the sun At what angle does the star appear to move relative to distant stars in the parallax method? - ✔✔the star appears to move (relative to distant stars) by an angle 2 times that of the parallax angle how do you determine distance in parsecs? - ✔✔D= 1/p; p- parsecs in arcseconds; Why is a star that appears fainter sometimes closer than a star that appears brighter? - ✔✔because the star the appears closer is more luminous