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Astronomy Final Exam Review

by: Anna Cappelli

Astronomy Final Exam Review AST1002

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Anna Cappelli
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this is the final exam review for AST1002
Discovering the Universe
Reyes,Francisco J.
Study Guide
50 ?




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This 22 page Study Guide was uploaded by Anna Cappelli on Saturday April 23, 2016. The Study Guide belongs to AST1002 at University of Florida taught by Reyes,Francisco J. in Fall 2015. Since its upload, it has received 24 views. For similar materials see Discovering the Universe in Astronomy at University of Florida.


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Date Created: 04/23/16
Wednesday, April 20, 2016 Final Review Chapter 0 – Charting the Heavens If a star has a Declination of -30 degrees, in which celestial hemisphere is it located and how far the celestial equator? it would be in the souther hemisphere, 30 degrees away from the equator What are the names of the two points in the celestial sphere where the Sun crosses the celestial equator? vernal equinox and autumnal equinos Declination of the Sun for Summer solstice? For Winter solstice? the ecliptic has a 23.5 degree angel from the celestial equator, winter solstice in in south hemisphere and summer solstice is in the north hemisphere What is the relative location of the Moon, Sun and Earth for the different phases of the Moon? Where is the Sun respect to the Moon when it is full Moon. Where is the Sun when it is new Moon? when the moon is full the sun and moon are on opposite sides of the earth, when the moon is new they are on the same side Where is the Moon respect to the Sun’s position for a lunar eclipse? For a solar eclipse? lunar eclipse- full moon, moon and sun on opposite sides of earth 1 Wednesday, April 20, 2016 solar eclipse - new moon, same side Why we don’t see a solar or lunar eclipse every month? Why there are annular solar eclipses? the moon’s orbit around earth is an ellipse so one side (perigee) is closer to the earth than the other (apogee) The 5 degrees difference is the orientation of the Earth orbital plane and the Moon orbital plane eclipses only occur when the moon crosses the ecliptic while it is a new/full moon What causes the seasons? Is it the changing distance of the Earth to the Sun? Do we have winter or summer in the north and southern hemisphere at the same time? Is it the tilt of the Earth rotational axis? the earth’s rotation axis is tilted 23.5 degrees from the perpendicular plane of the ecliptic — earth is close to the sun during the north hemisphere winter an farther during north hemisphere summer (earth has an elliptical orbit) What is the Earth’s precession? What causes the Earth’s precession? gravitational pull of the sun and the moon on the earth causes it’s spin axis to precess like a spinning top What is the effect of the precession in the position of the star Polaris? result: celestial poles point in different directions in the sky as the earth precesses so Polaris is NOW close to north celestial pole but in 9,000 years, it will be close to star Vega What is the duration of the precession cycle? 26,000 years What is parallax and stellar parallax? apparent displacement of objects in the sky How can we use stellar parallax to calculate distance to a nearby star? yes, if we measure the angle of displacement of the object and we know the length of the baseline (earth diameter) we can calculate the distance to the object the amount of parallax is inversely proportional to object’s distance 2 Wednesday, April 20, 2016 Chapter 1 – The Copernican revolution How was retrograde motion explained in the geocentric model? “optical illusion” How do we explain the retrograde motion of Mars under the heliocentric model? occasional westward movement causing the planet to appear to make loops What was Tyco Brahe contribution to astronomy? he recorded superb naked eye positions of planets and built large instrument that allowed him to observe planets but they didn’t have optics Which are the 3 Kepler ‘s laws of planetary motion? 1st Law: Planets orbit the Sun in elliptical orbits 2nd Law: The line connecting a planet with the Sun sweep equal areas in equal times 3rd Law: p2 = a3. Modified 3rd law by Newton: p2 = a3/M Which are the 3 Newton’s law a motion? 1- an object at rest remains at rest, and a moving object continues to move forever in a straight line with constant speed, unless some external force changes their state of motion 2-the acceleration of an object is directly proportional to the net applied force and inversely proportional to the object’s mass 3- every action has its equal opposite reaction Newton law a gravity. How the gravitational force between two masses changes if we change one of the masses? How does it change if we change the distance? newton realizes any object will mass exerts an attractive gravitational force F on all other objects having mass F = GMm/ r^2 M- mass of one object m- mass of other Four important discoveries Galileo did with his telescope and how some of them supported the heliocentric model discoveries: moon has craters and mountains, sunspots and the rotation of sun, satellites of jupiter, phases of venus 3 Wednesday, April 20, 2016 Concept of mass and weight. How your mass change if you are on the Moon? How is your weight change is you are on the Moon? your mass is constant , your weight changes Chapter 2– Light and matter Considering the color of a star, can you tell which star are cooler and which are hotter and why? cooler bodies radiate more at longer wavelengths and are redder hotter bodies radiate more at shorter wavelengths and are bluer If we increase the temperature of a body by 3 times, how is the total radiative flux change? Use F = T^4 If we increase the temperature of an object what happens to the wavelength of the maximum or the peak of emission? Use λmax = 0.29/T What does the temperature means regarding thermal energy in a gas? Average kinetic energy of a gas proportional to molecular mass and the square of the speed Is the velocity of propagation of a electromagnetic wave (light) wavelength dependent? v/c = Δ lambda/ lambda = (lambda shift - lambda rest)/ lambda rest delta lambda = change in wavelengthand lambda = wavelength — so yeah What is the velocity of propagation of a radio wave? Velocity of propagations of a Gamma ray? Which of the two propagate (travel) faster? Energy of a radio photon (or radio wave) Energy of a Gamma photon (or Gamma wave) Use: Eph =h f =hc/ Which of the two photons has more energy? radio photon has long wavelengths and low energy gamma ray photon has short wavelengths and HIGH energy 4 Wednesday, April 20, 2016 What is Doppler red-shift. What does it tell you about its velocity and the direction is moving? If a star is coming towards the observer how are the spectral lines shifted? If the star is moving perpendicular to the observer how are the spectral lines shifted? if the object is rotating, the side approaching the observe will be blue shifted and the side moving away form the observer will be red shifted What can we learn from spectral analysis? Composition, temperature, line-of-sight velocity, rotations rate, pressure of a gas and the presence of magnetic field (Zeeman effect). Chapter 3– Telescopes Why astronomers build bigger telescopes? Any advantage of having bigger telescopes? larger lens/mirrors increase both the light-collecting area, and angular resolution What is the dependence of the diameter of a telescope with the light gathering power? larger diameters have larger collecting areas which can ultimately gather a greater amount of light in a shorter time What is the dependence of the diameter with the angular resolution of a telescope? larger diameters are capable of taking images with greater detail If the separation between two star in a binary system is much smaller that the resolution of the telescope, will you be able to see those two star separated? Why? if the diameter of lens/mirror (aperture) is small it would be very difficult to see two SEPARATE stars Can you see the craters on the moon with the naked eye? Why? no because the turbulence in the terrestrial atmosphere distorts the image of lunar craters Why telescopes for the x-rays and gamma-rays need to be in space? because telescopes in space are no affected by the blurring effect, absorption of light, and/or light pollution of the terrestrial atmosphere How a CCD stores an image in a computer? the pixels in CCDs are sensitive to light and when light strikes a pixel, it will develop an electric charge proportional to the intensity of light; the charge in each 5 Wednesday, April 20, 2016 pixel is read by the electronics controlled by a computer and stored as an array of numbers What is the advantage of the Hubble telescope? Hubble telescopes are in space so turbulent air flow in earth’s atmosphere doesn’t distort the view Chapter 3– Telescopes cont. Why telescopes for the UV, X-rays and gamma-rays need to be in space? Some wavelength of light other than radio and visible do not pass through Earth’s atmosphere. Much sharper images are possible because there is no atmospheric turbulence. 
 No light pollution from light scattered in the terrestrial atmosphere allows long exposure for recording very faint objects Do X-rays telescope use regular mirror? no, they use a special mirror; Mirrors are arranged to focus X-ray photons through grazing bounces off the surface Do gamma ray telescope use mirrors? Focusing gamma rays is extremely difficult. 
 For the Fermi telescope, the detectors are scintillation detector, array of 12 crystals (Sodium Iodide) 
 The detectors are arranged in a 3-D matrix. That allow to determine the direction from where the gamma ray came from What is the advantage of combining the light (or signal) from two or more telescopes (Radio telescopes)? The resolution obtained is equivalent to the resolution of a single large radio telescope of an equivalent diameter equal to the separation. increase in angular resolution What is Interferometry? a technique that consist in linking two or more telescopes and combining the signal from them. Chapter 5 – The Earth and Moon 6 Wednesday, April 20, 2016 What is the configuration of the positions of the Sun and Moon for the spring tides? For neap tides? spring tides- new moon and full moon neap tides- first quarter and third quarter moons (sun and moon 90 degrees from each other) How many high tides are in 24 hours period? Why? there are always two bulldogs on the earth - 2 high tides and 2 low tides every 24 hours Why the tidal effect of the Sun is smaller than the tidal effect of the Moon? the moon has a larger differential gravitational attrition because although the sun’s gravitational attraction on the earth is larger than the moon and has a greater mass, it is a lot farther than the moon How do we know about the Earth interior? How are the P and S wave used? we know about interior by studying how seismic waves travel through it - earthquakes generate P (pressure) and S (shear ) waves; P waves travel through liquid outer core by are selected by the core and S waves travel in the mantle but not through the liquid core Equations for the escape velocity and the molecular velocity Vesc = 11.2 sqrt mass of body/radius of body Vmol= 0.157 sqrt temp in K/ molecular mass in H atom masses What is minimum ratio of escape velocity to mean molecular velocity so gases are retained in the atmosphere of a planet? if a planet’s escape velocity is at least ~6 times greater than the mean molecules velocity, the molecules of that type will not escape Which gases may leave an atmosphere faster? Why? What cause the depletion of ozone in the atmosphere? CFC when choroflourocarbons (CFC’s) combine with O3, they destroy the O3 CFC dissociates in the upper atmosphere by solar radiation and releases chlorine which combines with O3 and forms O2; the Cl acts a a catalyst and participates in the reaction but it is released a the end of the reaction 7 Wednesday, April 20, 2016 What is the ozone hole and where it is located hole is over Antarctica How can we explain the large density of the core of the Earth and the terrestrial planets? high central density suggests the core is mostly nickel and iron What is differentiation? earth was molten, allowing high density material to sink to the core; the material is still at a high temp ~5000K What were the sources of heat that made the Earth to rise its internal temperature and melt? interplanetary debris and radioactive decay Name the two main greenhouse gasses present in the atmosphere of the Earth? CO2 and H20 vapor Name the two main gases in the atmosphere of the Earth N and O2 Why the Moon has been able to preserve the impact crater? lack of atmosphere and water preserves surface features Why the Moon does not have an atmosphere? very small - doesn’t have necessary Vesc and Vmol ratio What are the lunar maria (mare) and what caused them? younger areas on mantle material, darker areas resulting from earlier lava flow How do we explain the presence of Earth’s magnetic field relatively fast rotation of the planet electrically conducting metal core = dynamo effect What are the two conditions that may explain the formation of magnetic field in a planet? same as above 8 Wednesday, April 20, 2016 Does the Earth meet these two conditions? yes What causes the aurora? Describe the process that produces an aurora charged particles are ejected from the sun - in a solar flare a lot of them are ejected and collide with the earth’s magnetosphere, the particles either the field and are directed toward the poles the particles precipitate near the poles colliding with earth’s upper atmosphere, the gases in the atmosphere are excited and emit light; the colors of the auroras depend on the gasses and the altitude at which they are excited. How the Earth’s magnetic field and the ozone layer protect life on Earth? ozone layer absorbs UV light What are the theories of formation of the Moon? Which is the most accepted one? earlier theories— both earth and moon formed together from same material and/ or moon formed somewhere else and was captured by the earth most accepted- impact theory a mars-sized body collided with he molten earth and there was an exchange in material- parts of the earth’s mantle were ejected in the collision and later condensed and formed the moon Chapter 6 – The Terrestrial Planets Regarding size (diameter) how is the Earth compared with Venus, Mars and Mercury? size from biggest to smallest — earth - venus - mars - mercury What is the problem for determining the rotational period of Mercury and Venus? How is the rotational period determined? they are the inner most planets mercury has a max angle of 28 between sun and venus has a max angle of 47 — this angle = elongation mercury- 59 days venus- -243 days (retrograde) How dense is Venus atmosphere compared to Earth? atmospheric pressure for venus is 90 and earth is 1 What is the main gas in the atmosphere of Venus? 9 Wednesday, April 20, 2016 CO2 Clouds in Venus atmosphere: What is the composition of the clouds? sulfuric acid What are the main difference between terrestrial planets and Jovian planets? jovian - giant, more satellites, farther from sun Which of the terrestrial planets does not have an atmosphere? mercury What are the similarities between Mars and Earth regarding rotational period, inclination of rotational axis? axial tilt - 24 degrees and rotation period is 1.03 days which is ~ same as earth How is the density of the atmosphere of Mars compared to Earth? atmospheric pressure of mars is .007 and earth is 1 What is the main gas in the atmosphere of Mars? CO2 Main differences between the north and south hemisphere in Mars north hemisphere is flat and has rolling volcanic planes and few craters south hemisphere is heavily cratered and older Mars is called the Red planet. What gives the red color to the surface of Mars? iron and oxygen in the atmosphere combine to give the red color Origin of Valles Marineris probably due to stretching and cracking when thoraces bulge formed Which planet has the largest volcanoes in the solar system? Name one. Mars - olympus mons What is the evidence of flow of liquid water on Mars in the past? Runoff and outflow channels ~4 billion years ago mars had a thicker atmosphere and warmer surface so it could probably maintain liquid water 10 Wednesday, April 20, 2016 runoff channels - found in souther highlands, extensive river systems, carried water from highland to valleys outflow channels - caused by flooding, found at the equator, formed long ago Any recent discovery of water ice a few centimeter under the surface of Mars? Phoenix lander found frozen water under the surface near the poles a trench was carved by the scoop of the phoenix lander; the small lumps of light material inside is water ice that sublimated soon after being exposed Recent discovery of salty water running down the slopes of craters: Gullies salty water may stay in liquid phase for a short time due to its lower freezing point Recent discoveries of Curiosity mission: Equivalent of a dry river bed containing smooth surface rocks and pebbles. Layers of flat rocks Did the Viking experiment found clear evidence of microscopic life? What are the arguments in favor or arguments to reject the evidence? revealed a process SIMIAR to metabolic reactions but results were not consistent with other experiments - no convincing data Did the analysis or the Martian meteorite gave clear evidence of microscopic fossil life? What are the arguments to support and the arguments to reject the possible presence of fossil life What is a “splosh” crater? What causes the unusual shapes of the slopes? Venus axial tilt. What is unusual regarding the axial tilt? 177.4 degrees - probably caused by collision Venus rotational period. What is unusual regarding the rotational period? retrograde - probably caused by collision Meecuryy Venus Earth mars the smallest and slightly smaller than largest of the terrestrislightly bigger than innermost planet earth , also an inner planets mercury, farthest planet terrestrial from the sun 11 Wednesday, April 20, 2016 Mercury Venus Earth mars no atmosphere or surface atmosphere =90 surface atmosphere=1 atmospheric pressure= satellites no satellites has the moon .007 and has 2 small moons (Phobos and Deimos) surface temp 100-700K temp 730k 180-270K axial tilt= 0 axial tilt= 177.4 degrees axial tilt- 23.4 degrees axial tilt= 24 degrees rotation period=59 days rotation= -243 rotation= 1 day rotation = 1.03 days (retrograde) large number of impact mostly CO2, thick mostly N very thin atmosphere, craters on the surface, clouds of sulfuric acid mostly composed of old surface, no plate make seeing surface CO2, rocks are rich in tectonics, has cliffs impossible, shield iron, the combo of iron (scarp)- result of surface volcanoes and oxygen give the red cooling, shrinking and color, largest volcanoes splitting at this time in the solar system - olympus mons, liquid water once existed Chapter 7 – The Jovian Planets Which of the Jovian planets have rings? all jovian planets have rings Which is the less dense of the Jovian planets? What is its density? Saturn What is the Great Red spot? Where is it located in the disk of the planet? Jupiter - close to the equator How is the mass of Jupiter compared to the mass of the other planets Jupiter is most massive planet 12 Wednesday, April 20, 2016 Which of the Jovian planets have the strongest magnetic field? Jupiter What can be find in the interior of Jupiter and Saturn that may explain why they have a strong magnetic field? they have metallic hydrogen -electrically conducting core How that affect the presence of magnetic field in Jupiter and Saturn? contributes to a a electrically conducting core - one of the elements needed for a magnetic field ( the other is fast rotation) Which Jovian planet emit the strongest low radio frequency radio emission, easily detectable from low frequency ground-based radio telescopes? Jupiter How can we explain the lower density of Helium in the atmosphere of Saturn compared to Jupiter? saturn has less helium (7%) than Jupiter (14%) — How is that related to the generation of internal heat in Saturn? Saturn generates some heat due to the gravitational heating of liquid helium droplets falling into the liquid Hydrogen - this may account for the depletion of the outer layers of He. What is the tilt angle of Uranus rotational axis? Does Uranus have seasons? yes - extreme seasons b/c 98 degree tilt What explains the blue color in the atmospheres of Uranus and Neptune? methane gives blue color Have we ever witnesses the collision of the comet with a Jovian planet? in 1993, the comet Shoemaker-Levy 9 collided with Jupiter and broke into 23 pieces - strong tidal forces caused it to break apart Chapter 8– Satellites, rings, plutoids How do we explain the presence of active volcanoes in Io 13 Wednesday, April 20, 2016 the elliptical orbit of Io causes tidal heating which squishes and stretches as it orbits Jupiter - this process releases heat and rises the internal temperature ultimately providing various volcanoes The mechanism that generate the energy that produce Io’s volcanic activity elliptical orbit — tidal heating How do we explain the presence of an ocean of liquid water under the frozen surface of Europa tidal heating due to the elliptical orbit of Europa allows thermal vents to bring up the heat from the core and keeps the interior temperature above freezing point What causes the elliptical orbit of Io, Europa and Ganymede? there is an elliptical orbit because of orbital resonance between the orbital period of Io, Europa, and Ganymede- they line up every 7 earth days (resonance), tugging in the same direction distorts the orbit form a circle to an ellipse Which satellite in the solar system as the most volcanic activity Io What is the composition of the lakes found on Titan’s surface? liquid methane and ethane Do we expect to find liquid water on the surface of Titan? Titan has a icy mantle over a rocky core, there is a layer of liquid water under the ice What type of chemical compounds (or molecules ) are in found in the atmosphere of Titan? nitrogen, methane, argon, hydrocarbons, clouds of methane and Nitrogen ices How many of the Jovian planets have rings all of them The rings of which planet can be seen even with a small telescope? saturn Are the rings solid? 14 Wednesday, April 20, 2016 not solid object, comprised of many small solid particles in orbit around the planet - water ice is primary constituency Do the particles in the rings follow Kepler’s law? yes , inner particles revolve faster than those further out, rings are not rotating as a solid body, rather individual moonless are revolving around the planets What is the size of particles in the rings? can range from grains to large boulders the size of a house What causes the gaps in the rings of Saturn the gravitational attraction (resonance) of the satellites clears gaps in rings What happens to a body when it gets close to the Roche limit of a planet ? the Roche limit is the closest distance an object can come to another large mass object without being pulled apart by tidal forces - so if it gets to close, it pretty much explodes Where are the rings located respect to the Roche limit: inside or outside the limit? inside the Roche limit How is Pluto classified now? a dwarf planet Is Pluto the only body in the Kuiper belt? no How many satellites has Pluto? 5 satellites How far is Pluto from the Sun? 40 AU Features found in images of the surface of Pluto (New Horizon). Lots of impact craters? What is the density and composition of the objects in the Kuiper belt. most objects in Kuiper belt composed of “ices” mainly methane, ammonia, and water ices CRATERS? Regarding density and constitution, do they look similar to the terrestrial planets? 15 Wednesday, April 20, 2016 How far is the Kuiper belt from the Sun? 30-50 AU Ch. 4 Formation of the Solar System Using a ground-based telescope, can we see the nucleus of a comet? How big is a comet nucleus? nucleus is just a few km in diameter, it is too small to be resolved with telescopes, nucleus has been imaged by spacecraft only What is the origin of an iron-nickel meteorite? they are fragments of a larger body - the body was large enough to generate internal heat and went through the differentiation process - heavier material sunk to the core- collisions broke the large body, exposed the central part (core) from which the smaller pieces came from What is the origin of the material that creates a meteor shower? it is called a meteor when it enters and burns in the earth’s atmosphere - most are the result of the earth passing through the orbit of a comet which has left debris along its path Why it is easier to detect big exoplanets located closer to the star? because of their bigger mass and close distance to the star, they produce larger radial velocity changes in the star which are reflected in a large Doppler shift of the star Why is that the contraction of an interstellar cloud of gas and dust take the shape of a flat disc? centrifugal forces perpendicular to the rotational axis provided a push outward that resisted the contraction. the forces in the direction of the rotational axis pointing away from the center are small . the gravitational forces along the rotational axis are not opposed by any other forces What is the most accepted hypothesis for the formation of the solar system Nebular theory 16 Wednesday, April 20, 2016 our sun and planets originated from collapse of an interstellar cloud of dust and gas because of a pressure wave generated from a supernova explosion or a density wave in the galaxy compressed the cloud and triggered the collapse - after that, the cloud began contracting under its own gravity and developed a disk - reason: conservation of angular momentum How many exoplanets have been detected so far? A few tens? A few hundreds? 961 detected by Kepler spacecrafy Any detection of Earth-size planets in the habitable zone? yes - venus? What is the habitable zone? the region around a star where water can exist in liquid form Ch. 9 The Sun What is the approximate rotational period of the Sun? 25 days (equator) & 36 days (poles) What is the approximate mean density of the Sun (1410 kg/m3)? 1410 kg/m^3 What is the approximate surface temperature of the Sun 5780K How do we determine the luminosity of the Sun (L=Flux* 4 π R2)? L=Flux* 4 π R2 What is the temperature of the core of the Sun? 15 million K What mechanism produce the energy in the core of the Sun? convection - solar granulation? Minimum temperature needed for the fusion of H into He at least 10^7K because merging nuclei requires high speed - high temp = high speed 17 Wednesday, April 20, 2016 What type of spectrum emits the Sun? the solar spectrum which has thousands of absorption lines How can we see the solar corona? during a total solar eclipse How long does it take for the electromagnetic radiation to reach the Earth? 8 minutes How long does it take for the solar wind and particles ejected from the Sun to reach the Earth? about 3 days Ch. 10 Measuring the Stars How can we determine the radial motion of a star? measured through Doppler shift of emission/ absorption lines How can we determine the transverse motion of a star? need to know proper motion and then the distance to the star The two axis in the HR diagram: Luminosity and temperature luminosity is the amount of radiation leaving a star per unit time Where are the low and high temperature stars located in the HR diagram? Where are the low mass and high mass located? Where are the high radius and low radius stars located in the HR diagram? temp increases from right to left, luminosity increases going up How can you determine the luminosity L of a star (in solar units) respect to the Sun? If we know the Radius or the Temperature respect to the Sun? Remember: Lstar= (Rstar/ Rsun)2 * (Tstar/Tsun)4 * Lsun 2 4 L = (R /R ) * (T /T ) * L star star sun star sun sun 18 Wednesday, April 20, 2016 How important is the mass of a star? Parameters of a star determined by the mass of a star: Luminosity, radius, surface temperature, lifetime, evolutionary phases A star of smaller mass lives a shorter or a longer life respect to a large mass star? more mass = shorter lifetime Ch.12/13- Stellar evolution How long will take for the Sun to convert all the H into He until all the H is used up? ~10 billion years (its main sequence lifetime) — this process is called core hydrogen burning Temperature necessary to fuse He? Temperature necessary to fuse Carbon? helium fuses into carbon at > 10^8 K How long will the Sun stay in the main sequence? ~10 billion years Where does the Sun moves in the HR diagram once it has used all the H? To what area of HR diagram? it moves up the red giant branch 0 ascension up this takes ~100 million years (top right) When the Sun moves off the main sequence, does surface temperature increases or decreases? What happens to the diameter ? it expands and cools Why the Sun cannot fuse carbon? because carbon nuclei has 6 protons which repel each other A TON so it would need a crazy high temperature, once the core reaches 10^8K, helium “ignites” to make carbon causing the temperature to rise sharply in a runaway explosion - helium flash What happens to the Sun once it use all the H and He and end up with a core of carbon? 19 Wednesday, April 20, 2016 the core expands, density drops, and equilibrium is re-established, core structure is now readjusted during helium core burning and total luminosity is actually decreased, during core helium burning, the star is on the horizontal branch What is a planetary nebula? last stage of the evolution of a star with a mass close to the sun, they emit line radiation (hot low pressure gas) but in size are much smaller than the emission nebulae What is a white dwarf? What is the chemical element that compose a white dwarf? an object about the size of the earth - carbon and oxygen Why a star more massive than the Sun can fuse heavier elements such as carbon, oxygen, neon? gravity squeezes and heats the core. the temperature needs to increase enough to be able to ignite carbon - around 600 million K- then it will continue fusing oxygen, neon, et. What happens when a massive star try to fuse iron? there is no more source of energy and the iron fusion takes energy from the core, the pressure that support that star’s core is lost, and the core quickly collapses under its own weight What is the final body resulting from the collapse of a star of one solar mass? white dawrf Final body of a star with more than 1.4 solar masses but less than 3 solar masses? neutron star Final body for a star with more than 3 solar masses? Black hole Size of a white dwarf? Size of a neutron star? Size of a black hole? white dwarf - diameter 12,000km neutron star- 20km across black hole —- unknown 20 Wednesday, April 20, 2016 What is a pulsar? rotating neutron star with a strong magnetic field What would happen to the Earth’s orbit if the Sun could collapse into a black hole? the earth would be at the same distance, at 1 AU a solar mass black hole, it will feel the same gravitational attraction from the Sun at 1AU How it is possible to estimate the mass of the massive black hole in the center of the Milky Way? newton version of Kepler 3rd law! Mbh= a^3/P^2 Ch.14 The milky way galaxy What are the relationship between the two parameters that makes the Cepheids and RR Lyrae useful to measure distances? there is a relationship between he pulsation period of these variables and its luminosity Flux ~ luminosity/distance^2 How Hubble was able to determine the distance to the Andromeda galaxy? he discovered cepheids in the “spiral nebula” in Andromeda and then derived the distance to andromeda, and showed that it was external to our galaxy (~2.5 million light years away) What method was used to determine the distance to the globular clusters in the MW? Why finding the location was important? What tracers are used to trace the spiral structure in the MW? 1- O and B stars, in other galaxies, spiral arms contain mostly hot O and B stars 2- giant molecular clouds - if spiral arms are associated with star formation, then they must also be traced out by the locations of GMCs 3- neutral hydrogen - in other galaxies, HI traces the spiral arms very well What mechanism produces the 21 cm radio emission only cold low density clouds of hydrogen will emit radio emission at a wavelength of 21cm Why is the 21 cm suitable to determine the spiral structure of the disk in our galaxy? 21 Wednesday, April 20, 2016 The right panel shows M83 in the 21-cm radiation of neutral hydrogen again revealing its spiral structure. by looking at the distribution of HI in the sky and measuring doppler shifts in the 21cm emission line, we can map out the spiral structure in the galaxy What is the evidence of dark matter in the outer part (beyond 15 kpc) of the MW? use gravitational lensing which bends light of the background star because of its gravitational field . the light from the background star is focused or lensed by this effect and the star appears brighter What are the possible candidates to explain the existence of dark matter? white war stars, very low mass stars (red dwarfs), brown dwarfs, neutron stars, black holes How do we know that there is a black hole in the center of our galaxy? because we have observed the center of the milky way which shows movement of stars around a central supermassive, what we believe to be, a black hole How many solar masses are estimated to have the black hole in the center of the MW? 4 million solar masses 22


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