Review for Exam 1 How do you measure angular distances between stars and how do you measure angular sizes of objects such as the sun, the moon, etc? ● MeasIf you want to learn more check out sonny 2017 guide
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Don't forget about the age old question of What is its surface temperature in degrees Kelvin?
ure angular distances between stars and angular sizes of objects using the small angle formula. What is an arc minute and an arc second. ● Degrees measure angles! ● A degree is 1/360 of a circle ● A minute of an arc is 1/60 of a degree ● One second of an arc is equal to 1/60 of a minute ● There are 3600 arc seconds in a degree What is the celestial sphere, the celestial horizon, zenith, north celestial pole, celestial equator? ● Celestial sphere: Term used to describe appearance of the sky ● Zenith: Point on the celestial sphere directly above your head ● Celestial Horizon: The great circle located 90 degrees from the zenith. It divides the celestial sphere into an upper (visible) and lower (non visible) half. ● Celestial equator: the circle midway between the poles. Divides the celestial sphere into northern and southern halves. ● Meridian:Passes through the south pole, north pole and the zenith. The half of the circle above the horizon divides the sky into eastern and western halves. ● North Celestial Pole: Point on the celestial sphere directly above the Earth’s North Pole ○ Has an altitude = to the observer’s latitude. ○ If you travel northward to higher latitudes, the NCP climbs higher which causes the circumpolar region to grow in size. What is latitude, longitude, altitude, azimuth, declination, right ascension? ● Latitude: Angle between the equator and a geographical location ● Longitude: Angle east or west, around the equator to the point nearest on the earth’s equator ● Altitude: The Angular distance above the celestial horizon and corresponds to the latitude in the terrestrial coordinate system ○ The horizon has an altitude of 0 degrees and the zenith has an altitude of 90 degrees ● Azimuth: The angular distance measured from North eastward around the celestial horizon to point directly below the chosen location (corresponds to the longitude in the terrestrial coordinate system) ○ East= 90 degrees ○ South= 180 degrees ○ West= 270 degrees ○ North= 0 degrees or 360 degrees ● Declination: Equal to the angular distance of a star from the celestial equator ● Right Ascension: Angular distance measured eastward along the celestial equator from the vernal equinox to the point on the celestial equator nearest the star’s position (measured in hours) ○ 1 hour of RA = 15 degreesWhat is the main disadvantage of the Horizon System ● Does not work if two people aren't together Do Altitude and Azimuth depend on time and location ● Yes. Do Declination and Right Ascension remain the same throughout the night? ● Yes, because the Vernal Equinox (position of the sun the first day of spring) moves with the stars, so RA and Dec remain the same throughout the night. How do the stars appear to move in the sky as a result of the earth’s rotation. ● Earth rotates eastward (from west towards east) ● Stars appear to move westward ● If we are facing NORTH the motion appears counterclockwise ● If we are facing SOUTH the motion appears clockwise ● Circumpolar motion ○ Circumpolar stars never set ○ Stars in the region centered near polaris move counterclockwise on circles that never carry them below the horizon. This region is called the circumpolar zone ○ Stars outside the circumpolar zone move on circles that carry them below the horizon ● Motions of stars seem to be caused by the rotation of the celestial sphere about an axis that passes through the celestial poles ● Appearance of sky and the motions of the stars also depend on the latitude of where you are observing. How does the sun appear to move in the sky due to the earth’s orbit around the sun? ● Annual motion of sun is primarily eastward ● Ecliptic is tilted to the celestial equator ● Angle between the equator the the ecliptic is 23.5 degrees ○ So the sun’s declination varies from +23.5 degrees and -23.5 degrees How far down do you have to move in order to have sunlight? ● The degree of the tilt of the earth (23.5 degrees) ● 66.5 degrees or south you will have some day and some night. What is the ecliptic? ● The Ecliptic is the path the sun follows among the stars How fast the sun moves eastward among the stars? What are the zodiac constellations? ● The length of time it takes for the sun to move through the constellations and return to the same spot is defined as the year. Because there are 360 degrees in a circle and 365 days per year, the sun moves with respect to the stars at a rate of slightly less than 1 degree per day. ● Zodiacs: Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini, Cancer, and Leo. 6 What causes the occurrence of seasons on the Earth? ● The tilt of the earth What is significant about the solstices?● Summer Solstice: The point on the ecliptic where the sun’s declination is most NORTHERLY ● Winter Solstice:Point on the ecliptic where the sun’s declination is most SOUTHERLY More on equinoxes: ● The points where the sun crosses the celestial equator and has zero declination are called the autumnal equinox and vernal equinox. ● Vernal Equinox is the point at which right ascension is measured What is faster the solar day or the sidereal day? ● Solar day (24 hours) is longer than the sidereal day (length of time it takes for a star to return to the meridian). Because the sun appears to move eastward relative to the stars, it recrosses the meridian later than the star What is the max point of sun during the day called? ● Solar noon What causes the phases of the moon? ● Light reflection ● The phases of the moon depend on how much the side turned toward us is illuminated by the sun ● Phased determined by the position of the moon relative to earth and sun. What way does moon move? How long? ● Eastward ● Sidereal month: 27.3 days- the length of time it takes for the moon to return to the same place among the stars ● Synodic month: 29.5 days - time it takes for moon to return to same position relative to the sun. ● The inclination of the moon’s orbit is about 5 degrees Full moon vs New moon: ● Full moon: Moon is opposite the sun in the sky so that we are nearly between the moon and sun ● New moon: Moon is nearly between us and the sun, so that the moon and sun are close to each other. Waxing vs waning: ● Waxing means growing larger ● Waning means getting smaller What are the angles of the earth, moon and the sun at full moon, new moon, a quarter moon. In order of Earth-Moon-Sun... ● Full moon: 0 degrees ● New moon: 180 degrees ● Quarter moon: 90 degrees *This was phrased really awkwardly. I assume if this is on the test he’ll be clearer about what he wants. Retrograde● When a planet moves eastward it is said to be prograde or direct. ● Retrograde: At regular intervals a planet appears to reverse its direction of motion and for a time moves towards the west with respect to the stars What is precession of the earth’s axis and how long it takes to complete one cycle. What are the consequences of this precession? ● The precession of Earth’s axis is its very gradual rotation as the Earth itself turns (like a top spinning but much slower). It takes 26,000 years to complete. ● (My interpretation of) the consequences of this procession is that our viewpoints are based upon our temporary position with both the poles and equator therefore they vary approximately every 78 years. Application of the small angle formula: Something which is 500 km away has an angular size of 5 seconds of arc. Approximately how tall is it? 5 = 200,000 h/d d is 500,000 meters. h is 12.5 m **Not sure where 200,000 came from. I’m finding 206,265 a lot--maybe he rounded? It would make sense that it’s a constant because the other constant we used in its place was 57.3. What is believed to be the contribution of the Greek astronomer Aristarchus? ● He showed that it is possible to use geometry to find the distance of the moon and the relative distances of the moon and sun. By doing so he showed that the universe is enormous compared with the size of the earth. ● He also proposed that the sun, not the earth, is the center of the universe. What are the reasons why the other astronomers rejected his Heliocentric model? ● The earth couldn't be spinning rapidly on its axis and moving at great speed about the sun without consequences. What quantities did he calculate? ● He proposed the small angle formula. ● The distance to the moon How did Eratosthenes determine the size of the Earth? ● Used geometry ● Found the difference in the altitude of the noonday sun at Syene and Alexandria. He realized that this is the same as the difference in latitude of the two cities. Which allowed him to find the ratio of the circumference of earth to the distance between Syene and Alexandria. What evidence did Aristotle offer for his argument that the Earth is a sphere? ● Falling objects move toward the center of the earth ● The shadow of the earth (best shown during the eclipse) is always circular ● Some stars can be seen in egypt but not in Greece An astronaut lands on an unknown planet. After walking a distance of 50 km toward the north pole of the planet, she notices that the pole star for that planet is 1 degree higher in the sky. What is the circumference of the planet?● 360/diff in degree = x/diff in distance ● ● 360/1 = x/50 ● ● 18000 9 What were epicycles and why they were used in Ptolemy's model of the solar system? Why are there two models? ● Ptolemy: Constructed one of the best geocentric models ● Ptolemy’s model is geocentric (earth at the center) ● The epicyclic model perfected by Ptolemy used combinations of circular motions to reproduce the motions of the planets. This model could predict the positions of celestial objects with such accuracy that it was used for nearly 1500 years. Deferent and epicycles in the geocentric model: ● The Ptolemaic model accounted for the apparent motions of the planets in a very direct way, by assuming that each planet moved on a small sphere or circle, called an epicycle, that moved on a larger sphere or circle, called a deferent What are Copernicus’s main contributions to astronomy? What did he believe? ● Introduced a mathematical model for a Heliocentric universe. The Sun is at the center of the universe ● Diurnal motion of celestial objects What are Tycho Brahe’s main contributions to astronomy? ● Brahe: Excellent observational astronomer; Recorded superb naked-eye positions of the planets ● Collected a ton of data. Which are Kepler's Laws of Planetary Motion? ● 1st law: the planets move on elliptical paths with the Sun at one focus (and nothing at the other) ● 2nd law: a planet moves so that a line drawn between the planet and the Sun sweeps out equal areas in equal amounts of time. This means that the product of transverse velocity and distance from the Sun remains constant as a planet moves about the Sun. (the point is that the planet moves faster when it’s near the Sun and slower when it’s farther away from the Sun). ● 3rd law: The square of the sidereal period is proportional to the cube of its average distance from the Sun. (P^2=a^3 where P=sidereal period of planet in years, a=semimajor axis of planet in AU). Sidereal period=time (in years to complete one orbit). Semimajor axis=half of major axis/line drawn thru long part of ellipse. This is used to calculate the orbital period of a planet from its distance or vice versa. 3 A hypothetical planet orbits the sun a distance of 10 Astronomical Units. What is its orbital period? 31.62277766017 years (the square root of 1000). P^2=a^3. a=10. P^2=10^3. P^2=1000. P=sqrt1000 31.6227766What is retrograde motion of the planets and how can it be explained? How does the ancient geocentric model explain it?**NOT DONE BUT I WANNA TRY TO DO OTHER QUESTIONS ● Retrograde motion of the planets refers to the regular shift of a planets’ orbital course where said-planet will appear to move westward relative to the stars instead of eastward and make an ecliptic that can vary each time. ● Also acknowledge that retrograde can refer to the PERCEPTION of the planets moving backwards in the sky--Earth moves faster than Mars so sometimes as we’re orbiting the sun we’ll pass Mars and it’ll seemingly be moving behind us. What are the main Galileo's contributions to astronomy? ● Father of experimental science; First to point a telescope (which he built) toward the sky in 1609 ○ Observed in telescope: ○ 1. Moon craters and mountains ○ 2. Sunspots and the rotation of the Sun ○ 3. Moons of Jupiter ○ 4. Phases of Venus Galileo and his experiments: ● Moving balls: He found that the distance a ball travels is proportional to the square of the time it has been in motion. ● This experiment led him to conclude that motion is a natural state: once an object is set in motion it will continue that motion until something stops it. Descartes and Inertial Motion: ● Descartes believed that all changes in motion resulted from collision with particles called “corpuscles” ● Inertial motion: the motion of an object when there are no unbalanced forces acting on it. Which are the Newton’s laws of motion? What is acceleration? How does the force of gravity depend on the distance between two bodies and their masses? ● Law of inertia: An object remains at rest or continues in motion at constant velocity unless it is acted upon by an unbalanced external force ○ Inertia ○ Velocity: speed of an object and the direction it moves in, a vector ○ Acceleration: The rate velocity changes with time ,a vector. ○ Mass: a measure of the inertia of a body- its resistance to acceleration. ○ Momentum: mass multiplied by velocity equals the product of momentum (p = mv) ● Law of force: When a net force acts on an object, it produces a change in the momentum of the object in the direction in which the force acts. ○ Force = mass times acceleration (F=ma) ○ Force is a vector ● Law of Action and Reaction: When one body exerts a force on a second body, the second body also exerts a force on the first. These forces are equal in strength, but opposite in direction.○ Forces always occur in pairs. Whenever one body exerts a force, the first body feels a force exerted on it by the second body. The two forces are equal in magnitude but opposite in direction. ● Gravity ○ Gravity is responsible for the motions of both planets and falling objects near earth ● Centripetal acceleration: the acceleration towards the center of the circle ○ Caused the path of the orbiting object to continually bend away from the straight path it would follow if no force were acting. ● Centripetal force (needed for centripetal acceleration) acts towards the center of the circle ● The centripetal acceleration required for circular motion can be calculated if the orbital speed and distance of the body are known. ● Newton used the equation for centripetal acceleration and Kepler’s third law to show that the force required to keep the planets in orbit must vary with the inverse square of distance from the sun. ● Law of universal gravitation: every two particles of matter in the universe attract each other with a force that depends on the product of their masses and the inverse square of the distance between them ○ Fg= GMm/d^2 ○ For spherical bodies, the distance to be used in the law of gravitation is the distance between the centers of the bodies. What is the direction of the force required to keep an object in a circular orbit? What is the wavelength, the frequency and the velocity of an electromagnetic wave? How are they related? ● Wavelength: the distance between successive crests of the wave ● Frequency: the rate at which wave crests pass a fixed point ● Frequency is usually given in number of wavelengths per second or hertz ○ c= yf or f=c/y ○ C (speed of light) = 3 x 10 ^8 = 300000000 ○ f= frequency ○ y= wavelength ● Energy Flux of a wave is the rate at which the wave carries energy through a given area ● Electromagnetic wave: oscillating electric and magnetic fields produced by accelerating electric charges. All electromagnetic waves travel at the speed of light. What distinguishes them from each other are their wavelengths and frequencies. ○ Waves with small wavelengths, such a gamma rays, have high frequencies. ○ Waves with large wavelengths, such as radio waves, have low frequencies. What is the Doppler effect? The equation? ● Doppler effect: A change in frequency and wavelength of a wave that is emitted by or reflected from a body in motion in respect to the observer who measures the waves. ● When the observer and the source of the waves are MOVING TOWARD each other wavecrest arrive more often than they would if there was no motion. ○ Thus the observed frequency is higher and the wavelength is shorter. ● If source and observer are MOVING APART, the observer measures a lower frequency and a longer wavelength. ● Change in wavelength/original wavelength= speed approached/speed of light Reflection and refraction:● Reflection: the bouncing of a wave from a surface. When a wave is reflected its new direction depends on the direction of the incident wave and its orientation to the reflecting surface. ● The reflectability of a wave describes its ability to reflect electromagnetic waves. ● Refraction: bending of light when it passes from one material into another. ○ Ex a straight meter stick appears to bend at the point where it emerges from water ● Refraction occurs because the speed of light depends on the material through which it is passing ● The speed of light in a material is described by index of refraction. ○ The greater the ratio of refraction, the more a wave is bent ● Dispersion: When a beam of light falls on a prism it is separated according to wavelength to form a spectrum. The separation of light according to a wavelength is called dispersion ○ Occurs because the index of refraction in glass depends on wavelength. ○ Within the visible spectrum, the index of refraction of violet light is greatest. Red light is smallest. What are the various types of mirrors and lenses? How do they work? Optical telescopes use lenses and mirrors to bring light to a focus. The lens or mirror used to focus the light is called the objective of a telescope. ● Refractor: a telescope in which the objective is a lens. ○ Focal point of a lens is the spot at which parallel beams of light striking the lens are brought to a focus and cross. ○ The distance of a lens to its focal point is called the focal length ● A crude lens made from two prisms: beams refracted by the two prisms are focused at the point where they cross. ● The focusing of light by a lens: All parallel beams of light at the focal point of the lens, which is located one focal length behind the lens ● Focal length and the curvature of the lens: Highly curved lenses have short focal lengths. Slighting curved lenses have long focal lengths. ● Reflector: telescope in which the objective is a mirror ○ Focal length is distance from mirror to focal point ○ Size of reflecting telescope refers to the diameter of its objective. ● The focusing of two beams of light by flat mirrors: other beams striking the mirrors won't be reflected to the same point ● A concave parabolic mirror: A concave mirror can bring all parallel beams that strike to a focus at the focal point ● All large modern astronomical telescopes are reflectors because it is difficult to make and to support large lenses in refracting telescopes. What are the various types of telescopes? How does a telescope work? What is the light-gathering power, resolution and magnification of a telescope? ● Types of telescopes ○ Optical and X-ray ■ Optical: Refracting, Reflecting, and Catodiotropic ■ X-ray: Uses cylindrical mirrors to focus light ● Light gathering power: the amount of light in can collect and focus ○ Area= pie x diameter ^2/4 = pie x radius ^2● Resolution: ability to distinguish fine details in an image and depends on the ratio of wavelength to the diameter of its objective ○ = 250000 x wavelength/diameter ● Magnification: diff to answer bc it can be changed by replacing eyepieces 2 How does the light gathering power of a 4 inch telescope compare to that of a 12 inch telescope? About 9 times Suppose a source of electromagnetic waves is moving away from us at 2% of the speed of light. What can be said of the wavelength of the waves we receive from the source? ● they are redshifted by 2% THE PRACTICE QUESTIONS AND ANSWERS: 1. You are located on the earth’s north pole the altitude of polaris is A. 0 degrees B. 90 degrees C. 180 degrees D. 30 degrees Why: Polaris’ altitude is always equal to the location’s latitude. 2. How many seconds are there in a degree? A. 120 B. 60 C. 600 D. 3600 Why: There are 60 minutes in a degree. A second of an arc is 1/60 of a min, So 60 x 60 is 3600. 3. During the night the stars generally move: ● Westward 4. The following coordinates describes the angular distance of an object from the celestial equator ● Declination Why: Declination: Equal to the angular distance of a star from the celestial equator 5. The declination of polaris is ● 90 degrees6. Night after night during a period of a year, a star has the same ● declination and right ascension Why: because the Vernal Equinox (position of the sun the first day of spring) moves with the stars, so RA and Dec remain the same throughout the night. 7. On the celestial sphere, the circle which is located 90 degrees from polaris is the A. Ecliptic (the path the sun follows among the stars) B. Meridian (Passes through the south pole, north pole and the zenith. The half of the circle above the horizon divides the sky into eastern and western halves.) C. Horizon D. Celestial equator Why:bc the equator is fixed between the 2 poles and polaris is also fixed??? 8. When there is a new moon the sun- earth - moon angle is A. 90 degrees B. 120 degrees C. 0 degrees D. 270 degrees Why: The moon is between the sun and Earth during a new moon therefore when drawing an angle between the three in the order Sun-Earth-Moon the angle would turn out to be 0 degrees. 9. The angular distance of an object from the horizon is its A. Declination (Equal to the angular distance of a star from the celestial equator) B. Altitude (The Angular distance above the celestial horizon and corresponds to the latitude in the terrestrial coordinate system) C. Latitude (Angle between the equator and a geographical location) D. Right ascension (Angular distance measured eastward along the celestial equator from the vernal equinox to the point on the celestial equator nearest the star’s position (measured in hours)) 10. What is the altitude of zenith ● 90 degrees 11. The width of an index finger held at arm's length fills an angle of about ● 1-2 degrees 12. In Tallahassee, which has 30 degrees latitude, the altitude of Polaris is ● 30 degrees Why: The personal latitude is about equal to Polaris’ altitude 13. The azimuth of an object located due south and on the horizon is ● 180 degrees Why: ● East= 90 degrees● South= 180 degrees ● West= 270 degrees ● North= 0 degrees or 360 degrees 14. The point directly over the observer's head is the ● zenith 15. The fist, held at arms length, fills about an angle of ● 10 degrees 16. On the celestial sphere, the circle which is located 90 degrees from the zenith is the ● Horizon Why: Because its the zenith, its the horizon. If it was polaris it would be the equator *I’m pretty sure this is because your zenith is in regards to your exact personal spot, therefore 90 degrees being the very bottom of your zenith would inherently be the horizon of wherever you’re standing. Horizon is also a term that varies dependent on where you are exactly at the moment. 17. The ecliptic is a great circle in the sky traveled by the sun in ● a year 18. Precession of the earth’s axis is the ● slow motion of the Earth’s rotation axis on the celestial sphere Why: Like a top, the Earth’s axis moves as well, just very gradually. It takes 26,000 years for the axis to make a full precession. 19. When there is full moon, the sun the earth and the moon form an ● 180 degree angle 20. Sometime ago the north celestial pole was going through Vega. How many earth years does it take the north celestial pole to start from Polaris and return to Polaris? ● 26,000 years. Why: It takes 26,000 years for the Earth to make a full precession, therefore for the axes to come full circle (literally) would take the full 26,000 years. 21. An object within an angular size of 1 degree moves two times farther away. What is its new angular size? ● 0.5 degree HOW ON EARTH ½ is .5 can i just divide the numbers 22. Imagine that we are ancients and we know that the earth is spherical because we have observed its shadow on the moon. In addition, we know that the earth rotates about its own axis because of the fact that we see day and night and the stars moving in circles around Polaris. After walking a distance of 100 km toward the north pole, we notice that the pole star is 1 degree higher in the sky. What is the circumference of our earth? >14,400km >10,000km >20,600km >36,000km 9,000kmx4=36,000km Why: 360 x 100 Those class quiz questions: 1. Most known contribution of Tycho Branhe to astronomy ● He had collected very accurate data 2. A hypothetical plaent orbits the sun at a dis of 3 AU. What is its orbital period? ● 5.2 SHOW ME THE MATH HELP :*( WHAT EQUATION? For some reason this was 3 squared is 9 times 3 is 27, square root of 27 is 5.2. Again. Don’t ask why. 3. When object A exerts a force on object B, then object B Didn't write down answer I answered (not positive if this is correct obvi) the force exerted is equal with respect to the masses of the objects. 4. What is law of inertia: An object remains at rest or continues in motion at constant velocity unless it is acted upon by an unbalanced external force 5. If the mass of sun was tripled, the force if gravity between the sun and the earth would Didnt write down answer and I have no clue I believe… triple. I believe. 1. Which of the following about wavelengths is true: As wavelength increases, frequency decreases 2. Compared with visible light waves, radio waves with wavelengths of one meter have A. Have higher energy B. Have higher frequency C. Are not composed of photons D. Longer wave units 3. Compare the light gathering power of a 3 in diameter lens with that of a 6 in diameter lens ● 6 dia lens is 4 times greater 4. We observe the wavelength of light from a moving source to be blue shifted by 3% relative to the wavelength emitted from the same source when it is not moving A. The light source moves away from us at 3% the speed of lightB. The light source moves toward us at 3% the speed of light C. Light Source moves away from us at 6% the speed of light D. Light source moves toward us at 6% the speed of light ● When an object moves away from us, the light is shifted to the red end of the spectrum, as its wavelengths get longer. If an object moves closer, the light moves to the blue end of the spectrum, as its wavelengths get shorter. ● Change in wavelength/original wavelength= speed approached/speed of light