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Chapter Two Notes

by: Glaiza Julian

Chapter Two Notes 18762

Marketplace > Physics 2 > 18762 > Chapter Two Notes
Glaiza Julian
Cal State Fullerton
Astronomy 101
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Astronomy 101
No professor available
One Day of Notes
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This 10 page One Day of Notes was uploaded by Glaiza Julian on Friday September 19, 2014. The One Day of Notes belongs to 18762 at a university taught by a professor in Fall. Since its upload, it has received 232 views.


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Date Created: 09/19/14
Chapter 2 Discovering the Universe for Yourself 21 Patterns in the Night Sky What does the universe look like om Earth Constellations Constellation A region of the sky 88 official constellations cover the celestial sphere Constellations are a region of the sky with welldefined borders and the familiar patterns of stars merely help us locate these constellations Just as every piece of land in the US belongs to a state every star belongs to some constellation The Celestial Sphere Celestial Sphere The imaginary sphere on which objects in the sky appear to reside when observed from Earth We identify four special points and circles on the celestial sphere 1 North Celestial Pole The point on the celestial sphere directly above Earth s North Pole 2 South Celestial Pole The point on the celestial sphere directly above Earth s South Pole 3 Celestial Equator The extension of Earth s equator onto the celestial sphere 4 Ecliptic The Sun s apparent annual path among the constellations The Milky Way The band of light we call the Milky Way traces our galaXy s disk of stars the galactic plane as it appears from our location within the galaxy refer to page 27 Figure 25 l quotquote3939 91 2 3939rIk rm 2quot 39 39f 139aquot4I39r39 po39me quotw 3939399 rr3939L393939 M J390 J sled cw to the dvsmrr u39o vc39so Galactic plane When we 39looi 1 any dvnc39on We the g3a39c 3v39mc 39n 3939e rr39rwsvre see the Location 01 our stars 939r39 39n i739lt it39v39ar rv3939r3939ri that solar system 3939vM399 mu the Miquott39y 39391quotL39 39 the 3939r1quotn 1 The Milky Way appears much Wider towards the direction of the constellation Sagittarius that is the direction We are looking towards the galaXy s central bulge Dark lanes that run down the center of the Milky Way contain the densest clouds distorting our view of the stars behind them Only with advanced technology have we been able to peer through clouds by observing forms of light that are invisible to our eyes The Local Sky Local Sky The sky as viewed from a particular location on Earth or another solid object Objects in the local sky are pinpointed by the coordinates of altitude and direction or azimuth The dome shape arises from the fact that we only see half of the celestial sphere at any particular location Horizon A boundary that divides what we can see from what we can t see the boundary between Earth and sky Z The point directly ahead which has an altitude of 90 Meridian A halfcircle extending from your horizon altitude 0 due south through your zenith to your horizon due north Direction azimuth One of the two coordinates the other is altitude needed to pinpoint an object in the local sky It is the direction such as north south east or west in which you must face to see the object Altitude The angular distance between the horizon and an object in the sky 7e h ialttude 90 altitude 60 direction SE h0t i70r alt tudc I jjjjjjjjj 7 FIGURE 26 From any place on Earth the local sky looks like a dome hemisphere This diagram shows key reference points in the local sky It also shows how we can describe any positron in the local sky by Its altitude and direction Angular Sizes and Distances Angular Size A measure of the angle formed by extending imaginary lines outward from our eyes to span an object or the space between two objects Angular size alone does not tell us an object s true size because you must also take into account distance when pertaining to angular size Arcminutes 160 of 1 Arcseconds 13600 of 1 Calculating angular size physical size or distance Angular Size 360 Physical Size 21t gtlt distance Why do stars rise and set Circumpolar Star A star that remains perpetually above the horizon circling counterclockwise around the north celestial pole everyday Stars near the SCP never rise above the horizon Other stars have daily circles that are partly above the horizon and partly below which means they appear to rise in the east and set in the west Why do the constellations we see depend on latitude and time of year Variation with Latitude Prime Meridian The meridian of longitude that passes through Greenwich England de ned to be longitude 0 The constellations you see depend on your latitude but not your longitude The altitude of the celestial pole in your sky is equal to your latitude Variation with Time of Year Zodiac The constellations on the celestial sphere through which the ecliptic passes Tradition has 12 constellations along the zodiac but official borders also include a thirteenth constellation called Ophiuchus Whichever zodiac it is at the time you will be unable to see the constellation at night because the sun will be blocking your view 22 The reason for Seasons What causes the seasons Seasons occur because of the tilt of the Earth s axis that causes sunlight to fall differently on Earth at different times of year Refer to figure 215 Earth is only about 3 father from the Sun at its farthest point than at its nearest Solstices and Equinoxes There are four special moments in the year seasonally 1 June Solstice summer solstice which occurs around June 21 and is the moment where the Northern Hemisphere is tipped most directly toward the sun and receives the most direct sunlight 2 December Solstice winter solstice which occurs around December 21 and is the moment when the Northern Hemisphere receives the least direct sunlight 3 March Equinox spring equinox which occurs around March 21 and is the moment when the Northern Hemisphere goes from being tipped slightly away from the Sun to being tipped slightly toward the Sun September Equinox fall equinox or autumnal equinox which occurs around September 22 and is the moment when the Northern Hemisphere first starts to be tipped away from the Sun The Sun rises precisely due east and sets precisely due west only on the days of the March and September equinoxes Refer to bottom of page 36 for further elaboration on each of the seasonal days First Days of Seasons Why we consider the solstice to be the beginning rather than the midpoint of summer 1 Easier for ancient people to identify the days on which the Sun reached extreme positions in the sky rather than other days in between Typically we see seasons in terms of weather and the warmest summer weather comes 1 to 2 months after the solstice lnsert boiling soup analogy It takes some time for sunlight to heat the ground and oceans from the cold of winter to warmth of summer Seasons Around the World High latitudes have more extreme seasons Equatorial regions generally have rainy and dry seasons with the rainy seasons coming when the Sun is higher in the sky How does the orientation of Earth s axis change with time Precession The gradual wobble of the axis of a rotating object around a Vertical line The tilt of Earth s axis remains close to 23 but the direction the axis points in space changes slowly with the 26000year cycle of precession Precession is caused by graVity s effect on a tilted rotating object 23 The Moon Our Constant Companion Why do we see phases of the moon Lunar Phases the time period in which the moon s appearance in our sky changes as its position relative to the Sun changes The 29 day period is also the origin of the word month think month Understanding Phases Sunlight comes at both Earth and the Moon from the same direction Moon phases affects not only its appearance but also its rise and set times Refer to Figure 221 for illustrated moon phases The Moon s Synchronous Rotation We see many phases of the moon but not many faces We always see nearly the same face of the Moon Synchronous Rotation The rotation of an object that always shows the same face to an object that it is orbiting because its rotation period and orbital period are equal What causes eclipses Eclipses An event in which one astronomical object casts a shadow on another or crosses our line of sight to the other object Lunar Eclipse An event that occurs when the Moon passes through Earth s shadow which can occur only at full moon A lunar eclipse may be total partial or penumbral Solar Eclipse Occurs when the moon lies directly between the Sun and Earth so the Moon s shadow falls on Earth Conditions for Eclipses The moon s orbit is slightly inclined by about 5 to the ecliptic plane the plane of Earth s orbit around the Sun WimThe two points in the Moon s orbit where it crosses the ecliptic plane Umbra The dark central region of a shadow Penumbra The lighter outlying regions of a shadow Refer to Figure 225 page 44 to see the three types of lunar eclipses Lunar Eclipses Total Lunar Eclipse A lunar eclipse in which the Moon becomes fully covered by Earth s umbra shadow Partial Lunar Eclipse A lunar eclipse during which the Moon becomes only partially covered by Earth s umbral shadow Penumbral Lunar Eclipse A lunar eclipse during which the Moon passes only within Earth s penumbral shadow and does not fall within the umbra Penumbral eclipses are the most common but are the least Visually impressive because the full moon only darkens slightly Totality The portion of a total lunar eclipse during which the Moon is fully within Earth s umbral shadow or a total solar eclipse during which the Sun s disk is fully blocked by the 1 1 1001 1 Solar Eclipses Total Solar Eclipse A solar eclipse during which the Sun becomes fully blocked by the disk of the Moon Annular Eclipse A solar eclipse during which the Moon is directly in front of the Sun but its angular size is not large enough to fully block the Sun thus a ring or annulus of sunlight is still Visible around the moon s disk Partial Solar Eclipse A solar eclipse during which the Sun becomes only partially blocked by the disk of the Moon A total solar eclipse is Visible only within the narrow path that the moon s umbral shadow makes across the Earth s surface Predicting Eclipses Saros Cycle The period over which the basic pattem of eclipses repeats which is about 18 years 11 days The general pattem of eclipses repeats with the roughly 18 year saros cycle 24 The Ancient Mystery of the Planets Why was planetary motion so hard to explain Apparent Retrograde Motion The apparent motion of a planet as Viewed from Earth during the period of a few weeks or months when it moves westward relative to the stars in our Sky A planet appears to move backward relative to the stars during the period when Earth passes it in its orbit Why did the ancient Greeks reject the real explanation for planetary motion Stellar Parallax The apparent shift in the position of a nearby star relative to distant objects that occurs as we view the star from different positions in Earth s orbit of the Sun each year The Greeks knew that stellar parallax should occur if Earth orbits the Sun but they could not detect it


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