Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Cycles of the Sky
Transcript
2/4/12 THE CELESTIAL SPHERE • The view of space from Earth (gigantic dome) • Total view is blocked by horizon CHAPTER 1 • Stars are all at different distances CYCLES OF THE SKY • From space the view changes THE CELESTIAL SPHERE CONSTELLATIONS • Constellations are fixed arrangements of stars that resemble animals, objects, and mythological figures • Stars in a constellation are not physically related DIURNAL MOTION CONSTELLATIONS • • • • • • Positions of stars change very slowly; constellations will look the same for thousands of years • Origin of the ancient constellations is unknown although they probably served as mnemonic tools for tracking seasons and navigation • Daily motion (axis rotation) Sun, Moon, planets and stars rise in the east and set in the west Due to Earth’s rotation Rotation of the celestial sphere North and south celestial poles (directly above Earth’s north and south poles) • Polaris (north star) The celestial equator lies directly above the Earth’s equator 1 2/4/12 ANNULAR MOTION ANNUAL MOTION • “Yearly Motion” • Due to the Earth’s revolution • Revolution around Sun • Night sky changes season to season • Bright sun hides constellation each month For a given time (say 10:00 PM), as the months proceed, constellations do not appear in the same part of the sky THE ECLIPTIC ZODIAC • The path of the Sun through the stars on the celestial sphere is called the ecliptic • The ecliptic passes through 12 constellations • • • • • • • • • • • • • When a new or full moon crosses the ecliptic an eclipse occurs. THE SEASONS • The Earth is closest to the Sun in January • Winter in the northern hemisphere • The Earth’s rotation axis is tilted 23.5º Aries Taurus Gemini Cancer Leo Virgo Libra Scorpius Sagittarius Capricornus Aquarius Pisces THE SEASONS • The rotation axis remains same tilt and direction • December southern hemisphere gets direct sunlight • June northern hemisphere gets direct sunlight • This leads to the seasons! 2 2/4/12 THE SEASONS Bottom ray - Same amount of sunlight over a larger area Lower temperature - Winter SOLSTICES AND EQUINOXES THE ECLIPTIC’S TILT • Only 2 dates when sun crosses the celestial equator • March 21st and Sept 22nd SOLSTICES AND EQUINOXES When sun crosses celestial equator Equal day and night Equinoxes Sun rises due east and sets due west Positions of sun on horizon changes throughout the year March 21 and September 22 The day the sun is at it’s highest (lowest) point in the sky Solstice Longest (shortest) day of the year June 21 and December 21 THE MOON THE PHASES OF THE MOON Rises in the east and sets in the west Changes position and shape throughout the month Lunar phases (29.5 days) 3 2/4/12 THE PHASES OF THE MOON LUNAR RISE AND SET TIMES The Moon rises roughly 50 minutes later each day Because of the difference between earth’s rotation and the moon’s revolution • Moon shape changes because as it moves around Earth we are only able to see parts of the illuminated surface. • Full Moon • Sun à Earth à Moon • New Moon (can’t see it) • Sun à Moon à Earth ECLIPSES ECLIPSES Corona – outer atmosphere of the sun Prominence – tiny glowing red flame-like clouds in the sun’s atmosphere An eclipse occurs when the Sun, Earth, and Moon are directly in line with each other A solar eclipse occurs when the Moon passes between the Sun and Earth, with the Moon casting its shadow on the Earth SOLAR ECLIPSE FROM SPACE LUNAR ECLIPSES A lunar eclipse occurs when the Earth passes between the Sun and Moon, with the Earth casting its shadow on the Moon giving it a dull red color The Earth’s atmosphere bends light Blue light is removed Red like sunsets 4 2/4/12 RARITY OF ECLIPSES ECLIPSE SEASONS When conditions are right New Moon Solar Eclipse Full Moon Lunar Eclipse Generally occur in pairs 14 days apart Because of the Moon’s tilt relative to the ecliptic, eclipses will not occur at every new and full Moon Twice a year the Moon’s orbit will pass through the Sun giving the possibility of an eclipse – these times are called eclipse seasons ECLIPSE PERIODS RECENT AND UPCOMING SOLAR ECLIPSES Eclipses do not occur every 30 days since the Moon’s orbit is tipped relative to the Earth’s orbit The tipped orbit allows the shadow of the Earth (Moon) to miss the Moon (Earth) RECENT AND UPCOMING SOLAR ECLIPSES 5
