Units of the Introduction The “Obvious” View Earth’s Orbital Motion The Motion of the Moon The Measurement of Distance Scientific Theory and the Scientific Method
What is Astronomy and how do we use the celestial sphere to study space?
What is Astronomy? Astronomy: study of the universe Universe Totality of all space, time, matter and energy Solar system, stars, galaxies, astrobiology, etc Actual science (physical) observations, data, facts
What is Astronomy? Astrology: study of the movements and relative positions of celestial bodies and their supposed influence on human affairs horoscopes, lunatics….
E.1 The “Obvious” View Earth is average – we don’t occupy any special place in the universe Scales are very large: measure in light-years, the distance light travels in a year – about 10 trillion miles THE BIGGEST STARS IN THE UNIVERSE VIDEO
Celestial Sphere Ancients used to think stars moved around Earth Stars’ apparent motion is due to Earth’s rotation on axis Axis intersection points: -North Celestial Pole -South Celestial Pole -Midway = Celestial Equator
Celestial Sphere -Stars seem to be on the inner surface of a sphere surrounding the Earth -They aren’t!! -Use two-dimensional spherical coordinates (similar to latitude and longitude) to locate sky objects
E.1 Celestial Coordinates Declination: degrees north or south of celestial equator (similar to latitude) Celestial Equator = 0° (0-90) Above CE = +X°; below CE = -X°
E.1 Celestial Coordinates Right ascension (RA): measured in hours, minutes, and seconds eastward from position of Sun at vernal equinox (similar to longitude; east-west)
E.1 Celestial Coordinates Right ascension: Starting Line (0) = line from North star to Sun on the vernal equinox (March 21) Maximum RA= 24 hrs
How does the Earth’s orbital motion cause changes on Earth?
Revolution vs. Rotation Revolution: time it takes to orbit around an object EXAMPLE Earth year: 365 ¼ days around the sun (counterclockwise) Moon: ~27 1/3 days around Earth (cc)
Revolution vs. Rotation Rotation: time it takes to complete a turn on its own axis EXAMPLE Earth day: 24 hours (counterclockwise) Moon: ~27 1/3 days (cc)
Synchronous Rotation Rotation time = Revolution time Always see same side of the moon!
E.2 Earth’s Orbital Motion Solar day- Daily cycle, noon to noon, is diurnal motion 24 hours Sidereal day – Time it takes the stars to be in the exact same location 23 hrs 56 min “sidus”= star
E.2 Earth’s Orbital Motion Ecliptic is plane of Earth’s path around Sun at 23.5° to celestial equator
E.2 Earth’s Orbital Motion Northernmost point (above celestial equator) is summer solstice Southernmost is winter solstice Points where path cross celestial equator are vernal and autumnal equinoxes
E.2 Earth’s Orbital Motion
Summer solstice longest amount of daylight of year usually June 21 first day of summer Winter solstice shortest amount of daylight of year usually Dec. 21 or 22 first day of winter
E.2 Earth’s Orbital Motion Vernal equinox equal amount of daylight and dark usually March 20 or 21 first day of spring Autumnal equinox equal amount of daylight and dark usually Sept first day of fall
E.2 Earth’s Orbital Motion Seasons are caused by: Combination of day length and sunlight angle due to axis TILT Not distance from sun Perihelion- January 3 Aphelion- July 4
E.2 Earth’s Orbital Motion Tropical year (Our calendar) Time from one vernal equinox to the next Follows seasons Sidereal year Time for Earth to orbit once around Sun, relative to fixed stars Follows constellations In 13,000 years July and August will still be summer, but Orion will be a summer constellation
Watch the changing seasons l Notice it is harder to tell in Southern Hemi. Because not as much land
E.2 Earth’s Orbital Motion Precession: rotation of Earth’s axis itself; makes one complete circle in about 26,000 years (like a top)
Essential Question How does the motion of the moon cause us to see different phases and different types of eclipses? animated GIF created by Antonio Cidadao
E.3 Motion of the Moon Half of moon’s surface is ALWAYS illuminated by the sun!!! Wax-grow Right edge Wane-shrink Left edge
Motion of the Moon Lunar Phases animated GIF created by Antonio Cidadao
E.3 Motion of the Moon Synodic month 29.5 days to go through whole cycle of phases Phases -different amounts of sunlit portion being visible from Earth Sidereal month Time to make full 360° around Earth (orbital time) 27.3 days
Moon Features Natural Satellite Gravity causes tides Maria Most obvious darkened areas Craters Circular, bowl shaped holes Formed by impacts long ago No erosion forces Atmosphere, water, wind
Motion of the Moon Eclipse: When the sun or moon is blocked to an observer on Earth for a short period of time (minutes or hours) Caused by shadows of Earth or Moon Umbra- darkest part of the shadow Penumbra- lightest part of the shadow Lunar eclipse: Moon is blocked Solar eclipse: Sun is blocked
Motion of the Moon Lunar eclipse: Earth is between Moon and Sun Only occurs during full moon phase
When the Earth’s shadow covers the Moon, we have a lunar eclipse
3 types of Lunar Eclipses 1.Penumbral 2.Partial 3.Total
3 types of Lunar Eclipses Penumbral lunar eclipse the Moon only passes through the penumbra of Earth’s shadow
3 types of Lunar Eclipses Partial lunar eclipse part of the Moon passes through the umbra of Earth’s shadow
3 types of Lunar Eclipses Total lunar eclipse the entire Moon passes through the umbra of Earth’s shadow (turns red) Total Lunar Eclipes Time Lapse Video *Next Total Lunar Eclipse not until April 15, 2014*
Why is the Moon red during an eclipse? Atmosphere filters some sunlight and allows it to reach the Moon’s surface Atmosphere filters some sunlight and allows it to reach the Moon’s surface Blue light is removed Blue light is removed Remaining light is red or orange Remaining light is red or orange Bent or refracted so that a small fraction of it reaches the Moon Bent or refracted so that a small fraction of it reaches the Moon Exact appearance depends on dust and clouds in the Earth’s atmosphere Exact appearance depends on dust and clouds in the Earth’s atmosphere
E.3 Motion of the Moon Solar eclipse: Moon is between Earth and Sun New Moon 3 types 1.Partial 2.Total 3.Annular
E.3 Motion of the Moon Partial part of Sun is blocked Seen by people located in the penumbral shadow
E.3 Motion of the Moon Total entire sun is blocked Corona becomes visible Low density cloud of plasma with higher transparency than the inner layers “Diamond Ring” effect
“Diamond Ring” Effect Before Totality Begins In the last seconds before totality begins, the remaining bit of Sun resembles a dazzling jewel as the ring-like corona appears.
Photo of a Total Solar Eclipse
Total Solar Eclipse from Antarctica It’s possible to see a total eclipse from anywhere on Earth. This image was shot in Antarctica in Credit: Fred Bruenjes
E.3 Motion of the Moon Annular- Moon is too far from Earth for total (umbra doesn’t reach surface of Earth) Forms a ring No corona visible photos taken by Fred Espenak
Annular Solar Eclipse
Solar Eclipse This is a photo taken from the former Soviet space station MIR. It shows the shadow of the Moon falling on the Earth in Anyone under the shadow saw a solar eclipse.
E.3 Motion of the Moon Eclipses don’t occur every month because Earth’s and Moon’s orbits are not in the same plane 5° tilt compared to ecliptic
E.3 Motion of the Moon Eclipse tracks,
Constellations and parallax How do astronomers identify stars, name stars and calculate their distances?
Constellations Patterns of stars in the sky that’s “relative” distance doesn’t change Most visible in Northern Hemisphere named after mythological heroes and animals by Greek astrologers Different constellations visible at night during different times of year; appear to move from east to west during night 88 total constellations Still used to specify large areas of the sky
Locating a star Easiest way: specify constellation then rank in order of brightness using Greek alphabet Alpha (α)- Brightest star Beta (β)- Second brightest Method can only be used with naked eye since limited number of letters
The “Obvious” View Stars that appear close in the sky may not actually be close in space:
Earth’s Orbital Motion 12 constellations Sun moves through during the year are called the zodiac
The Measurement of Distance Triangulation: measure baseline and angles, can calculate distance
The Measurement of Distance
Parallax: similar to triangulation, but look at apparent motion of object against distant background from two vantage points Larger parallax= closer the object Smaller parallax= farther the object
Measuring with Parallax 1.Ruler, tape, cardboard, scissors 2.Cut out both pieces along dashed line 3.Fold up arrows on dotted lines 4.Stick pushpin through both pieces and cardboard 5.Select a colored target 6.Make a perpendicular baseline taping ruler to desk
Measuring with Parallax 1.Put EYE ARROW on one end of baseline 2.Line up EYE ARROW, REFERENCE ARROW and REFERENCE POINT (corner)-gunsight 3.Pivot TARGET ARROW until it is aligned with EYE ARROW and TARGET OBJECT (scale piece should NOT move, only the pointer) 4.Read “Angle to Target object” and put on worksheet as “Target Angle 1” 5.Repeat previous steps from opposite side of the baseline and write down Angle in “Target angle 2” 6.Complete calculations (Baseline=30 cm)
Scientific Theory and the Scientific Method What is a Scientific theory and how is it developed?
Scientific Theory and the Scientific Method Scientific theories: must be testable must be continually tested should be simple should be elegant Scientific theories can be proven wrong, but they can never be proven right with 100% certainty
Scientific Theory and the Scientific Methods Observation leads to theory explaining it Theory leads to predictions consistent with previous observations Predictions of new phenomena are observed. If the observations agree with the prediction, more predictions can be made. If not, a new theory can be made.
Summary of the Introduction Astronomy: study of the universe Stars can be imagined to be on inside of celestial sphere; useful for describing location Plane of Earth’s orbit around Sun is ecliptic; at 23.5° to celestial equator Angle of Earth’s axis causes seasons Moon shines by reflected light, has phases Solar day ≠ sidereal day, due to Earth’s rotation around Sun
Summary of the Introduction Synodic month ≠ sidereal month, also due to Earth’s rotation around Sun Tropical year ≠ sidereal year, due to precession of Earth’s axis Distances can be measured through triangulation and parallax Eclipses of Sun and Moon occur due to alignment; only occur occasionally as orbits are not in same plane Scientific method: observation, theory, prediction, observation, …