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Why do seasons exist?
Earth’s axis tilt
How are seasons determined?
Position and axis tilt of Earth when orbiting the Sun
Four Special Points of Season Progression
Winter Solstice (December)
Spring Equinox (March)
Summer Solstice (June)
Fall Equinox (September)
Sun’s path during the Summer Solstice
Highest path; rise and sets at most extreme north due east
Sun’s path during the Winter Solstice
Lowest path; rise and sets at most extreme south due east
Sun’s path during equinoxes
Sun precisely rises due east and sets due west
How much sunlight does the Northern Hemisphere get during each solstice and equinox?
Summer Solstice: Most sunlight
Spring & Fall Equinox: Equal sunlight on both hemispheres
Winter Solstice: Least sunlight
Why do lunar phases occur?
Moon’s orbit around Earth
What is the moon illuminated by?
Half from the Sun and half is dark
How long is the moon phase cycle?
29.5 days
Phases of the Moon (Waxing)
New → Crescent → First Quarter → Gibbous → Full
Visible during afternoon/evening
Reveals itself more and rises later each day
Phases of the Moon (Waning)
Full → Gibbous → Third Quarter → Crescent
Visible during late night/morning
Starts disappearing and sets later each day
Lunar Eclipse
Earth’s shadow falls on the moon, giving it a reddish color
Can only occur during full moon
Can be Penumbral, Partial, or Total
Solar Eclipse
Moon’s shadow falls on the Earth
Can only occur during new moon
Can be Total, Partial, or Annular
Constellation
A region of the sky
How many constellations are there?
88 constellations
Celestial Sphere
A sphere where all the constellations lie at but at different distances
Ecliptic
Sun’s apparent path throughout the celestial sphere
Location of north and south celestial pole
North celestial pole: Above Earth’s North Pole
South celestial pole: Above Earth’s South Pole
The Milky Way
A wave of light circling the celestial sphere
How to know the location of an object in your local sky?
Its altitude and direction
Zenith
Directly above you(90 degrees)
Horizon
All points that are 90 degrees away from the zenith
Meridian
A line that passes through the Zenith and connects the North and South poles
Angular Measurements
Full Circle = 360 degrees
1 degree = 60’ arcminutes
1’ arcminute = 60” arcseconds
Visibility of Stars
Stars in the north celestial pole are circumpolar and never set
Cannot see stars in the south celestial pole
All other stars rise east and set west
Why do we see different constellations?
Position of Earth and the time of year
Ex: Sagittarius - Summer / Orion - Winter
(RAHHHHHH Beyblade taught me all these constellations)
What planets were known during ancient times?
Mercury - Most difficult to see, always near the sun in the SKY
Venus - Very bright when visible; morning/evening “star”
Mars - Noticeably red
Jupiter - Very bright
Saturn - Moderately Bright
Planetary Motion
When planets usually move a little eastward every night
Apparent Retrograde Motion
When the stars move westwards for a few weeks
Stellar Parallax
Using the Earth’s orbit(every 6 months) and distant “fixed” stars to determine the position of a nearby star
Ancient Greek’s conclusion on observable parallax
Earth does not orbit the sun; it is the center of the universe
Explanation: They didn’t think the stars could be THAT far away, meaning they tried using stellar parallax with the naked eye but couldn’t find any difference in star positions, hence the making of Earth-centered systems.
