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Another Complication: Axis Tilt!. The Earth’s rotation axis is tilted 23½ degrees with respect to the plane of its orbit around the sun (the ecliptic ) It is fixed in space sometimes we look “down” onto the ecliptic , sometimes “up” to it . Rotation axis. Path around sun.
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Another Complication: Axis Tilt! • The Earth’s rotation axis is tilted 23½ degrees with respect to the plane of its orbit around the sun (the ecliptic) • It is fixed in space sometimes we look “down” onto the ecliptic, sometimes “up” to it Rotation axis Path around sun
Activity: The Ecliptic Get out your activities book Form a group of 3-4 people Work on the questions Hand in a sheet of paper with the title of the activity and the names of the group members I’ll come around to help out !
The Seasons • Change of seasons is a result of the tilt of the Earth’s rotation axis with respect to the plane of the ecliptic • Sun, moon, planets run along the ecliptic
Position of Ecliptic on the Celestial Sphere • Earth axis is tilted w.r.t. ecliptic by 23 ½ degrees • Equivalent: ecliptic is tilted by 23 ½ degrees w.r.t. equator! • Sun appears to be sometime above (e.g. summer solstice), sometimes below, and sometimes on the celestial equator
Zodiacal signs vs. Constellations • “Constellation” is a modern, well-defined term • - Some constellations are big, some are small on the celestial sphere • “Zodiacal sign” is the old way of dividing the year and the Sun’s path into 12 equal parts • 360/12=30, so each zodiacal sign is exactly 30 degrees “long” • 0 degrees: Aries, 30 degrees: Taurus, 60 degrees: Gemini, 90 degrees: Cancer, etc.
Constellation Quiz Workshop Learn the data on the Constellation Quiz Data Sheet: - constellation shapes and names - star names and position in constellation - deep sky objects’ names and position Quiz: You will be asked to find these objects on a star map.
Constellations of Stars About 5000 stars visible with naked eye About 3500 of them from the northern hemisphere Stars that appear to be close are grouped together into constellations since antiquity Officially 88 constellations (with strict boundaries for classification of objects) Names range from mythological (Perseus, Cassiopeia) to technical (Air Pump, Compass)
Constellation 1: Orion Orion as seen at night Orion as imagined by men
Orion “from the side” Stars in a constellation are not connected in any real way; they aren’t even close together!
Constellation 1: Orion “the Hunter” Bright Stars: D) Betelgeuze E) Rigel Deep Sky Object: i) Orion Nebula
Constellation 2: Gemini “the Twins” zodiacal sign Brightest Stars: I) Castor J=K) Pollux
Constellation 3: Taurus “the Bull” zodiacal sign Brightest Star: F) Aldebaran Deep Sky Object: iii) Plejades
Constellation 4: Ursa Major Other name: Big Dipper Stars: B) Dubhe C) Merak Navigation: go 5 times the distance from Merak to Dubhe and you are at Polaris.
Constellation 5: Ursa Minor Other name: LittleDipper α Ursa Minoris is Polaris [A], the pole star
Constellation 6: Canis Major “Big Dog” Stars: H) Sirius (brightest fixed star)
Constellation 7: Cancer “Crab” No bright Stars
Constellation 8: Leo “the Lion” zodiacal sign Brightest Star: G) Regulus
Constellation 9: Cassiopeia Greek mythological figure: mother of Andromeda the big “W” in the sky No bright stars
Constellation 10: Pisces “the Fishes” Zodiacal sign No bright stars
Constellation 11: Pegasus Greek mythological figure: the winged horse big rectangle in the sky No bright stars
Constellation 12: Andromeda Greek mythological figure: Daughter of Queen Cassiopeia and King Cepheus rescued from Cetus by Perseus Deep Sky Object: Andromeda Galaxy
