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 Path around sun Rotation axis

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 -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” 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

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; t hey 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: Little Dipper 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