ast3018lecture1 - Daily Motions Sun: Daily Motions S ta r s...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Daily Motions • Sun: – rises in the east – sets in the west – travels on an arc across the sky – 24 hours Solar Day = 24 hours Daily Motions • Stars: – stars travel on arcs in the sky moving from east to west. – some stars rise and set – others do not and are circumpolar – due to Rotation of Earth • 23 hour 56 min Sidereal Day = 23 hours 56 min Solar and Sidereal Days Why is the Solar Day longer than the Sidereal Day? Annual Motions of the Sun • The altitude of the Sun changes with season – It reaches a maximum on the summer solstice (June 21 in the northern hemisphere) – Its minimum altitude is reached on the winter solstice (December 21 in the northern hemisphere) • The sunrise and sunset points along the horizon also change with season – It rises and sets due east on the equinox (Sep 21, and March 21) – It rises north of east in the summer south of east in the winter Annual Motion of the Stars • Every day a given star or constellation rises and sets 4 minutes earlier with respect to the Sun • Therefore after one year it returns to the same position relative to the Sun Coordinate system on Earth Gainesville: 29.6510N, 82.3250W
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Celestial Sphere • You can imagine that the stars and sun are attached to the surface of a great sphere • The earth appears to be at the center of the sphere • The sphere rotates from east to west on an axis that points to the north celestial pole • To explain the daily motions of the sky you can imagine the sphere rotating once in 23 hours 56 minutes Parts of the Celestial Sphere • Celestial pole - extends from the rotation axis of the earth – all stars appear to rotate about this point – some stars are circumpolar
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 6

ast3018lecture1 - Daily Motions Sun: Daily Motions S ta r s...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online