'Cold hearted orb that rules the night, Removes the colours from our sight. Red is grey and yellow white, But we decide which is right. And which is an illusion? Pinprick holes in a colourless sky, Let inspired figures of light pass by The mighty light of ten thousand suns, Challenges infinity and is soon gone. Night time, to some a brief interlude, To others fear of solitude. Brave Helios wake up your steeds, Bring the warmth the countryside needs. The Moody Blues, Days of Future Passed

Assignment: Reading: Explorations, pp. 28-34 Sign up for a time slot for Observing Lab #1. Problem Set #1 is due Thursday, 1 September.

In Class: Question to Ponder Early in the evening during this time of year, you can catch the teapot-shaped constellation of Sagittarius low in the southern sky. If you were to travel south to Key West, Florida, this constellation would appear a) higher in the sky. b) lower in the sky. c) at the same altitude. d) shaped like a conch shell. A Graphical Approach to Determining a Star's Altitude Cutaway Earth Diagram Lines from the center of the Earth to the surface define the vertical direction at each point. Horizons at each point are perpendicular to the local vertical. Since both observers are looking at the same star, the black arrows are parallel. However, the horizons have shifted, and the altitude of the star at Key West is larger (or higher). The Rotation of the Sky Caused by our rotation One point appears not to move at all -- North Celestial Pole (NCP) All other objects appear to rotate around NCP in circles Finding the Altitude of the NCP Another Cutaway Earth Diagram Lines from the center of the Earth to the surface (red for Lewisburg, black for Equator and North Pole) define the vertical direction. The horizon (green) is perpendicular to the local vertical. Direction to NCP (black arrow) is parallel to vertical at the North Pole (NP). Angles labeled B are the same because they're made by the red line crossing the two parallel black lines. Angles labeled A are the same because both are complements of B (i.e., A + B = 90 degrees at both locations). A is both the altitude of the NCP and the latitude of your location.