Lecture 5 – The Night Sky What is the connection between what’s in the book and what’s in the sky?

We will discuss many types of objects; let’s see them too Examples: Red Supergiants (Antares) “Population II Stars” (Arcturus) Galaxies (M81) Basic astronomical phenomena known since antiquity First, we need a system to describe the sky

First reference system: the Horizon System Two coordinates: altitude and azimuth

In Horizon System, we see motions in the sky The Sun rises in the east, reaches highest altitude angle due south, sets in the west When the Sun sets, it gets dark and we see the stars and planets The Moon “ “ “ “ “ The Moon rises at a different time each night and is seen against a different constellation The constellations in the evening sky are different in different seasons

Question for the audience: What is going on to cause this east-to-west motion of all objects, rising in east and setting in west?

Seasonal differences in the night sky: go out tonight at 10PM Constellations Bootes almost overhead Constellation Leo in the west Bright star Vega low in the east Constellation of Virgo in the south Constellation of Scorpius (with bright star Antares) low in southeast. Check it out with the help of the SC1 chart!

Go out again at 10PM in mid- September Scorpius (and Antares) will be due south, to south-west The constellation Aquila (bright star Altair) will be in southeast Bright star Vega straight overhead Arcturus and Bootes way over in the west Come back in February, more changes still

Question: What causes this phenomenon of the “Parade of the Constellations”? Demonstration, more next time