Patterns in the Night Sky

The same lights are seen in the same positions in the sky night after night The whole sky does seem to drift slightly westward from one night to the next (at the same clock time, say 9:00, each night)

Patterns in those lights were given names - constellations There is nothing sacred about those images!

The Southern Hemisphere has some more modern-sounding constellations

Today, constellations are NOT patterns of stars They are well-defined regions of the sky (Defined by the IAU – International Astronomical Union)

An asterism is an easily recognized pattern of stars that is NOT a constellation

Which of the following is a constellation? A.The Summer Triangle B.The Big Dipper C.The Little Dipper D.The Air Pump E.The Plough

Stars and planets appear to ride on a sphere that surrounds the Earth. This celestial sphere is a model that is useful for thinking about how stars and planets move. It is NOT real!

These are the key components of the celestial sphere The Sun seems to move among the stars because of the Earth’s movement around the Sun (revolution) So ecliptic has two meanings

Earth’s orbit around the Sun causes to Sun to appear in front of different stars every day Ecliptic means the plane of the Earth’s orbit AND the path of the Sun through the stars

Why does the Milky Way look like a glowing band in our sky?

We are inside the flat disk of the Milky Way. Most stars are too far to see individually, but they add to the overall glow.

Which statement is incorrect? A.The Earth’s orbit around the Sun defines the plane we call the ecliptic. B.The Milky Way encircles the Earth in a plane we call the ecliptic. C.Over the course of a year, the Sun appears to move through the stars along a path we call the ecliptic. D.Both definitions of ecliptic are defined by the relative motion of the Earth and Sun.

The Local Sky nadir An (azimuth)

Sizes and distances in the sky are measured as angles degrees arcminutes arcseconds

When you point straight up over your head, you are pointing at the … A.Zenith B.Meridian C.Nadir D.Horizon E.Altitude

Why do stars rise and set? The Earth rotates west-to-east That makes the stars appear to move from east-to-west A person at the north pole has a horizon that is parallel to the celestial equator, but …

Why do stars rise and set? … a person far away from the north pole has a horizon that is tilted relative to the celestial equator Now some of those circles the stars make go below and above the horizon Exceptions: Those that never rise Those that never set: circumpolar

Circumpolar stars

Latitude and longitudeA point on the surface of the Earth is specified by its latitude and longitude What is the latitude of: The southern tip of Greenland? Ecuador? The North Pole? What is the longitude of: The southern tip of Greenland? The Yucatan Peninsula? Prime meridian

Where is the north celestial pole for someone at the north pole?

Do any stars rise or set?

Move further south, and the north celestial pole moves toward the horizon Watch this…

Move further south, and the north celestial pole moves toward the horizon Your latitude is equal to the altitude of the north celestial pole

Where was this picture taken? A.North Pole B.South Pole C.Equator D.Not enough information