The Constellations Video

Light year – the distance light can travel in a year. Stars are not necessarily close to one another, they can be light years away from each other. Light travels at 300 000 km/s or 3.0X108 m/s so a light year is…..9.5 x 1012 km in one year! Remember it is a unit of distance not time.

Constellation a group of stars that seem to form a particular figure in the sky There are 88 official constellations They are mostly named after mythological characters (Greeks and Romans)

Asterisms smaller group of stars that form patterns within a constellation (ex: “Big Dipper”  Great Bear (Ursa Major))

Time for light to travel… Sun to Earth = 8.3 min Alpha Centauri (star) to Earth = 4.4 years. Nearest galaxy to Earth = 25 000 years. Across the Milky Way = 100 000 years. Andromeda Galaxy to Earth = 2.5 million years Therefore when we see the light from a distant galaxy it is like looking into the past because that light took so long to travel to earth.

Apparent magnitude: A star’s brightness is called its apparent magnitude Heptarchs (130 B.C.E) – developed the first scale of apparent magnitude (1 brightest to 6.5 faintest). Now the scale goes beyond 6 and into the minus range. Sirius is the brightest star in the night sky

Brightest star in the night sky is Sirius

Polaris and the Pointer Stars Polaris = North Star Star that is most used for orientation by many ancient civilizations in the N. Hemisphere. When you see Polaris, you are looking North. Pointer stars in the Big Dipper are used to locate Polaris. The Earth’s rotational axis points to Polaris, it appears to stay still in the night sky.

Northern sky seems to revolve around Polaris – time lapse photography

Viewing different constellations We see different constellations each night because: 1. Earth’s revolution around the Sun, you see different constellations at different times of year

2. Latitude (location above or below equator) Constellations will look different in Ottawa compared to Miami 3. Earths rotation Stars also appear to move through the night sky because of earth’s rotation. Time lapse video

Homework Read sections______ Questions Star Chart/Planisphere questions Which of the following constellations is NOT visible on May 15th at 9:00 pm? The best time for viewing a group of stars is when it is due south of the observer. On what date is the constellation Orion due south of the observer at 9:00 pm? At what time of day is Scorpius due south of the observer on May 15th? Name the constellation that is due south at 2 am on December 1st? To what constellation does the star Arcturus belong? On May 31st at 11 pm, if you looked due North, you could not see Pieces. If you continue to look at the sky at what time would Pisces become visible?