Astronomy Notes – Unit 3 – Stars and Constellations
REVIEW
Ø The Celestial Sphere is an imaginary sphere with the Earth at its center that helps us understand how stars move in our night sky. This model shows how:
o Stars rise in the East and set in the West, just like the Sun.
o The Pole Star (Also known as Polaris or the North Star) doesn’t move in the night sky
o All the other stars appear to rotate around it over the course of the night.
o This star doesn’t move because it is where the Earth’s axis points to.
o The Big Dipper and Cassiopeia are on opposite sides of Polaris and “point” to it.
Ø God made the stars in an amazing variety. Some ways we classify them by:
o Brightness scale called Magnitude (larger numbers mean dimmer)
o Color and temperature
o Size
o Distance (in light years)
Ø Stars are grouped together in shapes called constellations and asterisms.
Ø Other visible objects in the night sky include nebulas, clusters and galaxies.
Ø Viewing stars and constellations:
o Those near the Pole Star are visible all the time (circumpolar).
o Some are visible only during certain seasons of the year due to the rotation of the Earth around the Sun.
o Some are not ever visible to us (here in the Northern Hemisphere) because the Earth is in the way. They are only visible from the Southern Hemisphere.
Ø We can use a Planisphere to show us what stars and constellations are visible at any given date and time.
Ø Our solar system is a part of the Milky Way galaxy.
Ø We discussed some of the more common and easily visible of the official 88 constellations, with some of the myths and legends behind the image:
o Ursa Major – The Great Bear ○ Canis Major – the Great Dog
o Taurus – the Bull ○ Gemini – the Twins
o Leo – the Lion ○ Virgo – the Virgin
o Cygnus
– the Swan ○
o Cepheus – the King ○ Cassiopeia – the Queen
o Andromeda and Perseus ○ Pegasus – the Flying Horse
Ø The Brightest objects in the sky include (with their magnitude)
o Sun (-26) ○ Moon (-12)
o Venus, Jupiter, etc. (-4 to 0) ○ Sirius (-1.5)
o Arcturus, Vega, Rigel (about 0) ○ Betelgeuse (0.5)
o Deneb (1.25) ○ Polaris (2)
1) Circumpolar: Describes stars and constellations which rotate about the Pole Star. They never rise, never set and can be seen at any time of the year.
2) Horizon: Line where the sky seems to meet Earth.
3) Zenith: The point in the celestial sphere directly over the observer.
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5) Ecliptic: The apparent path of the Sun among the stars in the course of a year.
6) Magnitude: A scale to measure star brightness.
7) Light Year: The distance light travels in one Earth year. At 186,000 miles per second, this equals about 6,000,000,000,000 (6 trillion) miles.
8) Nebula: A vast cloud of dust and gas in space.
9) Constellation: A group of stars forming a shape. There are 88 grouping that are historical rather than scientific.
10) Asterism: A cluster of stars that is smaller than a constellation.
11) Supernova: A catastrophic explosion of a large star.
12) Galaxy: A cluster of stars, dust, and gas held together by gravity.
q Handout from H.A. Rey’s “The Stars”
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