Constellations celebrating gods and hero’s by naming star groups.
Bright stars, light ones were not really included
Names are from Arabic, latin and greek
*Asterisms number of less formally defined groupings (big dipper)
Stars aren’t always in the same location or direction, they move.
Alpha brightest star, beta second brightest star
Magnitude Scale measure brightness of stars /6 brightness groups
Larger the magnitude number, fainter the star (scale moves downward so
brightest star has magnitude of 1)
Apparent visual magnitude how the stars look to us (humans) observing from
Flux (to be scientifically accurate) measure of the light energy from a star that
hits one square meter in one second
(ex. Say magnitude is 3.34 rather than a star is about third magnitude)
Some stars can have he magnitude scale that extends into negative numbers,
like Sirus(brightest star) has magnitude of 1.47.
Can extend numbers larger than 6 magnitude to include faint stars
Some stars emit large amounts of infrared or ultraviolet light (invisible to
Doesn’t tell us how bright the star actually is, only how it’s seen from the
Celestial Sphere (scientific model) –imaginary spheres of earth at its center on which
stars, sun moon seem to be attached.
*Not true because we know stars are scattered through space in various distances
Scientific model doesn’t have to be true to be useful (like chemists using atoms in
molecules to visualize them as spheres joined together by sticks) just helps us get a better
understanding of it. *
1. Sky rotates westward around the earth each day, consequence of eastward rotation
of the earth
2. What you see of the sky depends on where you are on earth
3. Measure distances across sky as angles expressed in units of degrees and
subdivision of degrees called arc minutes and arc seconds.
Precession Slow change in orientation of earth’s axis of rotation.
Earth spins like a giant top, not upright around the sun.
Earth’s large mass and rapid rotation keep its axis of rotation pointed toward a spot near
the star Polaris
Earth has a bulge in the middle, gravity of the sun and moon both pull on it, twisting
Earth’s axis upright. * LOOK INTO THIS.. confusing
Rotation turning of a body on its axis *earth rotating on its axis producing day and night Revolution motion of a body around a point outside the body. *Earth revolving around
the sun producing yearly cycle.
*Earth’s orbit is almost a perfect circle, not elliptical.
*Stars also appear during the day but sunlight fills our atmosphere with light.
*Every month, different sets of stars are projected (Libra October, AriesMarch)
*Sun moves eastward among stars following a line called the ecliptic (path of sun among
the stars), sun goes around he sky in the same period earth circles sun in 365.26 days.
o Revolution of earth around the sun and earth’s equator being tipped 23.5 degrees
o Seasons are NOT caused by distance between earth and sun, earth’s orbit is nearly
circular so always about the same distance from sun
o Seasons ARE caused by changes in amount of solar energy Earth’s northern and
southern hemispheres receive at different times of the ear.
o Signs of zodiac no longer important in astronomy
o Venus and Mercury orbit inside Earth’s orbit, never get far from sun and are
visible after a sunset, and before a sunrise… Venus can be really bright (4.7).
Motion of the Moon
Moves rapidly among the constellations. (slightly moves eastward if you watch it). Each
night it will be roughly half the width