• Need to know - Astronomy

    -The geocentric theory says that the Earth is at the center of the solar system/ universe. This is obviously not true.
    -The Heliocentric theory makes the sun the center of attention rather than the earth. This correctly explains all movements that we see from Earth.
    Rotation- to spin around an axis.
    • How long does it take the Earth to spin once?
    • How many degrees is a full spin?

    360°÷24hours= 15°/hr
    Earth spins at 15 degrees per hr

    Revolution- to orbit around an object.
    • Earth travels about 1 degree per day around the Sun. A full trip takes 365 ¼ days.
    Earth is Tilted 23.5°  on it's Axis (the imaginary line that Earth rotates on.)
    The TILT, along with the revolution create our changing seasons.
    Name Date Key points

    Summer Solstice



    June 21

    North Pole is tilted towards the sun

    Sun is highest in the sky in NY

    Longest day, shortest night

    Sun is directly over the Tropic of Cancer.

    Fall (autumnal) Equinox

    September 23

    Equal day and night

    Sun is directly over the equator

    Winter Solstice

    December 21

    North Pole is tilted away from the sun

    Shortest day, longest night

    Sun is directly over the Tropic of Capricorn

    Spring (vernal) Equinox

    March 21

    Sun is directly over the Equator

    Equal day and night

    *Note: The seasons are NOT caused by the distance from the sun.

    The Sun travels on a different path at different times of the year. This diagram should help you understand:
    Sun Path
    Think of the length of the stick figure's shadow when the Sun is at different positions... when is the shadow longest? When is the shadow shortest?
    • In New York, the Sun never gets directly overhead. (You need to be within the Tropic of Cancer and Capricorn to experience that.)
    • In New York, at any time of the year, the noon time sun will always be in the southern half of the sky, causing the shadow of the tree/stick/observer to point towards the north.

    All planets travel in elliptical orbits with the sun at one focus.

    Note: The Earth's orbit is so close to a perfect circle that it can't be distinguished with the human eye.

    Here's a highly exagerated drawing of Earth's elliptical orbit: ellipseThe terms "aphelion" and "perihelion" in the picture above refer to Earth's shortest and longest distances to the Sun.

    -Planets that are closer to the Sun travel faster in their orbit.

    THE MOON: Earth's natural satellite.
    Waxing: More light is appearing ON THE RIGHT SIDE. "Wax on"
    Waning: More darkness is appearing ON THE RIGHT SIDE. "Wane, Wane, go away"
    Crescent: Less than half the Moon is lit up.
    Gibbous: More than half the Moon is lit up.
    Full: The side of the Moon facing the Earth is fully lit up.
    New: No moon is visible, the lit side is not facing Earth.
    1st Quarter: The moon is 1/4 of the way around it's orbit, the right half is lit up.
    3rd Quarter: The moon is 3/4 of the way around it's orbit, the left half is lit up.
    Whatever you see on the right side of the Moon with be "taking over." Example: A waxing crescent would be like the July 20th picture below. The next night, more light would be coming in from the right side, until the Moon appears Full. Then darkness begins to creep in. (Also from the right!)
    Lunar Eclipses occur when the Earth blocks out the Moon's sunlight. The moon "gets dark" as it goes into the Earth's shadow. Lunar eclipses can only happen during a Full Moon.


    A solar eclipse is when the Sun "gets dark" because the moon blocks sunlight from reaching the Earth. Solar Eclipses can only happen during a New Moon.

    TIDES: Caused by the line up of the Sun, Moon, and Earth. There are two different tides that result from the orientation of these three bodies.
    Spring Tide: caused by a full moon and a new moon. The water springs from its highest level to its lowest for the month.
    spring tide
    Neap Tide: happens during the 1st and 3rd quarter moons. High tide is not so high, and low tide is not so low.
    neap tides
    Due to Earth's rotation of 15 degrees per hour, stars will "leave a trail" 15 degrees long for every hour the shutter on a camera is left open. This is a star trail photo: Notice which star does not move very much... it is POLARIS! (center)
    star trails
    Stars that never go below the horizon are called circumpolar stars. These stars are visible all year. The big dipper is the most widely known circumpolar constellation.
    You have a bunch of info about stars in your ESRT that looks like THIS:
    hr diagram
    With stars, there is more to the eye than we can see, so we use special tools to observe light of different wavelengths. Your ESRT can help with that too.  Notice how small the "visible" portion of the spectrum is!

    When an element is heated, it gives off light. As seen through a prism, the light will split into the basic colors that make that light (just like the rainbow). Each element has its own unique light with its own pattern of colors sometimes called the fingerprint of an element.
    Who cares? Well... since we rely totally on sight, if we study these special basic color patterns, we can learn a lot about the universe.
    The most imporant thing is that we can tell if stars are moving. Here's how:
    When we look through a spectroscope, this is was hydrogen looks like when it is standing still:
    hydrogen still
    However, if hydrogen is moving away from us, it looks like the image below:
    hydrogen moving
    As you can see, the lines of color are "SHIFTED"      <--------------------------
    towards the RED side of the spectrum. We call this RED SHIFT and it is proof that the universe is expanding! Very cool.

    Since the universe is expanding...
    All distant objects have a red shift.

    The farther the object, the more extreme the red shift.
    Objects that show lines shifted towards the blue end of the spectrum are moving towards you.... RUN!
    We also use the Doppler Effect to explain movement. Think of the pitch of a siren on a cop car sounds when coming towards you. Think about how it changes as the car speeds past you and begins to move away from you. This image might help, you can see how the lines are "bunched" together as the sound is approaching, and more spaced out on the other side. Where the lines are bunched, we know the object is moving closer to us, and in this case, the pitch of the siren gets higher.
    Thats all the "BIG STUFF"
    Is your brain full yet?

Last Modified on October 11, 2011