axis
the imaginary line that cuts through the Earth from the North Pole through the center of the Earth and out the South Pole; tilted 23.5 degrees toward the North Star (Polaris)
rotation
the spinning of Earth on its axis; causes day and night
revolution
the movement of one object around another
calendar
a system of organizing time that defines the beginning, length, and divisions of a year
ellipse
oval shape; shape of the planetary orbits
oblate spheroid
shape of our planet; flatter at the poles and bulging at the equator
equinox
equal night"; sun is directly above the equator; vernal (spring) equinox occurs around March 21; Autumnal (fall) equinox occurs around September 22; approximately 12 hours of daylight world-wide
solstice
the sun is at its northern most or southern most point from the equator; summer solstice is longest day of the year and occurs around June 21; winter solstice is the shortest day of the year and occurs around December 21.
lunar phases
the different shapes of the moon seen from Earth
solar eclipse
occurs when the moon passes directly between the Earth and sun, blocking sunlight from Earth; occurs during the new moon phase
lunar eclipse
occurs when the Earth is directly between the sun and the moon blocking sunlight from the moon; occurs during the full moon phase
umbra
darkest part of the shadow cast by an object
penumbra
largest part of the shadow cast by an object; it is less dark than the umbra
tides
caused mainly by differences in how much gravity from the moon and the sun pulls on different parts of Earth
spring tide
both the sun and the moon are pulling on Earth; sun-moon-earth line up; greatest difference between the high and low tides; occurs during a full or new moon
neap tide
the sun-moon-earth are lined up at right angles; least difference between high and low tides; occurs during a first or last quarter moon
geocentric
earth is at the center of the revolving planets and sun
heliocentric
sun is at the center of the revolving planets; Earth and all planets revolve around the sun
astronomical unit
equals the average difference between the Earth and the sun
solar system
consists of the sun, the planets, their moons, and a variety of smaller objects including meteoroids, asteroids, and comets
planet
must be round; orbit the sun;and have cleared out the region of the solar system along its orbit
dwarf planet
an object that orbits the sun and has enough gravity to be spherical but has not cleared the area of its orbit
inner planets
also known as terrestrial or rocky planets; include Mercury, Venus, Earth and Mars
outer planets
also known as gas giants or Jovian planets; include Jupiter, Saturn, Uranus and Neptune
greenhouse effect
the trapping of heat by the atmosphere
asteroid belt
region of the solar system between Mars and Jupiter
Kuiper belt
begins beyond Neptune's orbit and extends to about 100 x Earth's distance from the sun
Oort Cloud
located beyond the Kuiper belt; a spherical region of comets; stretches out more than 1000 x the distance between the sun and Neptune
comets
loose collections of ice, dust and small rocky particles whose orbits can be very long; "dirty snowball"; has a head (with a nucleus and coma) and a tail
asteroid
rocky objects too small to be considered dwarf planets
meteoroid
chunks of rock or metal that are too small to be considered asteroids
waxing
to increase in size
waning
to decrease in size
eclipse
when an object in space comes between the sun and a third object, it casts a shadow on that object
nuclear fusion
the process by which hydrogen atoms join to form helium atoms; requires extremely high temperatures and pressure
core (sun)
central region where the sun produces an enormous amount of energy through nuclear fusion
prominence
huge, looping eruptions of gas, usually near sunspot regions, that arch out from the photosphere into the corona
sun spot
areas of gas on the Sun that are cooler than surrounding gasses and do not give off as much light--appear as dark spots on the photosphere
solar flare
eruptions of hot gas that occur near sunspot regions-they shoot out from the Sun's surface releasing tremendous amounts of energy into space
solar wind
streams of electrically charged particles
corona
outermost layer of the Sun's atmosphere that extends outward several million km--looks like a halo--only seen during total solar eclipse
photosphere
surface of the Sun "sphere of light
chromosphere
middle layer of the Sun's atmosphere that has a pinkish color that is visible during a total solar eclipse "sphere of color