 The Night Sky Astronomy, the Earth and Constellations

Astronomy  Astronomy – is a branch of science that involves observations and explanations of events that occur beyond Earth and its atmosphere

Video’s  The Big Bang –  Mars Rover Curiosity –   First Moon Landing -

Earth’s Motion  Earth undergoes two important motions : Rotation and Revolution  Rotation – is the spinning of an object around an imaginary line called an axis.  Revolution – is the motion of an object around another object.

Rotation and Revolution  The effect of rotation is how we have a 24 hour day.  The earth spins counter-clockwise; this is why the sun rises in the east and sets in the west.  Photoperiod – the number of hours of daylight between sunrise and sunset.  The earth is slightly slanted on a 23.5 degree axis and when it rotates like a spinning top, so as it is spinning counter-clockwise wobbles a little left to right.

Revolution and Rotation  Earth revolves around the sun – it takes 365 ¼ days to complete one revolution (This is why we gain one day in February every four years – the leap year).  The sun isn’t right in the middle as we rotate around it, it is actually one of two focal points – hence the earth rotates around the sun in an ellipse rather than in a perfect circle.

Revolution and Rotation  The perihelion is the point where the Earth is the closest to the sun and aphelion is when the earth is the furthest from the sun.  Note, that the Northern Hemisphere is winter when the Earth is at the perihelion and the Southern Hemisphere is summer.  Therefore, summer and winter isn’t determined how close we are to the sun, but which direction we are facing.

The Seasons  So what makes us have different seasons is not the distance from the sun, it is not the rotation of the earth (because we see the sun in the winter), it has to do with the 23.5 degree tilt of our axis.  That tilt means that during the winter in the Northern Hemisphere the earth is tilted away from the Sun, and vice versa.  Because of this tilt we have a solstices – this is when the sun is at the highest position and lowest position is the sky.  The summer solstices is the longest day of the year, (usually June 21) and the winter solstices is the shortest day of the year (usually December 21

Constellations  Astronomers have noticed different patterns in the sky that are created when you join different start with a line (like connect the dots)  The Big Dipper and Little Dipper are two of the most famous constellation  The other 12 famous constellations are the zodiac signs: Aries, Taurus, Gemini, Cancer, Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius, Pisces

Homework  Page 210 – Key ideas of Earths Revolution, The Season’s, and Constellations  Page 211 – Find the Big Dipper and Little Dipper only.