Understanding the Night Sky PDF

Understanding the Night Sky 1. Motion of the Earth ○ Due to the motion of the earth and things around us, objects in the universe seem to be constantly changing. ○ The motion of celestial objects seems very slow and looks stationary relative to the earth ○ The Earth...

Understanding the Night Sky 1. Motion of the Earth ○ Due to the motion of the earth and things around us, objects in the universe seem to be constantly changing. ○ The motion of celestial objects seems very slow and looks stationary relative to the earth ○ The Earth has six different types of motion. Some objects move on a constant basis that we can observe their periods while some have a large orbit and seem to move very slowly so that their orbital period cannot be observed in our lifetime The six different motions of the earth are: 1. Rotation Movement of the earth around its axis every 23 hours 56 minutes The reason why the day is 24 hours is that the earth revolves around the sun while the moon revolves around the Earth. By taking a fixed star as a point of reference, the earth to make one rotation around its axis, and the moon to have revolved around the Earth, the Earth should have moved an additional 4 minutes on its orbit.  2. Orbit It takes 365,25 days for the Earth to make one trip 3.Precession ○ Due to the gravitational pull of other planets, mainly Jupiter and Venus, the Earth's equatorial bulge, and the conservation of angular momentum, the Earth gradually wobbles off the rotational axis. ○ This motion has to do with the climate of the earth ○ The axis of rotation slowly precess around and it takes 26 000 years to make one complete rotation. ○ As a result of precession the polar star of the earth keeps on changing. 4.Motion around the Barycenter ○ Due to the force of attraction between two bodies, the two bodies revolve around a common center called the Barycentre(the center of the masses of the two bodies). The force of attraction between the Earth and the moon results in a wavy motion of the Earth around the sun 5.Ellipticity(degree of deviation from the center) ○ Sometimes the Earth has a more circular orbit while some other times a more elliptical orbit ○ The change in the ellipticity of the orbit of the Earth causes ice ages (a circle of 10 000years) 6.Tilt ○ The tilt of the Earth changes between 210 and 240relative to the true north ○ The circle takes about 41 000 years and it also affects climate change. All this motion has an effect on how we observe the Universe. The different locations on the Earth also have a different perspective on the Universe.