Sky Watching

1. Horizon: The horizon is the line where the sky seems to meet the ground. When you stand still and turn around, the horizon looks like a circle surrounding you.

2. Celestial Sphere: The sky appears like a giant sphere around the Earth, called the celestial sphere, on which stars and planets seem to move.

3. Zenith and Nadir:

• Zenith: The point directly above your head on the celestial sphere.
• Nadir: The point directly under your feet on the celestial sphere.

4. Celestial Poles: When Earth's rotation axis is extended into the sky, it intersects the celestial sphere at the North and South celestial poles.

5. Meridian: A circle passing through the celestial poles, zenith, and nadir is called the meridian.

6. Celestial Equator: If Earth's equator is extended outward, it forms the celestial equator on the celestial sphere.

7. Ecliptic: The ecliptic is the path the Sun seems to follow on the celestial sphere throughout the year, caused by Earth’s orbit around the Sun.

8. Sky and Space:

• Sky: The part of the atmosphere and beyond that looks like a roof above us.
• Space: The empty area between stars and planets, containing gas, dust, and star clusters.

9. Motion of Celestial Bodies:

• The Sun, Moon, and stars rise in the east and set in the west because Earth rotates from west to east.
• Stars rise 4 minutes earlier each day, and the Sun moves 1 degree daily, while the Moon moves 12–13 degrees daily, due to their motion relative to Earth.

Virtual sphere