| s | $t=d/v$ | time = distance [m] / speed of light (3x10⁸) [m/s] |
|---|---|---|
| m/s | $v=\frac{2πr}{T}$ | speed = circumference of orbit [m] / orbital period [s] |
| 1/s | $H_0=\frac{v}{d}$ | hubble constant = velocity of an object moving away [km/s] / distance between [km] |
| $\frac{1}{H_0}=\frac{d}{v}$ | age of universe. |
Earth rotates on its axis once every 24 hours. Causing day and night.
Earth orbits around the Sun once every 365 days.
Earth’s axis is a line passes through the North and South poles, titled at an angle of approximately 23.5° from the vertical.
Sun always appears: Rise from the East, Set in the West. Reaching highest point at noon.
The Moon is a natural satellite.
Takes about one month to complete one orbit around the Earth. (28 days)
Rotates on its axis once every 28 days also, so the same side always faces the Earth.
Moon doesn’t produce its own light.
Visible in the night sky because it reflects the light from the Sun.
As it orbits around the Earth, it undergoes different phases.
