Celestial Motions

Ecliptic

The Sun is orbiting inside of the milky way and is going to vega (antapex). If you were to look in the other direction, the Sun would be going away from other stars (apex). However, the stars are not in fact moving away from each other, making this motion apparent.

Modern astronomers have recognized a point of apparent star diversion (apex) and a point of star conversion (antapex) 180° apart in the sky

STARS

Celestial Motions

The Sun appears to move across the sky throughout the course of a year.

The Sun's ecliptic motion is actually apparent as it's Earth that moves along its orbit and causes our vantage point of the Sun to change so it looks as if the Sun is moving.

Diurnal is an apparent motion because we see the sun, moons, stars and planets move east to west as a result of Earth moving west to east on its axis.

The sun, moon, stars, and planets appear to rise in the east and set in the west.

Diurnal

Real

and

Apparent

MOTIONS

Where an object moves around a point in space on a gravitationally curved path.

In our case, the planets revolve around the Sun.

ORBITS

Orbits are real because Earth orbits around the Sun with gravity holding it in place. Without gravity, Earth would float around.

Proper Motion is apparent because Earth revolves round the Sun in actuality, but it looks as if the stars revolve around us.

This is the angular change in a position over time. The stars are in a different place each year at the same time.

MOTION

PROPER

This motion is real as the moon actually moves along with Earth during its orbit so it is able to realign with the Sun, thus completing its orbit.

This is also the time between new moons and full moons.

The time it takes for the moon to orbit Earth and to realign with the Sun.

SYNODIC PERIOD

This is apparent as the analemma is actually formed from the elliptical orbit of Earth around the Sun to make it seem like the Sun is moving when it is Earth moving.

ANALEMMA

Over the course of the year, at the same time of day, the sun appears to move in a figure 8 shape.

What are Celestial Motions?

Eclipses are a real motion because the Sun, moon and Earth all line up in a straight line. Their orbits must coincide with one another to produce the effect.

Celestial Motions are movements of any naturally occurring object found in the Universe (called a celestial body).

ECLIPSES

The moon passes in between the Earth and Sun to cause a solar eclipse.

Earth comes between the Sun and moon to cause a lunar eclipse.

The celestial equator lies along the celestial sphere in the same plane as Earth's equator.

The poles of the sphere are aligned with that of Earth's.

It's an imaginary sphere of gigantic radius with Earth at the center.

Celestial Sphere

When looking at a planet in the sky, it will follow the normal east to west movement, but sometimes it looks as if it stops moving, then move in the opposite direction.

RETROGRADE

Retrograde is apparent because Earth moves faster along its orbit than a superior planet so when it goes behind the planet, the planet goes in one direction, but when Earth passes, it looks as if its going in another direction.

CONCLUSION

Overall there are many celestial motions that make our universe what it is today.

SIDEREAL PERIOD

The sidereal period is the time that the moon takes to orbit around Earth relative to the stars.

This motion is real as it is supported be Earth revolving around the Sun. The phases of the moon occur at different places in the month because Earth orbits the sun.

The period lasts for 27.2 days.

photo credit Nasa / Goddard Space Flight Center / Reto Stöckli