# Exploring the Ecliptic Plane's Tilt

• JeffOCA
In summary: Therefore, we cannot have ψ = ε = 23°27'. Both circles do cross the ecliptic at a constant angle of 23°27', but they are not always parallel to each other.
JeffOCA
Hi,

1/ The ecliptic plane is tilted at a constant angle (23,45°) as compared to the celestial equator. So, why the angle between ecliptic and equator is +23,45° at spring equinox and -23,45° at autumnal equinox ?

2/ On this document, ε = 23°27'. Why don't we have ψ = ε = 23°27' ? The equator circle and the little circle (which passes through the Sun S and is parallel to equator) cross the ecliptic at a constant angle 23°27' ?

Thanks for helping

.Answer: 1/ The angle between the ecliptic and the celestial equator is +23,45° at spring equinox because the Earth's axis of rotation is tilted 23.45 degrees from the plane of its orbit around the Sun (the ecliptic plane). This tilt causes the amount of daylight to be different at different times of the year, and the Sun is directly overhead at the equator twice per year, at the spring and autumn equinoxes. During the spring equinox, the Sun is directly overhead at the equator and is also on the ecliptic plane, so the angle between the ecliptic and the equator is +23.45°. During the autumnal equinox, the Sun is still directly overhead at the equator but is on the opposite side of the ecliptic plane, so the angle between the ecliptic and the equator is -23.45°. 2/ ε is the angle between the ecliptic and the equator, which is constant at 23°27'. ψ is the angle between the equator and the little circle that passes through the Sun S and is parallel to the equator. This angle varies depending on the position of the Sun in its orbit around the Earth and is not necessarily equal to ε.

## 1. What is the ecliptic plane's tilt?

The ecliptic plane's tilt refers to the angle at which the Earth's rotational axis is tilted in relation to its orbit around the sun. This tilt is approximately 23.5 degrees and is the reason for the changing seasons on Earth.

## 2. How does the ecliptic plane's tilt affect our view of the stars?

The tilt of the ecliptic plane affects our view of the stars because it determines the path that the sun, moon, and planets appear to take across the sky. This path is known as the ecliptic and is tilted at the same angle as the Earth's rotational axis.

## 3. Why is it important to explore the ecliptic plane's tilt?

Exploring the ecliptic plane's tilt is important for understanding the Earth's position in relation to the sun and how this affects our climate and seasons. It also helps astronomers understand the movement of celestial bodies and how they appear in the night sky.

## 4. How is the ecliptic plane's tilt measured?

The ecliptic plane's tilt is measured using a coordinate system called the celestial sphere. This system divides the sky into two hemispheres and uses the ecliptic as its reference point. The angle of the tilt is measured in degrees, with 0 degrees being the celestial equator and 90 degrees being the north celestial pole.

## 5. Does the ecliptic plane's tilt change over time?

Yes, the ecliptic plane's tilt does change over time due to a phenomenon known as precession. This is caused by the gravitational pull of the moon and sun on the Earth's equatorial bulge, causing the rotational axis to slowly shift over a period of approximately 26,000 years.

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