# Solar day and the amount of Earth's rotation

• james gander
In summary, the conversation discusses the difference between a solar day and a sidereal day, with the latter being defined by the position of the stars and the former being defined by the position of the sun. The confusion arises from the fact that the Earth rotates a little more than 360 degrees in a solar day due to its orbit around the sun. This is similar to how the hands of a clock move, with the minute hand representing the sidereal day and the hour hand representing the solar day. It is also mentioned that every year has one less solar day than sidereal days. Google initially caused confusion by stating that the Earth rotates exactly 360 degrees in a solar day, but this is not entirely accurate. The Earth actually rotates about
james gander
Hi. I am confused about something and it is making me feel rather stupid.

First of all i will explain what i know. I know a solar day is 24hrs long and it is defined by the position of the sun. I also know a sidereal day is 23h 56m and is defined by the postition of the stars (basically).

The problem i have is with the solar day. As the Earth rotates it also orbits the sun, and because of that orbit the Earth has to rotate a little further each day. If it didnt then the sun would be in a different place.

I can see in a sidereal day the Earth roates 360 deg, however a solar day must be more then 360 degrees surely?

Sorry for such an infantile question but is it just simply that a the Earth rotates more then 360 in a solar day?

james gander said:
is it just simply that a the Earth rotates more then 360 in a solar day?
Yes.

This is similar to how hands of a clock move. Imagine both hands of the clock start at 12 o'clock.
Think of how far the minute hand moves in an hour (back to the number 12 on the clock). This is analogous to the sidereal day, as the numbers are static, just like the background stars.
Now think how far it has to move to catch up with the hour hand. This is analogous to the solar day, where the hour hand represents the sun moving across the sky w/r to the fixed stars, due to Earth's orbit.

Every full 12 hours, the hands meet only 11 times. Similarly, every year has exactly one less solar day than sidereal days (ignoring other factors, like precession of equinoxes).

Bandersnatch said:
Yes.

This is similar to how hands of a clock move. Imagine both hands of the clock start at 12 o'clock.
Think of how far the minute hand moves in an hour (back to the number 12 on the clock). This is analogous to the sidereal day, as the numbers are static, just like the background stars.
Now think how far it has to move to catch up with the hour hand. This is analogous to the solar day, where the hour hand represents the sun moving across the sky w/r to the fixed stars, due to Earth's orbit.

Every full 12 hours, the hands meet only 11 times. Similarly, every year has exactly one less solar day than sidereal days (ignoring other factors, like precession of equinoxes).
Yes thought so , just thought i would check. Google says the Earth rotates 360 degrees in a solar day and that is what was annoying me. thanks

Just to confirm. The Earth rotates on its axis by approximately (24*60*60)/(23*60*60+56*60) * 360 = 361.0 degrees in a solar day.

phyzguy said:
Just to confirm. The Earth rotates on its axis by approximately (24*60*60)/(23*60*60+56*60) * 360 = 361.0 degrees in a solar day.
Rotates with respect to what?

With respect to inertial space, yes, the Earth rotates by about 361 degrees in a mean solar day (86400 seconds). But with respect to the Sun, the Earth rotates by about 360 degrees in a mean solar day.

D H said:
Rotates with respect to what?

With respect to inertial space, yes, the Earth rotates by about 361 degrees in a mean solar day (86400 seconds). But with respect to the Sun, the Earth rotates by about 360 degrees in a mean solar day.

Agreed.

## 1. What is a solar day?

A solar day refers to the amount of time it takes for the Earth to complete one rotation on its axis relative to the position of the sun. It is approximately 24 hours long.

## 2. How does the solar day compare to the sidereal day?

The solar day is slightly longer than the sidereal day, which is the amount of time it takes for the Earth to complete one rotation relative to the stars. This is because the Earth also moves along its orbit around the sun, causing the sun to appear to shift position in the sky.

## 3. How does the length of a solar day change throughout the year?

The length of a solar day varies slightly throughout the year due to the Earth's elliptical orbit around the sun. When the Earth is closer to the sun, it moves faster in its orbit, resulting in slightly shorter solar days. When the Earth is farther from the sun, it moves slower and solar days are slightly longer.

## 4. Are solar days consistent across the entire Earth's surface?

No, solar days are not consistent across the entire Earth's surface. The Earth's rotation is affected by factors such as its tilt, the distribution of land and water, and the Earth's shape. This results in variations in the length of a solar day at different latitudes.

## 5. How do scientists measure the amount of Earth's rotation?

Scientists use a variety of methods to measure the Earth's rotation, including astronomical observations, atomic clocks, and global positioning systems. These measurements are used to track changes in the length of the day and to make adjustments to our timekeeping systems.

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