Is a sidereal day longer or shorter than a solar day?

Answer 1

The Sun crosses the meridian (the imaginaryline in the sky from due north to due south and passing directly overhead) at solar noon. The period between two successive solar noons is a "solar day".

When you reckon the period of time between two successive meridian transits of a distant star, or the vernal equinox, that is a "sidereal day".

In simple terms the sidereal day is the rotation period of a planet.

Answer 2

The Earth's "sidereal day" is simply the planet's rotation period. This is not affected by the Earth's orbiting the Sun.

The Earth's "solar day" is about 4 minutes longer than the sidereal day, and this is affected by the Earth's orbital motion. The solar day is based on the Sun's position in the sky.

The Sun seems tomove slowly eastwards across the sky during the year because of the Earth's changing position as it orbits. So, each day the Earth has to rotate for aboutan extra 4 minutes to get the Sun back in the same place in the sky. I won't go into the exact definitions here, but that's thebasic idea.

Answer 3

Because a sidereal day is determined by the direction one part of the Earth is pointing to. This direction is always the same. However, with solar days, that part has to point at the sun. From the direction the earth is pointing to, to the part of the earth that is pointing towards the sun, the difference is 1 degree. This is roughly 4 minutes more. That's why the solar day is longer.

Answer 4

The sidereal day is about 243 Earth days. That is the time for the planet to

rotate once .

The solar day is 117 Earth days,roughly. That is a big difference. On Earth

the difference between these two days is only about 4 minutes.

The reason for the big difference on Venus is that Venus rotates very slowly.

The solar day depends on the rotation of a planet AND its orbital motion.

The slow rotation makes the effect of the orbital motion much greater on

the length of the solar day.

Incidentally Venus rotates in the opposite direction to Earth. That's why

the solar day is shorter than the sidereal day. On Earth it's the other

way round.

Answer 5

On Earth, a sidereal day is shorter than a solar day. The sidereal day is 23 hours 56 minutes and some odd seconds. This is the time it takes for the Earth to rotate once on its axis relative to the far distant stars. In this period of time, the Earth also revolves around the Sun a little bit, enough to require nearly four additional minutes for the Earth to "catch up" with the Sun and arrive at the same point relative to the Sun, completing its Solar day.

For most planets this is typical. However for a planet like Venus, which has "retrograde" rotation, the sidereal day is the longer day.

Answer 6

A sidereal day is 23 hours 56 minutes, which the period the Earth rotates in, relative to the stars. It takes another 4 minutes for the Sun to cross the meridian as it did yesterday, because, since yesterday, we have moved 1 degree round our orbit.

Answer 7

Normally a sidereal day is just a bit shorter than a solar day, but because the direction of the rotation of Venus is opposite the direction of its revolution, and because it takes more time for Venus to complete one sidereal rotation than to complete one orbit of the sun, a sidereal day on Venus is 108% longer than a solar day on Venus.

Answer 8

A solar day is usually longer. However a planet like Venus has a longer sidereal day than solar day. That's because of its "retrograde" rotation.