Solar Day & Sidereal Day.pptx

Science

1. Solar Day & Sidereal Day By S.SRIKUMAR X - A

2. Solar Day The period for a celestial object to rotate once in relation to the star it is orbiting is called Solar Day. It is the basis of solar time. It is also known as a Synodic Day. The time taken to complete 1 Solar Day is called Synodic Rotation Period.

3. Earth’s Solar Day The time it takes for the Sun to pass over the same meridian is called Earth’s Solar (or) Synodic Day. 1 Solar Day on Earth has a time duration of 24 hours. This time duration is not constant and changes over the course of the year due to the eccentricity of the Earth’s orbit around the Sun & the axial tilt of the Earth.

4. The longest & shortest synodic days’ durations differ by about 51 seconds. As viewed from the Earth during the year, the Sun appears to slowly drift along an imaginary path coplanar with Earth’s orbit, known as the ecliptic, on a spherical background of seemingly fixed stars. Each synodic day, this gradual motion is a little less than 1° eastward (360° per 365.25 days), in a manner known as prograde motion.

5. Certain orbits & sun- synchronous orbits have orbital periods that are a fraction of a synodic day. Combined with a nodal precession , this allows them to always pass over a location on Earth’s surface at the same mean solar time.

6. A Synodic Day In Other Planets Due to tidal locking with the Earth, The Moon’s Synodic Day (or) Lunar Day is the same as its synodic period with Earth & the Sun. Due to the slow rotational speed & retrograde motion of Venus, its synodic rotation period of 117 Earth Days is about half the length of its orbital period & sidereal rotational period. Due to the slow rotational speed & orbit around the Sun of Mercury, its synodic rotation period of 176 Earth Days is 3 times longer than its sidereal rotational period and twice as long as its orbital period.

7. Sidereal Day Sidereal time is a timekeeping system that astronomers use to locate celestial objects. Using sidereal time, it is possible to easily point a telescope to the proper coordinates in the night sky. Viewed from the same location, a star seen at one position in the sky will be seen at the same position on another night at the same sidereal time.

8. More exactly, sidereal time is the angle measured along the celestial equator from the observer’s meridian to the great circle that passes through the March Equinox & both equinoxes, and is usually expressed in hours, minutes & seconds. 1 Sidereal Day on Earth has a time duration of 23 hours, 56 minutes & 4.0905 seconds.

9. Because Earth orbits the Sun once a year, the sidereal time at any given place & time will gain about 4 minutes against every local civil time, every 24 hours, until, after a year has passed, 1 additional sidereal day has elapsed compared to the number of solar days that have gone by. The sidereal day is the time it takes for the Earth to complete 1 rotation about its axis with respect to the stars. A measurement of the sidereal day is made by noting the time at which a particular star passes the celestial meridian(i.e., directly overhead) on 2 successive nights.

10. Fun Fact Q : Why are different constellations visible at only specific times of the year? ANS : Because as we can see, our usual definition of an Earth Day is 24 hours, so the sidereal day is 4 minutes faster. This means that a particular star will rise 4 minutes earlier every night, and this is the reason why different constellations are only visible at only specific times of the year.