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Katie F
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And what's the difference? I'm a bit confused 
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Elizabeth H
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Sundials and Apparent Solar Time
The Earth makes a complete rotation about its axis in 24 hours and hence, turns by 15 degrees every hour. Hence, by making a flat circular disk divided into sectors of 15 degrees and aligning the axis of the disk with the axis of Earth's rotation, one would be able to read the hour using the shadow of the vertical rod placed at the center of the disk. This is the principle behind sundials.
Sundials measure time based on the actual position of the Sun in the local sky. This time is called the apparent (or local) solar time. Noon is the precise moment when the Sun is on the meridian (which is an imaginary line passing from north to south through the zenith) and the sundial casts its shortest shadow. Before noon, when the Sun is on its way to meridian, the apparent solar time is ante meridian (a.m.) and past noon the apparent solar time is post meridian (p.m.).
Sidereal time
All astronomical objects pass across the sky through the meridian like the Sun due to the Earth's rotation. However, the Earth in addition to rotation around its axis, also revolves around the Sun. During the course of a year, due to its orbit, the Earth makes one additional rotation around the Sun. Hence relative to the stars, there is one extra rotation per year, and this amounts to a difference in the position of the stars in the sky by about four minutes of time, when viewed at the same time on two successive days.
Thus, relative to the stars, the Earth's rotation period is about 23 hours and 56 minutes (more accurately 23 hours, 56 minutes and 4.09 seconds), or 4 minutes less than 24 hours. This time period is called a sidereal day and clocks running at this rate indicate the sidereal time. The sidereal clock is defined to be 0 h at noon on Spring Equinox, and it coincides with the solar time at Autumn Equinox. The sidereal time is invaluable to amateur and professional astronomers to orient star maps to the sky and to point telescopes.
The Earth makes a complete rotation about its axis in 24 hours and hence, turns by 15 degrees every hour. Hence, by making a flat circular disk divided into sectors of 15 degrees and aligning the axis of the disk with the axis of Earth's rotation, one would be able to read the hour using the shadow of the vertical rod placed at the center of the disk. This is the principle behind sundials.
Sundials measure time based on the actual position of the Sun in the local sky. This time is called the apparent (or local) solar time. Noon is the precise moment when the Sun is on the meridian (which is an imaginary line passing from north to south through the zenith) and the sundial casts its shortest shadow. Before noon, when the Sun is on its way to meridian, the apparent solar time is ante meridian (a.m.) and past noon the apparent solar time is post meridian (p.m.).
Sidereal time
All astronomical objects pass across the sky through the meridian like the Sun due to the Earth's rotation. However, the Earth in addition to rotation around its axis, also revolves around the Sun. During the course of a year, due to its orbit, the Earth makes one additional rotation around the Sun. Hence relative to the stars, there is one extra rotation per year, and this amounts to a difference in the position of the stars in the sky by about four minutes of time, when viewed at the same time on two successive days.
Thus, relative to the stars, the Earth's rotation period is about 23 hours and 56 minutes (more accurately 23 hours, 56 minutes and 4.09 seconds), or 4 minutes less than 24 hours. This time period is called a sidereal day and clocks running at this rate indicate the sidereal time. The sidereal clock is defined to be 0 h at noon on Spring Equinox, and it coincides with the solar time at Autumn Equinox. The sidereal time is invaluable to amateur and professional astronomers to orient star maps to the sky and to point telescopes.
E
Elizabeth H
Guest
Sundials and Apparent Solar Time
The Earth makes a complete rotation about its axis in 24 hours and hence, turns by 15 degrees every hour. Hence, by making a flat circular disk divided into sectors of 15 degrees and aligning the axis of the disk with the axis of Earth's rotation, one would be able to read the hour using the shadow of the vertical rod placed at the center of the disk. This is the principle behind sundials.
Sundials measure time based on the actual position of the Sun in the local sky. This time is called the apparent (or local) solar time. Noon is the precise moment when the Sun is on the meridian (which is an imaginary line passing from north to south through the zenith) and the sundial casts its shortest shadow. Before noon, when the Sun is on its way to meridian, the apparent solar time is ante meridian (a.m.) and past noon the apparent solar time is post meridian (p.m.).
Sidereal time
All astronomical objects pass across the sky through the meridian like the Sun due to the Earth's rotation. However, the Earth in addition to rotation around its axis, also revolves around the Sun. During the course of a year, due to its orbit, the Earth makes one additional rotation around the Sun. Hence relative to the stars, there is one extra rotation per year, and this amounts to a difference in the position of the stars in the sky by about four minutes of time, when viewed at the same time on two successive days.
Thus, relative to the stars, the Earth's rotation period is about 23 hours and 56 minutes (more accurately 23 hours, 56 minutes and 4.09 seconds), or 4 minutes less than 24 hours. This time period is called a sidereal day and clocks running at this rate indicate the sidereal time. The sidereal clock is defined to be 0 h at noon on Spring Equinox, and it coincides with the solar time at Autumn Equinox. The sidereal time is invaluable to amateur and professional astronomers to orient star maps to the sky and to point telescopes.
The Earth makes a complete rotation about its axis in 24 hours and hence, turns by 15 degrees every hour. Hence, by making a flat circular disk divided into sectors of 15 degrees and aligning the axis of the disk with the axis of Earth's rotation, one would be able to read the hour using the shadow of the vertical rod placed at the center of the disk. This is the principle behind sundials.
Sundials measure time based on the actual position of the Sun in the local sky. This time is called the apparent (or local) solar time. Noon is the precise moment when the Sun is on the meridian (which is an imaginary line passing from north to south through the zenith) and the sundial casts its shortest shadow. Before noon, when the Sun is on its way to meridian, the apparent solar time is ante meridian (a.m.) and past noon the apparent solar time is post meridian (p.m.).
Sidereal time
All astronomical objects pass across the sky through the meridian like the Sun due to the Earth's rotation. However, the Earth in addition to rotation around its axis, also revolves around the Sun. During the course of a year, due to its orbit, the Earth makes one additional rotation around the Sun. Hence relative to the stars, there is one extra rotation per year, and this amounts to a difference in the position of the stars in the sky by about four minutes of time, when viewed at the same time on two successive days.
Thus, relative to the stars, the Earth's rotation period is about 23 hours and 56 minutes (more accurately 23 hours, 56 minutes and 4.09 seconds), or 4 minutes less than 24 hours. This time period is called a sidereal day and clocks running at this rate indicate the sidereal time. The sidereal clock is defined to be 0 h at noon on Spring Equinox, and it coincides with the solar time at Autumn Equinox. The sidereal time is invaluable to amateur and professional astronomers to orient star maps to the sky and to point telescopes.