​​​​​​​​​​​​Museum Of Measurement And Time

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                                    EARTH'S  ROTATION AND IT'S RELATION

                                           TO ASTRONOMY AND TIME

For purposes of this writing, we make the assumption the reader has a general understanding of earth's relation to the Sun. The North & South Poles, the equator and the terms: a year, a day, an hour, a minute and the second. It gets complicated beyond these terms. 

Earth rotates about an imaginary line between the North and South Poles. This line is called the "axis of rotation". Earth rotates about this line once each day.

This is the basis for tracking the passage of time. We will address the method to determine the location of points on the earth's sphere (Latitude & Longitude) at another time.


We will now explain the terms "Sidereal Day", the "Solar Year" and "clock Time". Before we start, we need to understand the astronomer's definition of  'rotate' and 'revolve'. To the astronomer 'rotate' is the motion of spinning around an axis that passes through a body. The term 'Revolve' means to orbit around another body. The complete passing of one orbit will equal one revolution. This concept was started in 1543, when Copernicus proposed that "the solar system revolved about the Sun". This was a radical theory and at the time was a major change in how we looked at the universe.  I wonder how this theory relates to modern astronomy? 

 The "Solar Day" is based on earth's rotation around it's axis; the "Sidereal Day" is referenced to earths rotation relative to the stars. When we divided the "Solar Day" into 24 hours, the earth will travel about 1/365th of the way around the sun (we call this "Solar Time"). There is a small difference between "Sidereal Time' and "Solar Time". The sidereal day is shorter than the solar day because earth rotates and revolves in a common - counterclockwise direction and Venus rotates in the opposite direction to its revolution. The sidereal day is longer than it's solar day.


It is not necessary to have a complete understanding of astronomy to use Burt's Solar Attachment; this reality increases my appreciation for his invention. PERHAPS WE NEED TO REMEMBER: When we seek a solution to complex issues, look for the simple solution first.

IIn the 'Northern Hemisphere' (North America): north is normally thought of as "up"; but, what about the person in the 'Southern Hemisphere'?  A person in this part of earth does not consider himself upside-down! So up and down are arbitrary designations in space. A way to keep these terms in prospective is to "make a hitchhiker fist with the right hand". With the thumb pointing up the fingers curl in the direction of earth's rotation. With this model, you always have a globe of earth.

Earth's path as it rotates around the Sun is not along a line through the center of the Sun; rather it's line of rotation is along a line approximately 1 degree above this line. Question, How would a surveyor verify the basis of this observation? This has an answer complex answer and is considered beyond this writing!


1. What we call normal time is 'Sun based time', this was adopted because most people are concerned with 'time'  when the Sun is visible than when the stars are visible. Astronomers use both "Sidereal Time" as well as "Solar Time".

2. Earth's "Solar Day" lasts 4 minutes longer than the " Sidereal Day".

3. A "Sidereal Day" is 24 sidereal hours or 23 hours, 56 minutes & 4 seconds on a normal clock.

prepared April 2014

This information, when comprehended, may create interest in other subjects. Future subjects, such as: the Gregorian Calendar and the relation of time, latitude & longitude, will be posted in the future.

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