What is the Local Meridian?

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What is the Local Meridian? The local meridian is something many have never heard of, yet it’s a pivotal element in navigation, time keeping and astronomy. It defines where you.

In simple terms the local meridian is an imaginary line that runs from north to south and goes straight over your head through what we call zenith, a point in the sky directly above you.

In addition to being a north/south line, as are all meridians, the local meridian defines midday, as it signifies the highest point the Sun and other celestial bodies will reach in their daily arc across the sky. The term “meridian” comes from the Latin meridies, which means both “midday” and “south.

The Sun, Moon and planets orbit in the same plane, which keeps them in a narrow path across the sky called the ecliptic. From the northern hemisphere we find the ecliptic in our southern sky. In the southern hemisphere, it’s in the north

  • The point in the sky directly above an observer.
  • The Sun apparent path across the celestial sphere.
  • The imaginary point in space where Earth’s rotational axis extends to the celestial sphere.
  • An imaginary sphere around the earth to which it appears to have all celestial objects projected upon.

Mariners practicing celestial navigation would take sun-angle observations when the Sun reached the local Meridian to determine their latitude.

A.M. (anti-meridian) and P.M. (post-meridian) refer to Sun’s position with respect to the local meridian. If you’re an astronomer, the best time to observe an object is when it transits the local meridian. When this occurs the object will be at its highest point in the sky and has the least amount of atmosphere between the observer and the observed object. This provides the clearest view.

As you can see, the local meridian is quite an important marker and without even knowing it, it has affected your life in numerous ways. We hope to explore this concept and more and show you how much there is to learn about what it around you.


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