==================
The Local Meridian
==================

         **Jason Harris**

         The Local Meridian is an imaginary :doc:`Great
         Circle  <ai-greatcircle>` on the :doc:`Celestial
         Sphere  <ai-csphere>` that is perpendicular to the local
         :doc:`Horizon  <ai-horizon>`. It passes through the North
         point on the Horizon, through the :doc:`Celestial
         Pole  <ai-cpoles>`, up to the
         :doc:`Zenith  <ai-zenith>`, and through the South point on the
         Horizon.

         Because it is fixed to the local Horizon, stars will appear to
         drift past the Local Meridian as the Earth spins. You can use
         an object's :ref:`Right Ascension <ai-skycoords-equatorial>`
         and the :doc:`Local Sidereal Time  <ai-sidereal>` to determine
         when it will cross your Local Meridian (see :doc:`Hour
         Angle  <ai-hourangle>`).