Definition of LMT
Local Mean Time (LMT) at any instant is the arc of the equator, or the angle at the pole, measured westerly from the inferior meridian of the observer to the meridian of the sun at that instant, expressed in units of time from 0 to 24 hours.
Definition of GMT
Greenwich Mean Time (GMT) at any instant is the arc of the equator, or the angle at the pole, measured westerly from the 180° meridian to the meridian of the sun at that instant, expressed in units of time from 0 to 24 hours.
Definition of GHA
Greenwich Hour Angle or GHA of a celestial body is the arc of the equinoctial, or the angle at the celestial pole, measured westerly from the celestial meridian of Greenwich to the celestial meridian of the CB, expressed in degrees & minutes of arc from 0° to 360°.
Definition of LHA
Local Hour Angle or LHA of a celestial body is the arc of the equinoctial, or the angle at the celestial pole, measured westerly from the observer’s celestial meridian to the celestial meridian passing through that body. Like GHA, LHA of a celestial body would increase steadily from 0° to 360°. LHA would be 0° when the body is on the observer’s meridian and steadily increase until it is 360° (i.e. 0°) when it would again be on the observer’s meridian.
Relationship between GHA of the sun & GMT
Both GMT & GHA of the sun are measured westerly in a full circle, expressed in units of time from 00h to 24h whereas GHA of the sun is usually expressed in degrees from 0° to 360° but may, when necessary, be expressed in units of time from 00h to 24h. The big difference is that GMT is measured westerly from the inferior meridian of Greenwich, which is 180° longitude, whereas GHA of the sun is measured westerly from the Greenwich (superior) meridian. Hence, GMT = GHA sun ± 12 hours
Relationship between LHA of the sun & LMT
Both LMT & LHA of the sun are measured westerly in a full circle – LMT is expressed in units of time from 00h to 24h whereas LHA of the sun is usually expressed in degrees from 0° to 360° but may, when necessary, be expressed in units of time from 00h to 24h. The big difference is that LMT is measured westerly from the inferior meridian of the observer, whereas LHA of the sun is measured westerly from the Observer’s (superior) meridian. Hence, LMT = LHA sun ± 12 hours
