Board of Longitude chronometers, keeping) the time of the reference place when one is far away from it. For details of the efforts towards determining the longitude, see History of longitude. For many decades a sufficiently accurate chronometer was prohibitively expensive. The lunar distance method was used by mariners either in conjunction with or instead of the marine chronometer. However, with the expectation that accurate clocks would eventually become commonplace, John Harrison showed that his method was the way of the future. However the board, to its discredit, never awarded the prize to Harrison, nor anyone else. With the significant problems considered as
Mean longitude angle between any physical objects. It is simply a convenient uniform measure of how far around its orbit a body has progressed since passing the reference direction. While mean longitude measures a mean position and assumes constant speed, true longitude measures the actual longitude and assumes the body has moved with its actual speed, which varies around its elliptical orbit. The difference between the two is known as the equation of the center. From the above definitions, define the "longitude of the pericenter" Then mean longitude is also Another form often seen is the "mean longitude at epoch", "ε". This