OBSERVATIONS FOR TIME AND LONGITUDE, 
175 
Predictions of Oceultations. 
The f Nautical Almanac * gives the elements of oceultations as they would 
he seen from the centre of the Earth, and although the limits of latitudes 
between which the star may be occulted are stated, this does not mean 
that the star will be occulted as seen from every place within the limits 
stated, but rather that outside these limits the star cannot be occulted. 
Again, although an occultation may be visible, the star’s apparent path 
may so approach a tangent to the moon’s disc as to render the results 
obtained from the observation of such an occultation unreliable. The time 
of occultation may, owing to the effects of parallax, be any time from 
about two hours before to the same interval after the time of conjunction 
as given in the f Nautical Almanac.’ These circumstances render it 
desirable to determine, before attempting to observe an occultation, 
whether the star as seen from the observer’s station will be occulted at 
all, and if so, at what time approximately it may be looked for, and at 
what portion of the moon’s disc the star will disappear and reappear. 
The simplest way of doing this is to draw to scale the position of the 
star, and relatively to it the path of the moon as affected by parallax. 
