Lunar Standstill - Other Complications

Other Complications

All discussion above refers to the Geocentric Declination, which is the declination of the Moon as viewed from the position of the centre of the Earth. However, because the Moon is relatively close to the Earth, lunar parallax causes a change of declination (up to 0.95°) when the Moon is observed from a position on the Earth's surface. Thus the geocentric declination discussed above may be up to about 0.95° different from the observed declination. Because the amount of this parallax is not the same for all maxima shown above, it may be sufficient, for example, to make the April 2006 maximum a higher declination, when viewed from a particular site, than the September 2006 maximum. Thus the date of the observed maximum will change from place to place in the world.

Another effect is atmospheric refraction - the bending of the light from the Moon as it passes through the Earth's atmosphere - which will also change the observed declination of the Moon. This is especially significant at low elevation, since the atmosphere is thicker (deeper) at lower elevations.

In addition, not all the maxima are observable from all places in the world - the Moon may be below the horizon at a particular observing site during the maximum, and by the time it rises it may have a lower declination than an observable maximum at some other date. Or the maximum may occur in the middle of the day, and thus be effectively invisible.