An irregularity in the Moon's orbit, which can amount to 11 degrees in a period of one year. It results from the Sun's disturbing effect on the motion of the Moon due to varying distance between them.
The equilibrium line at the end of the mass-balance year. At the Annual equilibrium line, Annual ablation balances Annual accumulation and the Annual mass balance is zero.
Annual accumulation minus Annual ablation. Ablation is defined to be negative, so the Annual exchange may also be regarded as the sum of the absolute values of accumulation and ablation. It is a possi
ble measure of the amplitude of mass exchange between the glacier and its environment, but the mass-balance amplitude is more often used for that purpose. Formerly Annual exchange was defined only in the fixed-date system and total exchange was defined as its equivalent in the stratigraphic system.
The sum of accumulation and ablation over the mass-balance year, equivalent to the sum of Annual accumulation and Annual ablation, and also to the sum of winter mass balance and summer mass balance wh
ere winter and summer are well-differentiated; that is, ba = ca + aa = bw + bs. For reasons explained more fully under Net mass balance, the term Annual mass balance replaces the formerly distinct terms 'Annual balance' and 'net balance', which were used in the fixed-date system and the stratigraphic system respectively. The adjective 'Annual' describes the time span of the mass-balance measurement more adequately than the adjective 'net', which does not refer to a time period but rather to the mass that is remaining after all deductions (here ablation) have been made.
The difference in position of a star as seen from the Earth and Sun, i.e. the angle subtended at a star by the mean radius of the Earth's orbit around the Sun. Same as heliocentric parallax. Because
the Earth revolves around the Sun, we observe the sky from a constantly moving position in space. Therefore, we should expect to see an annual effect, in which the positions of nearby objects appear to oscillate back and forth in response to our motion around the Sun. This does in fact happen, but the distances to even the nearest stars are so great that we need to make careful observations with a telescope to detect it. The annual parallax of the nearest star, Proxima Centauri, is 0.762 arcsec, which is too small for our acuity of vision.
The snowline at the end of the ablation season, usually representing the highest position of the snowline during the mass-balance year; end-of-summer snowline is a synonym. The snowline of any given b
alance year is established at the end of that balance year. If this newly established snowline is lower than the previous year's firn line, it also becomes the new firn line.
A solar eclipse in which the Moon is close the apogee and is, therefore, too small to cover the whole disk of the Sun, leaving a visible edge or ring of sunlight. An annular eclipse can last for 12m 3
0s at the most.