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Secular acceleration in astronomy refers to a continuous and non-periodic change in the orbital velocity of one celestial body around another or the axial rotation period of a celestial body. Unlike periodic variations, secular acceleration represents a long-term, sustained change.
An example of secular acceleration is observed in the axial rotation of the Earth. The Earth’s rotation period is gradually slowing down over time, and this phenomenon is attributed to the gravitational effects of the Moon. The key contributing factor is the gravitational interaction between the Earth and the Moon, leading to the generation of tides on Earth.
The mechanism involves tidal forces causing friction between the Earth and the ocean waters, resulting in a transfer of angular momentum. While the Earth experiences a gradual slowing of its axial rotation, the lost momentum is transferred to the Moon. As a consequence, the Moon’s orbital period increases, and it gradually moves away from the Earth.
The overall effect of secular acceleration in the Earth-Moon system includes:
- Earth’s Axial Rotation: The Earth’s axial rotation period is increasing over time.
- Moon’s Orbital Period: The Moon’s orbital period is also increasing.
- Moon’s Recession: The Moon is receding from the Earth at a measurable rate.
As a specific example, the Earth’s axial rotation period is increasing by approximately 15 millionths of a second per year, and the Moon is receding from the Earth at a rate of about 4 cm (1.5 inches) per year.
Secular acceleration phenomena are important considerations in celestial mechanics and contribute to our understanding of the long-term dynamics of celestial bodies in gravitational systems.