Word origin · etymology
Historical mathematical phrase.
Equation here uses the older astronomical sense of a correction or adjustment, not simply a statement that two expressions are equal.
How we know · epistemology
Astronomical time correction
Earth's orbital geometry produces a calculable difference between apparent and mean solar time. Sources may reverse the subtraction order; comparing numerical values requires checking the sign convention before applying the correction.
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These links connect subjects and terminology. They do not establish a shared historical origin.
Sources & provenance
Use the citations beside each section to distinguish a calculation convention, a historical teaching and an editorial example.