Physical Constants Aren’t Constant
Obliquity of the Ecliptic
Wednesday, September 1, 1976
The Vangelis track “Albedo 0.39” released in Sept 1976, told us that the obliquity of the ecliptic was 23°27′8.26″
But apparently that is no longer true!
Earth's obliquity oscillates between 22.1 and 24.5 degrees on a 41,000-year cycle.
Based on a complicated equation, the Earth’s obliquity is continuously updated by the Jet Propulsion Labs;
ε = 23°26′21.406″ − 46.836769″ T − 0.0001831″ T2 + 0.00200340″ T3 − 0.576×10−6″ T4 − 4.34×10−8″ T5
As of 2021 Earth's mean obliquity was 84381.4 arcsec, or 23°26′21.4″
(or 23.439°) and decreasing.
Earth’s albedo was determined in the 1970s to be 0.39, but since the Vangelis album’s release, it has also changed to 0.30.
Interestingly, the Astronomical Unit is defined as the mean distance from the Sun, which according to Vangelis was 92,957,200 miles. This value used to vary depending on the length of the day and other factors.
Since then 1AU has been fixed at a value of 149,597,870,700 meters, or 92,955,807.3 miles
Thankfully, JPL tells us that the speed of light in a vacuum is still 299,792,458 m/s. I guess some things never change.