When they talk about this stuff they really need to specify which “day” they’re talking about, or else for places that do so, the day the clocks go forward is the shortest day in a year with no others being close.
From another viewpoint, all rotations relative to the non-Sun stars - aka sidereal days - are still shorter. The daily movement along our orbit around the Sun contributes an extra four minutes to make up the full 24 hours.
And so, they must be talking about the solar day. They do say 24 hours after all. Or must they? The discrepancy in the nearest sidereal day will be almost exactly the same, and that rounds to 24. So for which day was the lacking one-and-a-bit milliseconds calculated for?
There’s another factor - days where thr earth is orbiting faster, eg on the closer side of the ellipse - are a different length midday to midday from when we are on the far side of the ellipse.
You can convince yourself of this when you consider that the area of the arc we traverse each day is the same (Kepler’s law). On the short side of our eliptical orbit, since the orbital distance is shorter, the arc must have a larger angle that we travel. That means the amount a point on the earth rotates to have the sun come back directly overhead must be different in different parts of the year.
This difference, summed day over day, results in a +/- 20 min movement of actual midday to 12pm. The ‘mean’ in Greenwich Mean Time refers to averaging this difference over the whole orbit.
Pedantry time!
When they talk about this stuff they really need to specify which “day” they’re talking about, or else for places that do so, the day the clocks go forward is the shortest day in a year with no others being close.
From another viewpoint, all rotations relative to the non-Sun stars - aka sidereal days - are still shorter. The daily movement along our orbit around the Sun contributes an extra four minutes to make up the full 24 hours.
And so, they must be talking about the solar day. They do say 24 hours after all. Or must they? The discrepancy in the nearest sidereal day will be almost exactly the same, and that rounds to 24. So for which day was the lacking one-and-a-bit milliseconds calculated for?
There’s another factor - days where thr earth is orbiting faster, eg on the closer side of the ellipse - are a different length midday to midday from when we are on the far side of the ellipse.
You can convince yourself of this when you consider that the area of the arc we traverse each day is the same (Kepler’s law). On the short side of our eliptical orbit, since the orbital distance is shorter, the arc must have a larger angle that we travel. That means the amount a point on the earth rotates to have the sun come back directly overhead must be different in different parts of the year.
This difference, summed day over day, results in a +/- 20 min movement of actual midday to 12pm. The ‘mean’ in Greenwich Mean Time refers to averaging this difference over the whole orbit.