Is it possible that in 13,000 years it will be summer in December in the northern hemisphere? Or do we artificially change the definition of the length of the year to ensure this never happens?

The Great Year of about 26000 years is the period for this

retrograde time motion that is attributed to the precession motion of

the Earth's tilt ( polar ) axis. In half of this period, we go back in time,

from solstice to summer and vice versa.

To neutralize this effect for our future generations,

we can DELAY EVERY NEW YEAR# by

#20 min 14 sec /year.

Yes, the precession of the Earth's axis and its axial tilt can cause the seasons to vary over very long periods of time. This phenomenon is called axial precession, and it causes the axis's orientation to change gradually over time, changing the timing of the seasons. But we do not artificially change the definition of the year so that summer does not occur in December in the northern hemisphere.

It is not possible for it to be summer in December in the northern hemisphere due to the way we define the length of the year. Our calendar system, including the definition of seasons, is based on the Earth's orbit around the Sun, which takes approximately 365.25 days. This orbit defines the timing of the seasons such that summer occurs during the months of June, July, and August in the northern hemisphere, while December falls within the winter season. This definition is not subject to artificial changes but rather reflects the natural phenomena of Earth's orbit and axial tilt. Therefore, it is highly unlikely that summer would occur in December in the northern hemisphere under our current calendar system and astronomical understanding.