The Sun's declination is its angular distance north or south of the celestial equator. It varies throughout the year due to the Earth's tilt on its axis. Here's when the Sun reaches its minimum and maximum declinations:

* Minimum Declination (Winter Solstice): This occurs around December 21st or 22nd in the Northern Hemisphere. The Sun's declination is at its most negative value, which is approximately -23.44 degrees. This is when the Northern Hemisphere experiences its shortest day and longest night.

* Maximum Declination (Summer Solstice): This occurs around June 20th or 21st in the Northern Hemisphere. The Sun's declination is at its most positive value, which is approximately +23.44 degrees. This is when the Northern Hemisphere experiences its longest day and shortest night.

Note: These dates are approximate and can vary slightly from year to year.