Final answer:
At the equinoxes, the Sun is at approximately 0h or 12h RA and 0° declination, while at the solstices, it is at approximately 6h or 18h RA and +/-23.5° declination.
Step-by-step explanation:
To explore the variations in right ascension (RA) and declination of the Sun during the equinoxes and solstices, we need to understand their significance in the celestial coordinate system.
Right ascension is similar to longitude on Earth, except it begins at the vernal equinox, where the ecliptic crosses the celestial equator, and is expressed either in degrees or time due to Earth's daily rotation. Declination is the angular distance north or south of the celestial equator and is akin to latitude.
During the equinoxes, which occur around March 21 and September 22, the Earth's axis is perpendicular to the Earth-Sun line, resulting in the Sun being located at the celestial equator (0° declination). The RA of the Sun at these times is approximately 0h at the vernal equinox and 12h at the autumnal equinox.
On the other hand, at the solstices, the tilt of Earth's axis causes the Sun to appear at its maximum angular distance from the celestial equator.
Around June 21, the summer solstice, the Sun reaches a declination of approximately +23.5°, corresponding to the RA of 6h. Around December 21, the winter solstice, the Sun's declination is around -23.5°, with the RA at approximately 18h.
The tilt of Earth's axis directly impacts these celestial coordinates, influencing the Sun's apparent position and thus contributing to the changing seasons. In essence, these coordinates and the underlying celestial mechanics are fundamental in understanding the Earth-Sun relationship and the cycle of seasons.