Declination is the measure of how far a celestial object is from the celestial equator, measured in degrees. It is one of the two coordinates used to locate objects in the sky, the other being right ascension.
Declination is important because it helps determine the altitude of a star in the sky from a particular location. The higher the declination, the higher the star will appear in the sky, making it easier to see.
Declination and latitude are closely related, as they both measure the distance of an object from the celestial equator. In fact, the latitude of a location is equal to the declination of objects directly overhead at that location.
The minimum declination of stars that can be seen with the naked eye depends on the location and time of year. For example, at the equator, stars with a declination of +90 degrees (directly overhead) to -90 degrees (on the horizon) can be seen throughout the year. However, at higher latitudes, the minimum declination will vary depending on the season.
No, there is no specific declination value that guarantees the visibility of stars. Other factors such as weather, light pollution, and atmospheric conditions can also affect the visibility of stars. However, generally, stars with a declination of +90 degrees to -20 degrees can be seen in most locations throughout the year.