<P> All phases of dawn and dusk are shortest at the equator, where the Sun at equinox rises and sets at a right angle to the horizon; the steps between civil, nautical, and astronomical dawn or dusk correspond to only 24 minutes each . At all places on the earth, dawn and dusk times are fastest around the equinoxes and slowest at the summer and winter solstices . </P> <P> As the calendar approaches the summer or winter solstice, the days or nights, respectively, get longer, which can have a potential impact on the time and duration of dawn and dusk . This effect is more pronounced closer to the poles, where the Sun rises at the spring equinox and sets at the autumn equinox, with a long period of dawn / dusk, lasting for a few weeks . </P> <P> The polar circle (at 66 ° 34 ′ N or S) is defined as the lowest latitude at which the Sun does not set at the summer solstice . Therefore, the angular radius of the polar circle is equal to the angle between the plane of Earth's equator and that of the ecliptic . This period of time with no sunset lengthens closer to the pole . </P> <P> Near the summer solstice, latitudes higher than 54 ° 34 ′ get no darker than nautical dawn / dusk; the "darkness of the night" varies greatly in these latitudes . </P>

When does the sky start to get light