At noon on these two equinoxes, the sun is directly above at the equator. The "almost" equal hours of day and night are caused by sunlight refraction or bending of the light's beams, which allows the sun to seem above the horizon while its real location is below the horizon. At high latitudes where the sun is lower in the sky during midday, these periods of equal darkness last for less than an hour.
At the equator, daytime and nighttime are equal length. The sun rises and sets exactly at mid-morning and mid-afternoon regardless of the date or time of year. The period between sunrise and sunset is called daylight, dawn and dusk all mean the same thing here. Night falls as soon as the sun has set, there is no twilight at the equator.
At higher latitudes, daytime is longer than nighttime. The difference becomes more pronounced at higher altitudes, where there is less atmosphere to refract and bend light rays from the sun. Here on Earth, the line on which daytime and nighttime are equal divides the planet into a band that stretches around the globe about halfway between the poles and reaches from the northernmost to the southernmost points on Earth. This region is known as the tropics.
At the equator, the line on which days and nights are equal passes through the center of Earth.
The tilt of the Earth's axis is perpendicular to the sun's beams on the equinox, as seen in the figure. The sun will be visible for 24 hours at the South Pole. A fantastic opportunity to witness the Midnight Sun! All year round, the day on the equator is little longer than 12 hours. Sunrise and sunset occur simultaneously, around 6 a.m. and 6 p.m., respectively.
At the North Pole, the sun is below the horizon for 3 months out of the year. At the South Pole, it is above the horizon for 3 months out of the year.
These are just two examples. The tilt of the Earth's axis can be anything from 0 to 90 degrees; a zero-degree axis makes the days and nights equal in length, while a 90-degree axis makes one day equal to two years of ordinary time.
You might have heard that at the poles, the sun rises and sets at midnight? This is not true - at the poles, the sun never goes down. It is just hidden behind the earth's shadow.
In fact, around the world except at the poles, the sun will rise every morning about an hour after sunrise and set every evening about an hour before sunset. The length of daylight changes throughout the year at different rates depending on where you are on Earth, but on average, there is sunlight for 14 hours per day in summer and 2 hours in winter.
At latitudes where the Sun is directly above the Earth's equator (on the equinoxes of approximately March 20 and September 23), sunlight shines perpendicular to the Earth's axis of rotation, and all latitudes have a 12-hour day and 12-hour night. At other times of the year, solar radiation does not come straight down but instead is scattered by clouds and aerosols in the atmosphere.
The phrase "equatorial region" is used to describe any region on or near the equator, including both the tropics and the higher latitude continents. The term refers to the fact that the axis of Earth is tilted at an angle with respect to the orbit of Mars, so that the Sun appears to rise about 6 degrees north of east at the North Pole and to set about 6 degrees south of west at the South Pole. This is why people living at high northern and southern latitudes experience seasons: winter at the poles and summer at the equator. But the tilt of the Earth's axis is not constant; it changes over time due to gravitational forces acting on the planet's core. As a result, the length of each season varies from year to year and from place to place on Earth.
In addition to the change in length of the days and nights, the location of the Earth's center of mass also affects how much energy is received at different locations on its surface.
Regardless of the season, the sun rises and sets perpendicularly from the horizon at the equator. This effect causes the dawn to appear three minutes sooner and the sunset to appear three minutes later. At the poles, however, where there is no shadow at midday, the sun never sets or rises. Instead, it remains continuously over the pole during the year.
At the equator, the angle between the ground and the sky is zero degrees (90 degrees for a plane), so the rise and set of the sun is exactly parallel to the earth's surface.
The only time when the sun is not rising or setting at the equator is around the new and full moons. At these times, it is neither going up nor down.
The equatorial region includes most countries in Africa and South America. The only exceptions are North Korea and part of Siberia Russia that lie outside the tropics but still near them. These areas experience tropical climates, except during the coldest months of January and February when the sun doesn't rise at all.
In fact, if you travel to either of these regions, you'll notice that the sun seems to disappear altogether for a few hours each day. During this time, it is completely hidden by clouds or darkness.
The vernal equinox On the first day of spring (vernal equinox) and the first day of fall, the sun is directly above at noon on the equator (autumnal equinox). As you move away from the equator, it takes longer for the sun to reach its highest point in the sky. At the poles, where it doesn't rise at all, the vernal equinox doesn't occur.
At other times of the year, when the Earth is not at the same angle as the Sun, there will be local conditions that cause different parts of the planet to experience either spring or autumn. For example, in the southern hemisphere, where we would call summer, the sun rises about 65 degrees east of south, which means that at mid-summer it is still winter over much of Australia. South of 35 degrees east longitude, the sun never reaches 13th heaven; instead, it sets every night around midnight. The reason is that at those latitudes the atmosphere is very thick with clouds most of the time, so no part of Australia ever sees direct sunlight for more than a few hours each day.
In northern Canada, where we would call winter, the reverse is true: the sun reaches its highest point in the sky at midday, even though it is in the middle of summer.