Are the length of daylight and night equal at the equinoxes?

Question and answer submitted by Kent Ellis, Physics Teacher, Flagstaff High School, Flagstaff, AZ.

Equinox is from the Latin for ‘equal night’, and indicates the time when daylight and darkness are equal. This occurs because the sun is at a right angle to Earth’s axis, and the northern and southern hemispheres get the same exposure to the sun. This suggests that daytime and darkness are of equal duration at the equinoxes.

However, we get some bonus sunlight because the Earth’s atmosphere refracts the sunlight, bending it a small amount around the nighttime side. The causes sunrise to be little earlier than it would be otherwise, and sunset to be a little later. So at the exact time of the equinoxes the days are longer than the nights for both hemispheres.

The days of 12-hours of daylight and 12-hours of darkness occur about five days after the autumnal equinox and five days before the vernal equinox.

In the diagram sunlight is coming from the left, lighting the left half of the Earth. The sunlight is refracted as it hits the Earth’s atmosphere. The equator line points to the sun, because at the time of the equinoxes the sun is in the plane of the equator. The diagram exaggerates the depth of the atmosphere, the amount of refraction, and the size of the ‘extra’ daylight region.

Answer extended by Joe Portney of Navsense:

Another factor that increases the length of daylight is that the sun is a large object, and it takes time for it to rise and set completely. Daylight starts as soon as we see the top edge of the sun above the horizon, giving us a little extra compared to what we would see if the sun was a point source of light. A similar situation occurs at sunset. Altogether, we get extra daylight equal to the amount of time it takes the sun to rise or set completely.

In The Natural Year, the equinoxes and solstices are shown in diagrams at the appropriate locations around the year.

Are the length of daylight and night equal at the equinoxes?

Question and answer submitted by Kent Ellis, Physics Teacher, Flagstaff High School, Flagstaff, AZ.

Equinox is from the Latin for ‘equal night’, and indicates the time when daylight and darkness are equal. This occurs because the sun is at a right angle to Earth’s axis, and the northern and southern hemispheres get the same exposure to the sun. This suggests that daytime and darkness are of equal duration at the equinoxes.

However, we get some bonus sunlight because the Earth’s atmosphere refracts the sunlight, bending it a small amount around the nighttime side. The causes sunrise to be little earlier than it would be otherwise, and sunset to be a little later. So at the exact time of the equinoxes the days are longer than the nights for both hemispheres.

The days of 12-hours of daylight and 12-hours of darkness occur about five days after the autumnal equinox and five days before the vernal equinox.

In the diagram sunlight is coming from the left, lighting the left half of the Earth. The sunlight is refracted as it hits the Earth’s atmosphere. The equator line points to the sun, because at the time of the equinoxes the sun is in the plane of the equator. The diagram exaggerates the depth of the atmosphere, the amount of refraction, and the size of the ‘extra’ daylight region.

Answer extended by Joe Portney of Navsense:

Another factor that increases the length of daylight is that the sun is a large object, and it takes time for it to rise and set completely. Daylight starts as soon as we see the top edge of the sun above the horizon, giving us a little extra compared to what we would see if the sun was a point source of light. A similar situation occurs at sunset. Altogether, we get extra daylight equal to the amount of time it takes the sun to rise or set completely.

In The Natural Year, the equinoxes and solstices are shown in diagrams at the appropriate locations around the year.

Are the length of daylight and night equal at the equinoxes?

Question and answer submitted by Kent Ellis, Physics Teacher, Flagstaff High School, Flagstaff, AZ.

Equinox is from the Latin for ‘equal night’, and indicates the time when daylight and darkness are equal. This occurs because the sun is at a right angle to Earth’s axis, and the northern and southern hemispheres get the same exposure to the sun. This suggests that daytime and darkness are of equal duration at the equinoxes.

However, we get some bonus sunlight because the Earth’s atmosphere refracts the sunlight, bending it a small amount around the nighttime side. The causes sunrise to be little earlier than it would be otherwise, and sunset to be a little later. So at the exact time of the equinoxes the days are longer than the nights for both hemispheres.

The days of 12-hours of daylight and 12-hours of darkness occur about five days after the autumnal equinox and five days before the vernal equinox.

In the diagram sunlight is coming from the left, lighting the left half of the Earth. The sunlight is refracted as it hits the Earth’s atmosphere. The equator line points to the sun, because at the time of the equinoxes the sun is in the plane of the equator. The diagram exaggerates the depth of the atmosphere, the amount of refraction, and the size of the ‘extra’ daylight region.

Answer extended by Joe Portney of Navsense:

Another factor that increases the length of daylight is that the sun is a large object, and it takes time for it to rise and set completely. Daylight starts as soon as we see the top edge of the sun above the horizon, giving us a little extra compared to what we would see if the sun was a point source of light. A similar situation occurs at sunset. Altogether, we get extra daylight equal to the amount of time it takes the sun to rise or set completely.

In The Natural Year, the equinoxes and solstices are shown in diagrams at the appropriate locations around the year.