The vernal equinox (about March 21) marks the beginning of spring by making day and night equal in length. Summer solstice (June 20 or 21): the longest day of the year, signaling the beginning of summer. Autumnal equinox (about September 23): a day and night of equal duration that marks the beginning of fall. The winter solstice (December 22) is when day becomes shortest and night lasts the longest.
The four seasons are based on events that happen with respect to the Earth's position relative to the Sun. At perihelion (the closest point to the Sun), the Earth's axis is tilted at an angle of about 5 degrees relative to the orbital plane of the Sun. At this time of year, the Northern Hemisphere is experiencing spring, when the days are getting longer and the snow is melting. Summer comes around the time of the summer solstice, when the Earth is at its most distant from the Sun and can be as much as 14 degrees north or south of the equator. The days are now longest, but it's also very hot outside because the Sun is over the horizon for 24 hours. Fall begins when the Earth returns to its orbit around the Sun, moving away from perihelion. The days are shorter and cooler than they were during spring, but not cold enough for frost at the equator. Winter occurs when the Earth is at its furthest distance from the Sun, and can be as far as 50 degrees north or south of the equator.
Summer solstice (June 20 or 21): the longest day of the year, marking the start of summer. Autumnal equinox (about September 23): a day and night of equal duration signaling the start of fall. Winter solstice (December 21 or 22): the shortest day of the year, indicating the start of winter. Spring equinox (about March 19): a day and night of equal duration signaling the start of spring.
These are the official definitions from NASA. But you can think of them as different seasons of the year based on how long it takes for the sun to go through these phases: summer, spring, winter, and autumn. They all share the same earth around which it orbits, but because they occur at different times of year, our location on this earth determines what season we are in at any given time.
For example, if you were standing in New York City in June, it would be summer there, but if you were standing in San Francisco in December, it would be cold there! The only thing that keeps us warm is the knowledge that soon enough it will be summer again...
The four seasons described above are just two of many that can be defined by looking at the relationship between the sun, earth, and moon. There are also two more seasonal periods that can be identified using astronomical observations: the rainy season and the harvest season.
SOLSTICES AND EQUINOXES
|Vernal Equinox||March 20||0°|
|Summer Solstice||June 21||23.5°N|
|Autumnal Equinox||September 23||0°|
|Winter Solstice||December 22||23.5°S|
The vernal equinox, the first day of spring, features 12 hours of sunshine and 12 hours of darkness. The name "vernal" comes from the Latin word for "spring," while the phrase "equinox" comes from the Latin word for "equal night." Because of the abundance of water, light, warmth, and soil available during the spring, many trees, flowers, plants, and bulbs begin to flourish (compost). As the summer months approach, the temperatures rise and the snow begins to melt, causing rivers, creeks, and lakes to flow again.
There are two types of springs: hot and cold. A hot spring is one that is naturally heated by an underground source of heat. The water in these springs is usually at a high temperature, which can be beneficial for bathing. However, because the water is so hot, you need to be careful not to get any of it on your skin. The temperature of a hot spring can also be harmful if you slip and fall into it! A cold spring is one that flows out of frozen ground. The water in these springs is usually very cold, so taking a bath or shower in one is fun for everyone involved!
Many people think that only natural springs are cool. This is not true; even man-made springs can be cool. If you live in a area where there is heavy traffic on the road near a pool, lake, or other body of water, then someone will most likely have turned on the fountain option for their vehicle stereo system.