Karachi (June 21, 2018): Pakistan, as well as countries located on the Northern hemisphere of the globe, will experience the longest day of the year on Thursday (Today).
Officials of the Pakistan Meteorological Department (PMD) say that in technical parlance the phenomenon is referred to as the summer solstice.
“Solstice is defined as either of the two times of the year at which the sun is furthest south or north of the equator. The winter solstice falls on Dec 22 while the summer solstice takes place on June 21,” explains PMD officials. But the countries located on the Southern hemisphere will experience the shortest day, he adds.
From now on the day will start getting shorter by each passing day till December 21 which is the shortest day of the year.
On March 21 and Sept 22, day and night are of equal length, he says and adds that either time is known as equinox when the sun crosses the equator.
June 21 is called summer solstice. Summer solstice occurs when a planet’s rotational axis, or geographic pole on either its northern or its southern hemisphere, is most inclined toward the star that it orbits.
On the summer solstice, Earth’s maximum axial tilt toward the Sun is 23.44°. Likewise, the Sun’s declination from the celestial equator is +23.44° in the Northern Sky and −23.44° in the Southern Sky. This happens twice each year (once in each hemisphere), when the Sun reaches its highest position in the sky as seen from the north or South Pole.
December 21, as already mentioned is winter solstice. Winter solstice happens every year when the Sun reaches its most southerly declination of -23.5 degrees. In other words, when the North Pole is tilted farthest- 23.5 degrees- away from the Sun, delivering the fewest hours of sunlight of the year.
While summer solstice, which occurs on June 21, is the longest day of the year the winter solstice which occurs on December 21 is the shortest day of the year. The two days are exactly six months apart.
Besides two Solstices two Equinoxes also occurred during a year. On an equinox, day and night are of approximately equal duration all over the planet. They are not exactly equal, however, due to the angular size of the sun and atmospheric refraction. To avoid this ambiguity, the word equilux is sometimes (but rarely) used to mean a day in which the durations of light and darkness are equal.
Equinoxes are also about six months apart- on March 20 and September 23. An equinox is the moment in which the plane of Earth’s equator passes through the center of the Sun.
Related News:
