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Take a look at the essential events, concepts, terms, quotes, or phenomena every day and brush up your knowledge. Here’s your knowledge nugget for today.
(Relevance: The concepts of Uttarayan, equinox, and solstice hold great importance for the UPSC CSE, as these are not only significant geographical phenomena, but UPSC has previously asked questions about them.)
Uttarayan, the six months between Makar Sankranti and Karka Sankranti, marks the Sun’s northward movement (as observed from Earth) in the celestial sphere.
1. Considered one of the most ancient Hindu festivals, Uttarayan celebrated in north India as Makar Sankranti, is dedicated to the sun god. This festival marks the arrival of the harvest season and the end of winter. It is also associated with different traditions like flying kites and taking holy dip in rivers.
2. Astronomical Context: In addition to its cultural significance, Uttarayan also represents an important geographical phenomenon. As we all know, the duration of sunlight in a day varies throughout the year. Longer hours of sunlight are associated with the summer season, while shorter periods of sunlight occur during the winter. Additionally, the position of sunrise changes daily; it drifts northward, then southward, and back north, completing one cycle over the course of a year. In our region, the southward shift in the position of sunrise indicated the approach of winter, whereas the northward shift signalled the onset of summer.
| Why are the hours of daylight not the same every day? |
| The Earth’s axis of rotation is tilted at an angle of 23.5° to its orbital plane. This tilt — combined with factors such as Earth’s spin and orbit — leads to variations in the duration of sunlight that any location on the planet receives on different days of the year. |
3. When the Sun begins its northward journey after reaching its southernmost point, it is said to enter Uttarayan. Conversely, when the Sun started travelling southward from its northernmost position, it is said to enter Daksinayana.
1. June 21 is the longest day of the year for anyone living north of the Equator. This day is referred to as the summer solstice, and it occurs when the Sun is directly over the Tropic of Cancer, or more specifically, right over 23.5 degrees north latitude.
2. Since Earth rotates on its axis, the Northern Hemisphere gets more direct sunlight between March and September over the course of a day, which also means people living in the Northern Hemisphere experience summer during this time. The rest of the year, the Southern Hemisphere gets more sunlight.
3. During the solstice, the Earth’s axis — around which the planet spins, completing one turn each day — is tilted in a way that the North Pole is tipped towards the Sun and the South Pole is away from it.
4. Typically, this imaginary axis passes right through the middle of the Earth from top to bottom and is always tilted at 23.5 degrees with respect to the Sun. Therefore, the solstice, as NASA puts it, is that instant in time when the North Pole points more directly toward the Sun than at any other time during the year.
5. This day, the Earth receives a greater amount of energy from the Sun. The maximum amount of sunlight received by the Northern Hemisphere during this time is usually on June 20, 21, or 22. In contrast, the Southern Hemisphere receives most sunlight on December 21, 22, or 23 when the Northern Hemisphere has its longest nights — or the winter solstice.
6. Notably, the amount of light received by a specific area in the Northern Hemisphere during the summer solstice depends on the latitudinal location of the place. The further north one moves from the equator, the more light one receives during the summer solstice. At the Arctic Circle, the sun does not set during the solstice.
Winter Solstice, December 21, is the day when the North Pole is most tilted away from the Sun. In the Northern Hemisphere, it occurs when the sun is directly over the Tropic of Capricorn, which is located at 23.5° south of the equator and runs through Australia, Chile, southern Brazil, and northern South Africa.
1. When the Earth’s axis is tilted neither toward nor away from the sun that time is known as Equinoxes. During the Equinoxes, there is a “nearly” equal amount of daylight and darkness at all latitudes.
2. According to the NOAA website- The “nearly” equal hours of day and night are due to refraction of sunlight or a bending of the light’s rays that causes the sun to appear above the horizon when the actual position of the sun is below the horizon.
3. Additionally, the days become a little longer at the higher latitudes (those at a distance from the equator) because it takes the sun longer to rise and set. Therefore, on the equinox and for several days before and after the equinox, the length of day will range from about 12 hours and six and one-half minutes at the equator, to 12 hours and 8 minutes at 30 degrees latitude, to 12 hours and 16 minutes at 60 degrees latitude.
(Sources: Happy Uttarayan, ncert.nic.in, What is summer solstice?)
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