On which of the following day does the summer solstice occurs in the southern hemisphere ?

Question

UnlockIAS · Accepted Answer

Correct — option (4), '22 December'. The single word that decides this question is 'southern'. The Earth's axis is inclined at about 23.5 degrees to the perpendicular of its orbital plane and holds that direction fixed as the Earth travels round the Sun, so as the year passes, first one hemisphere and then the other is tilted towards the Sun. A solstice is the moment at which that tilt reaches its extreme, and it is marked by the Sun's vertical rays falling on a tropic rather than on the equator. On about 22 December the Sun is directly overhead at the Tropic of Capricorn, at 23.5 degrees south. The southern hemisphere is then turned towards the Sun: it receives the year's most direct radiation, its day is the longest and its night the shortest of the year, the whole area within the Antarctic Circle has continuous daylight, and the season there is summer. That is the summer solstice of the southern hemisphere, and option (4) is the answer. The same date is simultaneously the winter solstice of the northern hemisphere — the shortest day in India — which is exactly why the question is worth asking and exactly how it is failed. Indian textbooks, written for the northern hemisphere, usually give 21 June as 'the summer solstice' without qualification, and a candidate who has stored the phrase without the hemisphere attached will read the stem, recognise the words 'summer solstice' and mark 21 June. The two solstice dates and the two equinox dates are not four separate facts about the Earth; they are two positions in the orbit, each of which carries opposite names in the two hemispheres. Once that is grasped, the question becomes a matter of naming the position rather than recalling a date: maximum southern tilt means the Sun over Capricorn, which means late December. It is worth noting that these dates shift by a day either way through the leap-year cycle, so the solstice may fall on 21 or 22 December; the paper uses the conventional textbook date.

Why the other options are wrong — (a) 21 March is an equinox, not a solstice, so it is disqualified before hemispheres are even considered. On that date the Sun's vertical rays fall on the equator, neither hemisphere is tilted towards it, and day and night are of nearly equal length everywhere on the Earth — which is what the word equinox means. It is called the spring or vernal equinox in the northern hemisphere and the autumnal equinox in the southern, so it too carries opposite names on either side of the equator, but no equinox is a solstice under any name. A candidate who chooses it has generally kept the four dates as an undifferentiated list without recording which two are the extremes of tilt and which two are the moments of balance between them.  (b) This is the trap the question is built around, and it is the wrong answer that costs the most marks. 21 June is indeed a solstice, and in the northern hemisphere it is the summer solstice: the Sun stands overhead at the Tropic of Cancer, India has its longest day, and the region within the Arctic Circle has continuous daylight. But on that same date the southern hemisphere is tilted away from the Sun, so it is having its shortest day and its winter solstice. The stem asks specifically about the southern hemisphere, and the answer therefore has to be the opposite solstice. This option catches anyone who has memorised 'summer solstice — 21 June' as a fixed pair, which is how the fact is usually printed in books written for readers in the north, and who then reads past the word 'southern' in a stem whose grammar is already awkward.  (c) 23 September is the second of the two equinoxes, when the Sun's vertical rays again fall on the equator and day and night are nearly equal everywhere. In the northern hemisphere it is called the autumnal equinox and in the southern the spring equinox — the mirror of 21 March. Like the March date it is a moment of balance rather than of extreme tilt, so it cannot be a solstice for either hemisphere. Choosing it usually means the candidate has correctly reasoned that the answer must be a date associated with the southern hemisphere's warming season and has then picked the September date because spring in the south begins around then. Spring is not summer, and an equinox is not a solstice; the stem asks for the extreme, which comes three months later.

Concept: The seasons are produced by two facts working together: the Earth revolves round the Sun in a year, and its axis is tilted about 23.5 degrees from the perpendicular to the plane of that orbit while remaining parallel to itself throughout the journey. Because the tilt does not swing to follow the Sun, the hemisphere leaning towards it changes continuously through the year, and with it the angle at which sunlight strikes the ground and the number of hours of daylight. Four positions in the orbit are given names. At the two solstices the tilt is at its maximum: on about 21 June the Sun is overhead at the Tropic of Cancer and on about 22 December at the Tropic of Capricorn, which is why the tropics lie where they do — they are the extreme limits of the Sun's apparent annual migration. At the two equinoxes, about 21 March and 23 September, the Sun is overhead at the equator, the circle of illumination passes through both poles, and day and night are of nearly equal length everywhere. The polar circles at 66.5 degrees follow from the same tilt, being the latitudes beyond which the Sun fails to set at one solstice and fails to rise at the other. It is worth destroying one persistent misconception here: the Earth is actually nearest the Sun in early January and farthest in early July, so distance plainly cannot be what makes January cold in Maharashtra. The tilt does all the work.

State PCS 2023 Q27 — Geography PYQ with Answer

State PCS 2023 Q27 — Geography PYQ with Answer