In basic astronomy and geography, on which date is the longest day generally observed in the Northern Hemisphere, giving the maximum duration of daylight?

Introduction / Context:
This question complements the one about the shortest day and focuses on the summer solstice in the Northern Hemisphere. Due to the tilt of the Earth axis, different latitudes receive varying amounts of sunlight through the year. The summer solstice marks the day with the longest period of daylight and shortest night in the Northern Hemisphere. School geography and many general knowledge books state that this occurs around 21 June. Remembering this date is important for answering astronomy related questions that frequently appear in competitive examinations.

Given Data / Assumptions:

• The region of interest is the Northern Hemisphere, which includes India.
• The question asks for the date of the longest day of the year.
• Options are December 22, June 21, August 21 and September 22.
• We assume the commonly taught approximate date used in Indian school textbooks.

Concept / Approach:
The Earth orbits the Sun with its axis tilted about 23.5 degrees. When the Northern Hemisphere is tilted towards the Sun, it experiences summer, and the day with the greatest tilt towards the Sun yields the maximum duration of daylight. This is called the summer solstice. It falls around 21 June. Standard school level explanations pair this with 22 December as the shortest day in the Northern Hemisphere. Therefore, the correct answer in most exam oriented contexts is 21 June, as reflected in the option June 21.

Step-by-Step Solution:
Step 1: Interpret longest day as referring to the summer solstice for the Northern Hemisphere. Step 2: Recall that summer in the Northern Hemisphere occurs around June and July, not December or September. Step 3: Eliminate December 22, which is associated with the winter solstice and shortest day, and September 22, which is close to an equinox where day and night are nearly equal. Step 4: Recognise that August 21 is in late summer but is not the solstice date mentioned in textbooks. Step 5: Select June 21 as the standard date for the longest day in the Northern Hemisphere.

Verification / Alternative check:
One easy check is to remember the solstice pair: June 21 for longest day and December 22 for shortest day in the Northern Hemisphere, as presented in many Indian school books. If a learner memorises this pair, then when asked about longest day, June 21 immediately comes to mind, and when asked about shortest day, December 22 appears as the familiar value. The equinoxes around March 21 and September 22 give nearly equal day and night and thus can be excluded for questions on extreme lengths of day and night.

Why Other Options Are Wrong:
December 22 is linked with the winter solstice and corresponds to the shortest day, not the longest day, in the Northern Hemisphere. August 21 is part of the summer period but is not the precise solstice date; by then the day length has already started to decrease slowly from the maximum reached in June. September 22 is near the autumn equinox when day and night are roughly equal in length, so it does not represent the longest day.

Common Pitfalls:
Candidates often confuse solstices and equinoxes or mix up which dates correspond to maximum and minimum day lengths. Another common mistake is to remember that June is related to long days but fail to recall the specific date, leading to guesses if similar numbers appear in options. To avoid such problems, aspirants should memorise the four key dates associated with solstices and equinoxes and understand the physical meaning of each, then link June 21 clearly with longest day in the Northern Hemisphere.

Final Answer:
The longest day of the year in the Northern Hemisphere, with maximum daylight duration, is generally observed on June 21.