Understanding Sunrise Time and Longitude

The time of sunrise at any location on Earth is primarily determined by its longitude. As the Earth rotates from west to east, places located further to the east experience sunrise earlier than places located to the west. This is because they are the first to face the rising sun.

To determine the chronological order of sunrise for the given places in India, we need to consider their relative longitudes. India's longitudinal extent is roughly between 68° East and 97° East. The easternmost parts of the country will see the sun rise much earlier than the westernmost parts.

Locating the Cities and Their Longitudes

Let's identify the approximate locations and longitudes of the four cities:

• Itanagar: Capital of Arunachal Pradesh, located in the northeastern part of India. Approximate Longitude: 93.6° E.
• Imphal: Capital of Manipur, located in the northeastern part of India. Approximate Longitude: 93.9° E.
• Agartala: Capital of Tripura, located in the northeastern part of India, but further west compared to the others. Approximate Longitude: 91.3° E.
• Aizawl: Capital of Mizoram, located in the northeastern part of India. Approximate Longitude: 92.7° E.

Comparing Longitudes for Sunrise Order

To find the chronological order of sunrise, we arrange the cities from east to west based on their longitudes. The city with the highest eastern longitude will have the earliest sunrise, and the city with the lowest eastern longitude among the given options will have the latest sunrise.

Arranging the cities from the highest longitude (earliest sunrise) to the lowest longitude (latest sunrise):

1. Imphal ($93.9^\circ$ E) - Earliest sunrise
2. Itanagar ($93.6^\circ$ E)
3. Aizawl ($92.7^\circ$ E)
4. Agartala ($91.3^\circ$ E) - Latest sunrise among these four

Determining the Chronological Order of Sunrise

Based on the east-to-west order determined by longitude, the cities will experience sunrise in the following sequence:

1. Imphal (Number 2)
2. Itanagar (Number 1)
3. Aizawl (Number 4)
4. Agartala (Number 3)

Therefore, the correct chronological order of sunrise for the given places is 2-1-4-3.

Revision Table: Sunrise Order

Additional Information on Sunrise and Time Zones

The concept of longitude and sunrise time is fundamental to understanding time zones. Although different locations on different longitudes have different local times based on the sun's position, a standard time is adopted within a region or country for convenience.

• India follows a single standard time, Indian Standard Time (IST), which is based on the longitude $82.5^\circ$ E, passing near Mirzapur in Uttar Pradesh.
• Due to India's wide longitudinal extent ($68^\circ$ E to $97^\circ$ E, a difference of about $29^\circ$), there is a significant difference between the local time based on the sun and IST, especially in the easternmost and westernmost parts.
• The difference in time for every degree of longitude is 4 minutes. So, across India's width, the time difference based purely on longitude is approximately $29 \times 4 = 116$ minutes, or close to two hours.
• This is why sunrise happens much earlier in the northeastern states like Arunachal Pradesh and Manipur compared to the western states like Gujarat, even though both follow the same IST.