Understanding Sunrise Time Difference in India

The Earth rotates from west to east. This rotation causes different longitudes to experience sunrise at different times. As the sun appears to move across the sky from east to west, places located further east experience sunrise earlier than places located further west.

Factors Affecting Sunrise Time

• Longitude: This is the primary factor causing time differences across different places on Earth. Each degree of longitude corresponds to a specific time difference.
• Earth's Rotation: The Earth completes one full rotation (\(360^\circ\)) in approximately 24 hours.

Calculating Time Difference Based on Longitude

The relationship between longitude and time is crucial for understanding local time differences. Here's how it works:

• In 24 hours, Earth rotates \(360^\circ\).
• In 1 hour (\(60\) minutes), Earth rotates \(\frac{360}{24} = 15^\circ\).
• In 1 minute, Earth rotates \(\frac{15}{60} = \frac{1}{4}^\circ\).
• Conversely, for every \(1^\circ\) of longitude difference, the time difference is \(4\) minutes \(\left(1^\circ \text{ longitude} \times \frac{60 \text{ minutes}}{15^\circ \text{ longitude}}\right)\).

Longitudinal Extent of India

India spans a vast longitudinal extent, from approximately \(68^\circ7'\) East longitude in the west to \(97^\circ25'\) East longitude in the east.

• The westernmost point of mainland India is in Gujarat.
• The easternmost point of mainland India is in Arunachal Pradesh.

Estimating the Time Difference Between Arunachal Pradesh and Gujarat

To find the approximate time difference in sunrise between eastern Arunachal Pradesh and western Gujarat, we need to consider their approximate longitudinal difference.

• Approximate longitude of eastern Arunachal Pradesh: \(97^\circ\) E
• Approximate longitude of western Gujarat: \(68^\circ\) E
• Longitudinal difference = \(97^\circ \text{ E} - 68^\circ \text{ E} = 29^\circ\)

Now, we convert this longitudinal difference into a time difference:

Time difference = Longitudinal difference \(\times\) Time per degree longitude

Time difference = \(29^\circ \times 4\) minutes/degree

Time difference = \(116\) minutes

\(116\) minutes is very close to \(2\) hours (\(120\) minutes).

Since Arunachal Pradesh is in the east, the sunrise occurs approximately 2 hours earlier there than in western Gujarat.

Revision Table: Key Concepts

Additional Information: Standard Time in India

Despite the significant time difference of about 2 hours between the eastern and western parts of India, the country follows a single Indian Standard Time (IST). IST is based on the longitude of \(82^\circ30'\) E, which passes near Mirzapur in Uttar Pradesh.

• Having a single time zone simplifies coordination for various activities like transport, communication, and administration across the country.
• However, this means that local time varies significantly from IST in the extreme eastern and western regions, leading to earlier sunrises and sunsets in the east and later ones in the west compared to the standard clock time.