Globe: Latitudes and Longitudes

Latitude: The angular distance of a point north or south of the Equator, measured in degrees (°) from 0° (Equator) to 90° (Poles).

Parallels: Lines of latitude are called parallels because they run parallel to each other, never meeting. Unlike meridians, they are not equal in length — the Equator is the longest (circumference ~40,075 km), and parallels get shorter toward the poles.

Equator: The most important parallel — divides Earth into Northern and Southern Hemispheres; marks where the Sun is directly overhead at the equinoxes (March 21 and September 23).

Longitude: The angular distance of a point east or west of the Prime Meridian, measured in degrees from 0° to 180° East or West.

Meridians: Lines of longitude are called meridians. Unlike parallels, all meridians are the same length (semicircles from pole to pole); they all converge at the poles.

Prime Meridian (Greenwich Meridian, 0°): Passes through the Royal Observatory, Greenwich, London. Established by international agreement in 1884. Divides East and West hemispheres.

The connection between longitude and time:

The Earth rotates 360° in 24 hours → 15° per hour → 1° every 4 minutes.

As you move east, time is ahead (the Sun rises earlier). As you move west, time is behind.

India's Standard Time (IST):

• India's east-west extent is ~30° (from ~68°E to ~97°E)
• A single time zone is used: IST = UTC + 5:30
• Standard Meridian: 82°30'E — passes through Mirzapur (UP), close to the geographical centre of India
• This means there's up to 2 hours difference in actual sunrise time between Gujarat (west) and Arunachal Pradesh (east)

Why not multiple time zones? India chose a single time zone for national unity and administrative simplicity. However, states like Assam and northeastern states face issues — it stays light late and dark early. There have been proposals for a separate "Chaibagaan (Tea Garden) Time" for the Northeast (+1 hour from IST).

International Date Line (IDL): Roughly follows the 180° meridian, but with deviations to avoid cutting through countries and island groups. It runs through the Pacific Ocean.

Crossing the IDL:

• Traveling eastward across the IDL → subtract one day
• Traveling westward across the IDL → add one day

This ensures that different parts of the world don't have different dates just because of their position. Without the IDL, someone circumnavigating the Earth would gain or lose a day (Jules Verne's Around the World in 80 Days famously uses this plot device).

The IDL is not a straight line — it deviates to ensure that all of Russia, all of Alaska, and all of Kiribati remain on one side (so countries aren't split between two dates).