The antipodal position of a place located at 35Рsouth and 80Рwest is :

1. Earth's Grid System: Parallels of Latitude (basic)

To navigate our vast planet, geographers developed an imaginary grid system. The horizontal lines in this grid are known as Parallels of Latitude. Think of latitude as the angular distance of a place north or south of the Earth's center, measured from the Equator Physical Geography by PMF IAS, Latitudes and Longitudes, p.250. Because these lines run east-west and stay at a constant distance from one another, they never meet—hence the term "parallels."

The Equator (0°) is the most significant parallel; it is the only "Great Circle" among the latitudes, dividing the Earth into the Northern and Southern Hemispheres Exploring Society: India and Beyond, Locating Places on the Earth, p.14. A crucial physical characteristic to remember is that while all longitudes are the same length, latitudes vary in size. The circles are largest at the Equator and gradually shrink as they move toward the poles, eventually becoming mere points at 90°N and 90°S Exploring Society: India and Beyond, Locating Places on the Earth, p.14.

Beyond the Equator and the Poles, there are four special parallels that define Earth's climate zones and solar patterns:

Parallel Name	Degree	Hemisphere
Tropic of Cancer	23½° N	Northern
Tropic of Capricorn	23½° S	Southern
Arctic Circle	66½° N	Northern
Antarctic Circle	66½° S	Southern

Sources: Physical Geography by PMF IAS, Latitudes and Longitudes, p.240, 250; Exploring Society: India and Beyond (NCERT Class VI), Locating Places on the Earth, p.14, 16

2. Meridians of Longitude and the Prime Meridian (basic)

While latitudes tell us how far North or South we are, they don't give the full picture. To pinpoint a location exactly, we need a vertical reference. This is where Meridians of Longitude come in. Unlike latitudes, which are full circles of varying sizes, meridians are semi-circles of equal length that run from the North Pole to the South Pole, crossing the Equator at right angles. Physical Geography by PMF IAS, Latitudes and Longitudes, p.242. Because they all meet at the poles, the distance between any two meridians is greatest at the Equator and decreases to zero as you move toward the poles.

To measure these lines, the world needed a starting point—a "zero" line. In 1884, it was internationally agreed to use the meridian passing through the Royal Astronomical Observatory at Greenwich (near London) as the Prime Meridian. This line is designated as 0° longitude. From this point, we measure 180° Eastward and 180° Westward until they meet at the 180° line on the opposite side of the globe. Physical Geography by PMF IAS, Latitudes and Longitudes, p.242. It is fascinating to note that India had its own Prime Meridian centuries before Europe! Known as the Madhya Rekhā (middle line), it passed through Ujjayinī (modern-day Ujjain), a great center for astronomy where scholars like Varāhamihira worked nearly 1,500 years ago. Exploring Society: India and Beyond, Locating Places on the Earth, p.17.

Understanding these lines is crucial because longitude is the basis for calculating time. Since the Earth rotates 360° in 24 hours, every 15° of longitude represents one hour of time difference. To maintain administrative ease, countries choose a Standard Meridian, usually in multiples of 7°30', so that the time difference from Greenwich is in multiples of half-hours. India, for instance, uses 82°30' E as its Standard Meridian, making Indian Standard Time (IST) exactly 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT). INDIA PHYSICAL ENVIRONMENT, India — Location, p.2.

Feature	Latitudes (Parallels)	Longitudes (Meridians)
Shape	Full circles	Semi-circles
Length	Varies (Shortens toward poles)	Equal length for all meridians
Relationship	Parallel to each other	Converge at the poles

Sources: Physical Geography by PMF IAS, Latitudes and Longitudes, p.242; Exploring Society: India and Beyond, Locating Places on the Earth, p.17; INDIA PHYSICAL ENVIRONMENT, India — Location, p.2

3. Longitude and Time Zone Calculations (intermediate)

To understand how we calculate time across the globe, we must first look at the Earth's rotation. Our planet completes one full rotation of 360° in approximately 24 hours. If we break this down mathematically, the Earth rotates through 15° every hour (360 ÷ 24), or more precisely, 1° every 4 minutes Exploring Society: India and Beyond, Locating Places on the Earth, p.20. This relationship is the 'golden rule' for all longitudinal calculations. Because the Earth rotates from West to East, places located to the East see the sun earlier and are 'ahead' in time, while places to the West see the sun later and are 'behind' GC Leong, The Earth's Crust, p.11.

When calculating the time difference between two points, we follow a simple two-step process. First, determine the longitudinal difference in degrees. Second, convert those degrees into time using the 15°/hour or 4 min/degree ratio. For instance, if it is Noon (12:00 PM) at the Prime Meridian (0°) and you want to find the time at 60°E, you calculate 60 ÷ 15 = 4 hours. Since it is East, you add those hours to the base time, making it 4:00 PM GC Leong, The Earth's Crust, p.12.

A fascinating extension of this logic is the concept of Antipodal positions—points diametrically opposite to each other on the Earth's surface. To find the antipode of any location, we apply two specific shifts:

• Latitude: Keep the numerical value the same but switch the hemisphere (e.g., 35° South becomes 35° North).
• Longitude: Subtract the original longitude from 180° and reverse the direction. For example, the antipode of 80° West would be 100° East (180 - 80 = 100).

Because antipodal points are always 180° apart, they are exactly 12 hours apart in local time, representing the maximum possible time difference on Earth.

Sources: Exploring Society: India and Beyond, NCERT Class VI, Locating Places on the Earth, p.20; Certificate Physical and Human Geography, GC Leong, The Earth's Crust, p.11-12

4. International Date Line (IDL) and Great Circles (intermediate)

To understand the world map, we must first grasp the concept of Great Circles. A Great Circle is any circle that circumnavigates the Earth and passes through its center, dividing the planet into two equal hemispheres. While the Equator is the only latitude that is a Great Circle, every pair of opposite meridians (longitudes) forms a Great Circle. The most famous example is the circle formed by the Prime Meridian (0°) and the International Date Line (IDL, 180°) NCERT Class VI: Exploring Society, Locating Places on the Earth, p.24. Because these lines represent the 'shortest distance' between any two points on a sphere, pilots and navigators use 'Great Circle routes' to save fuel and time.

The International Date Line (IDL) is situated approximately at the 180° meridian, diametrically opposite the Prime Meridian. It serves as the official boundary where the calendar date changes. Because the Earth rotates from West to East, time 'gains' as you travel East from Greenwich and 'loses' as you travel West. By the time you reach the 180° meridian from both directions, there is a total time difference of 24 hours GC Leong: Certificate Physical and Human Geography, The Earth's Crust, p.14. This creates a unique rule for travelers:

• Crossing Westbound (towards Asia/Australia): You add a day to the calendar (e.g., Monday becomes Tuesday). Effectively, you "lose" a day of your life.
• Crossing Eastbound (towards the Americas): You subtract a day from the calendar (e.g., Monday becomes Sunday). You effectively "gain" or repeat a day NCERT Class VI: Exploring Society, Locating Places on the Earth, p.23.

Interestingly, the IDL is not a straight line. It zig-zags through the Pacific Ocean to ensure that island groups (like Kiribati, Tonga, or the Aleutian Islands) are not split into two different days, which would cause immense administrative chaos PMF IAS: Physical Geography, Latitudes and Longitudes, p.246.

Finally, we can find the exact opposite point of any location on Earth, known as its Antipode. To calculate an antipode, you follow two simple steps: first, keep the latitude numerical value the same but switch the hemisphere (e.g., 20°N becomes 20°S). Second, find the 180° complement for the longitude and switch the direction (e.g., 70°W becomes 110°E, because 180 - 70 = 110). These two points are always separated by a Great Circle path passing through the Earth's center.

Sources: Exploring Society: India and Beyond. Social Science-Class VI. NCERT (Revised ed 2025), Locating Places on the Earth, p.23, 24; Certificate Physical and Human Geography, GC Leong (Oxford University press 3rd ed.), The Earth's Crust, p.14; Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.), Latitudes and Longitudes, p.246

5. Earth's Geometric Properties: Diameter and Center (intermediate)

To understand geographical coordinates, we must first look at the Earth not as a perfect marble, but as a dynamic, slightly 'squashed' sphere known as a Geoid or oblate spheroid. Because the Earth rotates on its axis, it generates a centrifugal force that is strongest at the equator and zero at the poles. This force has physically 'pushed' the Earth’s mass outward, creating an equatorial bulge and a flattening at the poles Physical Geography by PMF IAS, Latitudes and Longitudes, p.241. Consequently, the Earth's diameter is not uniform; the equatorial diameter is about 43 kilometers longer than the polar diameter. This geometric quirk means you are actually closer to the Earth's center when standing at the North Pole than when standing on the Equator, which explains why gravitational force is slightly stronger at the poles Physical Geography by PMF IAS, Latitudes and Longitudes, p.241.

When we talk about the 'center' of the Earth in geography, we often use the concept of an antipode. An antipode is the point on the Earth's surface that is diametrically opposite to your current location. To find an antipode, imagine a straight line passing directly through the Earth's center. This mathematical relationship follows two strict rules:

• Latitude Rule: The numerical value stays the same, but the hemisphere flips. For example, the antipode of 20° North is 20° South.
• Longitude Rule: You subtract your current longitude from 180° and reverse the direction. If you are at 70° West, your antipode is at 110° East (180 - 70 = 110).

Visualizing these properties helps us move beyond flat maps. As noted in basic geography, trying to represent this curved, bulging surface on a flat sheet of paper is like trying to flatten an orange peel—it inevitably leads to distortion Exploring Society: India and Beyond. Social Science-Class VI, Locating Places on the Earth, p.12. Understanding the Earth's true geometry is the 'anchor' for all coordinate math.

Sources: Physical Geography by PMF IAS, Latitudes and Longitudes, p.241; Exploring Society: India and Beyond. Social Science-Class VI, Locating Places on the Earth, p.12

6. Defining Antipodes: Diametrically Opposite Points (intermediate)

In our journey through Earth's coordinates, we arrive at a fascinating geometric concept: the antipode. Derived from the Greek words anti (opposite) and pous (foot), an antipode is the point on the Earth's surface that is diametrically opposite to your current location. If you were to drill a straight line from where you are standing, passing exactly through the Earth's center, you would emerge at your antipode.

A classic example of an antipodal relationship is the Earth's rotational axis. This imaginary line connects the North Pole and the South Pole by passing through the center, making the geographic poles perfect antipodes of one another Physical Geography by PMF IAS, The Motions of The Earth and Their Effects, p.251. Interestingly, while the geographic poles are perfect opposites, the Earth's Magnetic Poles are not strictly antipodal because the magnetic field is not perfectly symmetrical Physical Geography by PMF IAS, Earths Magnetic Field (Geomagnetic Field), p.72.

To find the coordinates of an antipode, you don't need a drill; you just need two simple mathematical rules:

Coordinate	Rule for Antipode	Example (30°N, 45°W)
Latitude	Keep the number same; switch the hemisphere (N ↔ S).	30°S
Longitude	Subtract the original value from 180°; switch the direction (E ↔ W).	180 - 45 = 135°E

Essentially, the two points must be separated by 180° of longitude. Because the Earth is mostly covered by water, most land masses actually have their antipodes in the ocean. For instance, while we use coordinates to pinpoint cities like Sydney or London Certificate Physical and Human Geography, The Earth's Crust, p.10, finding a city that is a perfect antipode to another is a rare geographic coincidence!

Sources: Physical Geography by PMF IAS, The Motions of The Earth and Their Effects, p.251; Physical Geography by PMF IAS, Earths Magnetic Field (Geomagnetic Field), p.72; Certificate Physical and Human Geography, The Earth's Crust, p.10

7. Rules for Calculating Antipodal Coordinates (exam-level)

In our journey through geographical coordinates, we now reach a fascinating concept: the Antipode. Imagine you have a knitting needle and you push it straight through the center of the Earth, starting from your current location. The point where the needle emerges on the other side is your antipodal point. Because the Earth is a sphere, every location has exactly one antipode, representing the point that is diametrically opposite to it.

To calculate these coordinates, we apply two distinct mathematical rules based on how latitudes and longitudes are structured. Remember that latitudes are measured north or south of the Equator (0°), while longitudes are measured east or west of the Prime Meridian (0°) Physical Geography by PMF IAS, Latitudes and Longitudes, p.250. Because the antipode must be directly across the Earth's center, the logic follows a specific symmetry:

• Rule for Latitude: The numerical value remains exactly the same, but the hemisphere is reversed. If you are in the Northern Hemisphere, your antipode is in the Southern Hemisphere at the same distance from the Equator.
• Rule for Longitude: To find the opposite side of a 360° sphere, you must travel 180°. Therefore, you subtract your current longitude from 180° and reverse the direction (East becomes West, and West becomes East).

Let’s look at a practical calculation for a point at 25° N and 40° W:

Coordinate	Original Point	Calculation Rule	Antipodal Result
Latitude	25° N	Same number, flip N to S	25° S
Longitude	40° W	180° - 40° = 140°; flip W to E	140° E

It is important to note that while all meridians of longitude are equal in length, they converge at the poles Certificate Physical and Human Geography, The Earth's Crust, p.11. This convergence is why the calculation for the antipode of the North Pole (90° N) is simply the South Pole (90° S); at the poles, all longitudes meet, so the longitudinal difference is inherently satisfied.

Sources: Physical Geography by PMF IAS, Latitudes and Longitudes, p.250; Certificate Physical and Human Geography, The Earth's Crust, p.11

8. Solving the Original PYQ (exam-level)

Now that you have mastered the building blocks of geographic coordinates and the geometry of the globe, this question brings those concepts together perfectly. To identify an antipodal position—the point diametrically opposite to any location on Earth—you must apply two specific transformations. As you learned in the conceptual phase, an antipode requires a hemispheric flip for latitude and a 180-degree shift for longitude, ensuring the line between the two points passes directly through the Earth's center, as noted in Wikipedia: Antipodes.

Let’s walk through the reasoning as if we were in the exam hall. First, address the latitude: if the original point is at 35° South, its mirror image must be at the same numerical distance from the Equator but in the opposite hemisphere—hence, 35° North. Second, calculate the longitude: because the Earth is a 360° sphere, the opposite meridian is 180° away. You subtract the given 80° West from 180° (180 - 80 = 100) and switch the direction to East. By combining these two steps, we arrive at the correct answer: (B) 35° North and 100° East.

UPSC often includes distractors to test your precision under pressure. Options (A) and (D) use 55°, which is a common mathematical trap designed for students who mistakenly calculate the complementary angle (90 minus 35) instead of keeping the latitude value constant. Option (C) is a conceptual trap; since latitude only ranges from 0° to 90°, a coordinate of 100° North is geographically impossible. Recognizing these patterns ensures you don't just calculate the answer, but you also verify it against the logical constraints of the Earth's grid.