The planet we live on

The planet we live on is not the biggest, but it’s the most important by far. It is amazingly well designed to support a huge variety of life.

Size

On midsummer noon, the sun cast no shadow in Syene, so must have been directly overhead. In Alexandria, the sun cast a 7° shadow, which is equal to the angle. This is about ¹⁄₅₀ of a circle, so the Syene–Alexandria distance must also be ¹⁄₅₀ of the earth’s circumference.

Eratosthenes worked out the size of the earth 200 years before Christ. He was the head of the famous Library of Alexandria in Egypt. He measured the angles of shadows in two different places on the same day of the year. He already knew the sun cast no shadow during midsummer noon at a place called Syene (Aswan), which was far south of Alexandria.

Where he lived, noon midsummer shadows had an angle of about 7°, or about 1⁄50 of a circle, on that day. He realized that the earth must have a circumference 50 times the distance between the cities, which he knew. His result was very close to the modern value of 40,007 km (24,859 miles).

Design features

Our own planet has many amazing features which no other planets in our solar system have. Here are just a few of them:

Right distance: The earth travels around the sun once per year and is always about 150 million km (93 million miles) from the sun. This is just right! Too close and the oceans would boil. Too far and the oceans would freeze. But at the right distance, most water is liquid, just like we need.

Right spin: The earth spins once per day. This means we have the day and night cycle. Without this cycle, half the earth would always be unbearably hot while the other side was freezing cold. This cycle is so important that God started it on Day 1 of Creation Week, even before He made the sun (Day 4).

Right atmosphere: We need oxygen to breathe, so the air must contain it. But the atmosphere is only 21% oxygen. The rest is nitrogen (78%) and other gases. This is a good thing—much more oxygen would make it impossible to put fires out!

Right substance: Our earth is 72% covered by water. The oceans are vital for sea life—but also for life on the land. Some ocean water evaporates to form clouds, then rain falls on the on the land. The ocean also makes the earth’s temperature more even. The deepest parts of the ocean are so deep that the highest mountains could be swallowed by them. If the earth were perfectly smooth, the ocean water would cover the whole globe 3 km (2 miles) deep.

Right tilt: The earth spins on an axis that is tilted 23.5°. This explains the seasons (see diagram). Without a tilt, there would be no seasons. But it would also mean that the poles would be colder and the equator hotter than they are today. The seasons started on Day 4 of Creation Week (Genesis 1:14). So, we know God created the earth with a tilted axis, on purpose.

In the northern summer, the northern hemisphere receives more of the sun’s rays over a given place. The days are also longer, and the rays pass through less of the atmosphere. So, it is hotter. The southern hemisphere has longer days, and the sunlight is more spread out, so is colder. Six months later, the southern hemisphere has summer while the northern hemisphere has winter.

We know more about Earth than any other planet, because we live here! But for most of history, this was the only planet that astronomers could not see whole. This all changed when the space program began about 60 years ago. Now the whole planet could finally be seen and photographed. Everyone was amazed when they saw its beauty. Astronaut Ron Garan, who was on the International Space Station for six months, said, “When we look down at the earth from space, we see this amazing, indescribably beautiful planet.”

Did the Church teach the earth is flat?

Some atheists claim that the Church taught a flat earth until Columbus sailed around it in 1492. This is utterly false. Almost all Christian writers in history taught that the earth is a globe. For example, 750 years before Columbus, “the Venerable” Bede (AD 673–735), a great scholar who lived in England, said:

“We call the earth a globe … not circular like a shield but rather like a ball ….”

Johannes Sacrobosco wrote a university astronomy textbook called The Sphere in AD 1230. He explained three reasons why the earth must be a ball:

When you climb higher, you can see further away. That’s because we can now see above the ‘curve’ of the earth. This explains why the crow’s nests (lookout platforms) on sailing ships were so high. Sailors also knew that ships disappeared over the horizon bottom first (‘hull down’).

When you travel further east, the sun rises earlier. This is why we divide the earth up into different time zones. Sometimes we (the writers), living in the USA, must talk with our colleagues in Australia. It is usually after dark for us, but bright morning in Australia.

We see different stars as we travel north and south. In Australia and New Zealand, when people look south, they see the Southern Cross. This is on these countries’ flags. People in the UK and USA can’t see the Southern Cross because the earth is in the way! But they can see the North Star (Polaris), which is hidden by the earth in Australia and New Zealand.