The Earth will come extremely close to the Sun: learn why this happens in winter and how you can witness the phenomenon for yourself.

On January 4 at 4:28 PM Moscow time, the distance between the Earth and the Sun will reach its minimum.

Photo: Shutterstock.

On January 4 at 4:28 PM Moscow time, the distance between the Earth and the Sun will shrink to a minimum of "only" 147,117,000 kilometers. If you feel like the Sun appears particularly large, you're not mistaken. We explain why this happens, why the Sun is close even though it's winter, and how you can verify this yourself.

UNATTRACTIVE ORBIT

The Earth orbits the Sun in an ellipse, which is an elongated shape. As a result, the Earth is sometimes closer to the Sun and sometimes farther away, just like all the planets. The Earth is farthest from the Sun at the beginning of July and closest right now. The difference in position is significant: 5 million kilometers.

For centuries, astronomers believed that planetary orbits could only be circular since a circle is a perfect shape, while an ellipse is considered "ugly." This was also the belief of Nicolaus Copernicus, the father of modern astronomy.

However, the real movements of the planets did not align with the hypothetical circles. Finally, Johannes Kepler understood that orbits are ellipses. This realization was not easy for him; he doubted for a long time. Nature couldn't possibly be so "ugly"! Others had their doubts too, but facts are undeniable.

Consequently, if this is true, the Sun should appear to change size. Measuring the apparent size of the Sun is challenging due to its brightness. Only Archimedes managed to do this in the 3rd century BC. Kepler decided to replicate this experiment, using a pinhole camera to avoid glare. A small hole is made in a box, and the "sunspot" observed inside is proportional to the actual disk size. Indeed! The Sun changes its apparent size throughout the year!

SHALL WE CHECK?

It's easy. There are two methods.

You can make a pinhole camera like Kepler did. Take a sturdy box and create a tiny hole, less than a millimeter in diameter. For instance, cut a larger hole, cover it with foil, and poke a small hole in the foil with a needle. Leave the top of the box open so you can see inside.

During these days, carefully draw the Sun's disk inside the box on the side opposite the hole. Then wait until early July. When you repeat the experiment in the summer, you will see that the summer sunspot is noticeably larger than the winter one. The difference will be quite significant.

Alternatively, you can use a small mirror, about one centimeter. If you don't have one, take a regular mirror, cover it with paper, and cut a "peephole" in it.

Let's observe the sunspot. At a distance (about 5 meters or more), it will suddenly transform into... an image of the Sun. You might even see sunspots. Regardless of the shape of the mirror or the hole in the paper, the image will still be round.

Just like before: draw it and compare it with the summer image.

This experiment is a bit more complicated because the distance from the mirror to the screen must remain constant in both winter and summer. The box will remain the same, so measure it and store it until July.

BUT WHY WINTER?

Indeed, how can this be?

Let's ask: what actually determines whether it's warm or cold?

It's often said: it's the distance to the Sun! But as we see, that's not the case. The Sun is close, yet we have winter. This is always the case.

In reality, the angle of the sunlight to the Earth's surface plays a crucial role. In winter, the Sun's rays strike at a slant, barely touching the ground because the Sun is very low. In contrast, during summer, they hit almost straight down. This is why we experience warmth in summer and cold in winter.

It's also important that the low Sun has to penetrate a thick layer of atmosphere, absorbing its heat. In summer, however, the rays from the high-standing Sun lose very little energy.

Moreover, summer in the Southern Hemisphere coincides with perihelion (the closest position of the Earth to the Sun), making it slightly warmer than summer in the Northern Hemisphere, which occurs at aphelion (the farthest position).

A RULER FOR THE SKY

Although the ancients did not know that the Sun moves closer and farther away, they managed to measure (albeit with considerable error) the distances to the Moon and the Sun. Archimedes even estimated the distance to the nearest stars quite accurately, believing they were 2 light-years away when they are actually four.

This is truly hard to comprehend. How??? Without GPS, maps, or telescopes? If we were placed in a desert, naked, we wouldn't be able to find north or south, let alone measure the distance to the Sun.

Let's try to replicate their methods. It's not that difficult.

PEERING INTO A WELL

The foundation of all calculations is the size of the Earth. In meters and kilometers (of course, they used different units of length back then, such as stadia, about 200 m, but that’s irrelevant).

Many measured the size of the Earth in ancient times, with Eratosthenes in the 3rd century BC being the most accurate. He noticed that when the Sun was directly overhead in southern Egypt, it was not directly overhead in Alexandria to the north; it was at a lower angle. He realized that if he measured the distance between these two points in degrees (which is simple to do with a stick and its shadow) and in meters (or stadia), he could determine the size of the entire sphere.

Specifically.

In the city of Siena in the south, the Sun was at zenith. In Alexandria, it was 7.2 degrees away from zenith. The distance between these two points was estimated to be 5,000 stadia. They measured it with caravans, steps, and just by sight. Hence:

7.2 degrees = 5,000 stadia

360 degrees (the circumference of the Earth) = 250,000 stadia.

The error lay in the stadia (it’s hard to measure steps accurately), but the result is good. 40,008 kilometers in circumference compared to the actual 40,075 kilometers. When measuring the Earth, he erred by a mere 67 km!

As a teenager, I corresponded with a peer from Pyatigorsk, and we repeated this experiment. We succeeded, but the result was worse, even though I measured the distance (on the map) accurately. Apparently, the Greeks were better at measuring angles.

HOW TO DETERMINE THE DISTANCE TO THE SUN?

This task was undertaken by the astronomer Aristarchus (also in the 3rd century BC). He aimed to catch the moment when the Moon is exactly half-illuminated. This indicates that the angle between the Sun, the Moon, and the Earth is precisely 90 degrees.

However, when viewed from Earth, measuring the angle between the Moon and the Sun in the sky will yield a different value, not 90 degrees. This is because the Moon and Earth are at different distances from the Sun. This discrepancy holds the key to the truth.

Aristarchus did not have a telescope. By observing the half Moon with his naked eye, he made a significant error. His estimates indicated a deviation of a full 3 degrees (in reality, it was less). This meant that the distance from the Earth to the Sun was 19 times greater than the distance from the Earth to the Moon.

In reality, it's 500 times greater. But it's a start! The scale of the phenomenon was captured, as scientists say.

FINAL CALCULATION

Okay, this is just a proportion, but we need stadia, we need real numbers! Calm down, it's coming.

Aristarchus paid attention to lunar eclipses. This is when the Earth's shadow falls on the Moon. It's clear that the Earth's shadow "expands": just like your shadow appears huge on a wall when you carry a flashlight. However, we know enough to unravel this geometry. We know the proportions, and we know the size of the Earth.

The task is to track during the eclipse the angular size of the Earth's shadow falling on the Moon. Then comes some fairly complex mathematics (which we’ll skip), and here’s the result: