Interesting Facts about Our Solar System, Galaxy, and the Universe

In this article, we will answer the most common questions of humanity about our Solar System, Galaxy, and the Universe. But first, let's look at what distinguishes these concepts.

Solar System — a planetary system that includes the central star — the Sun, and all natural cosmic objects (planets, asteroids, comets) united by gravitational interaction.

Galaxy — a gravitationally bound system of stars, star clusters, interstellar gas and dust, dark matter, and planets. Our Solar System is part of the Milky Way galaxy.

Universe — everything that physically exists, a combination of space, time, and the most diverse forms of matter, such as planets, stars, galaxies, and the components of intergalactic space. The Universe is so vast that its size is hard to imagine, and no one knows how large it is.

Which planet in the Solar System is the hottest?

The hottest planet in the Solar System is Venus. The average temperature on its surface is about 470 degrees Celsius. Although Mercury is closer to the Sun, it lacks an atmosphere, so the heat from its Sun-warmed surface radiates freely into surrounding space. Venus, on the other hand, has a dense atmosphere that traps heat due to a powerful greenhouse effect.

Which planet in the Solar System has the largest mountains and the deepest canyons?

In both "categories," the record holder in the Solar System is Mars. This planet hosts the largest mountain in the Solar System — the extinct volcano Olympus. It has a height of about 27 kilometers and a base width of 520 kilometers.

It also has the deepest canyon — the Valles Marineris canyon system. It stretches nearly 4,000 kilometers in length, with depths ranging from 2 to 7 kilometers.

Which planets in the Solar System have rings, and what are they made of?

Today, it is known that all four gas giants — Jupiter, Saturn, Uranus, and Neptune — have rings. Saturn’s rings are the most beautiful and prominent. These formations consist of many solid (icy) bodies, reflecting sunlight, ranging in size from grains of sand to 20–30 meters.

Despite the impressive appearance of the rings, the amount of material in them is extremely small. If all of Saturn's ring material were gathered into a single spherical monolith, its diameter would not exceed 100 kilometers.

In which month is the Earth closest to the Sun, and in which is it farthest from it?

The closest point of a planet’s orbit to the Sun is called perihelion, and the farthest is called aphelion. In the current era, our planet passes through perihelion on January 2–5, and through aphelion on July 1–5.

Interestingly, many people are surprised to learn that Earth is closest to the Sun in January and farthest in July. But only residents of the Northern Hemisphere, where January is the middle of winter, might be surprised by this fact. In the Southern Hemisphere, where only about 10% of the world's population lives, no one is likely to be surprised, as midwinter here is in July.

However, the change of seasons (spring, summer, autumn, winter) does not occur because Earth moves closer to or further from the Sun. Yet, many people still believe this to be the case.

The main reason for the change of seasons is the tilt of Earth's axis, not its distance from the Sun.

In addition to orbiting the Sun, Earth rotates around an imaginary axis (a line passing through the North and South Poles). If Earth's axis were perpendicular to its orbital plane, we would not have seasons, and all days would be the same. Without the axis tilt, the length of day and night would be equal everywhere on Earth, and the Sun would maintain the same position above the horizon throughout the year.

But Earth’s axis is tilted at 23.44° relative to the perpendicular to its orbital plane. This tilt causes seasonal changes on the surface of our planet with a period of one tropical year — 365.24 solar days.

Why doesn’t Mercury have seasons?

Mercury’s rotation axis is nearly perpendicular to its orbital plane, so it has no seasons in the sense that we understand them on Earth. The Sun's rays strike the polar regions of Mercury almost horizontally, creating perpetual winter conditions (the poles are never completely dark because the Sun is much larger than Mercury).

Mercury is the closest planet to our blazing star. However, studies of Mercury suggest that its poles may harbor glaciers (the ice layer can reach two meters and is covered by dust).

What are the size and age of the largest meteorite crater on Earth's surface?

The largest of all craters where meteorite material has been found is the Barringer Crater in Arizona, USA. It is a well-preserved depression about 1,200 meters in diameter and approximately 200 meters deep.

Its rim rises about 50 meters above the surrounding plain. It is believed that erosion has reduced the rim height by 15–20 meters since its formation.

The crater formed around 50,000 years ago after a 50-meter meteorite weighing 300,000 tons struck at about 50,000 km/h. The impact was as powerful as 8,000 atomic bombs like the one dropped on Hiroshima.

Due to its good preservation, this crater is one of the most famous on Earth. It is frequently featured in science documentaries, including by Discovery and BBC. The Arizona crater is a popular tourist attraction in the state. It receives numerous visitors daily.

A museum is located at the crater’s edge, and its official brochure states:

“Although Earth has larger impact traces, this crater was the first to have its meteorite origin proven and is the best preserved.”

The Barringer Crater was recognized as the place on Earth most similar to the lunar landscape, and it was there that part of the training for all astronauts bound for the Moon took place.

What are the size and location of the largest known meteorite crater in the Solar System?

The largest known meteorite crater — Valhalla — is located on Callisto, a moon of Jupiter. It has a bright central area about 600 kilometers in diameter, with a system of concentric ridges extending 1,500 kilometers from the crater’s center.

How dangerous are asteroids?

The danger scale for asteroids, adopted by the International Astronomical Union, is graded from 0 to 10. A zero is assigned to an asteroid whose orbit crosses Earth's orbit but has no chance of collision. A ten marks an asteroid whose impact could cause a global climate catastrophe.

Among the approximately 2,000 asteroids larger than a kilometer that cross Earth's orbit, all are rated zero.

Why is the night sky dark?

If the Universe were infinite in space and time, there would be a star in every direction along the line of sight. The entire surface of the night sky would appear dazzlingly bright, like the Sun’s surface. The contradiction between this statement and what we actually observe is called Olbers' paradox (or the Chesaux-Olbers paradox).

Olbers' paradox, also known as the dark night sky paradox, is an argument in astrophysics and physical cosmology asserting that the darkness of the night sky contradicts the assumption of an infinite and eternal static Universe. The darkness of the night sky is one of the indications of a dynamic Universe, such as the Big Bang model.

This paradox cannot be explained within the framework of a stationary Universe theory. However, it can easily be resolved by considering that the Universe originated from the so-called Big Bang and is only 13.7 billion years old. The farthest objects we can see are no more than 13.7 billion light-years away, and light from more distant objects simply hasn’t reached us yet (the speed of light, as known, is not infinite and is 300,000 kilometers per second). This is why the night sky is dark.

Which star is the brightest?

The brightest star in the night sky is Alpha Canis Major, better known as Sirius (Greek for "sparkling"). This star is visible from any region on Earth, except for the farthest northern regions. It is located 8.6 light-years from the Solar System and is one of the closest stars to Earth.

The diameter of Sirius is almost twice that of the Sun, its mass is 2.35 times that of our star, and its surface temperature is about 10,000 Kelvin (on the Sun's visible surface, it is approximately 6,000 Kelvin). Moreover, Sirius is 25 times more luminous than the Sun.

Due to its relative proximity to us, Sirius' movement across the celestial sphere is significantly more noticeable than that of other stars: in the last 2,000 years, it has shifted about 44 arc minutes, which is one and a half times the diameter of the full Moon. In its motion towards the observer’s line of sight, Sirius is approaching us at a speed of about 8 kilometers per second.

Sirius is a binary star, with its second component being a white dwarf known as Sirius B. It has significantly lower luminosity, making it hard to distinguish alongside the bright Sirius.

How many stars are there in the Universe?

In 2004, Australian astronomers counted all the stars in the visible Universe. To do this, they selected a random square of the sky, measured its brightness, calculated the number of stars based on the average brightness of a star, and extrapolated the result to the entire celestial sphere. The total was 70 sextillion (7 with 22 zeros) stars. This is 10 times more than the number of grains of sand in all the deserts and on all the beaches of Earth.

How old is the Universe, and on what data is this age based?

In 2003, using a NASA-launched space probe equipped with special instruments, measurements were made of the background microwave (relic) radiation temperature with an accuracy of a millionth of a degree. These measurements allowed scientists to establish that the age of the Universe is 13.7 billion years and that the formation of the first generation of stars began 200 million years after the Big Bang.

How large is our Galaxy?

Our Galaxy (the Milky Way) has a complex shape that can be roughly compared to a giant lentil.

The bulk of galactic matter (stars, interstellar gas, dust) occupies a lens-shaped volume about 100,000 light-years in diameter and 12,000 light-years thick at its center. Another (significantly smaller) portion of galactic matter fills a nearly spherical volume with a radius of about 50,000 light-years. The centers of the lenticular and spherical components of the Galaxy coincide.

A Grand Tour of the Planets in the Solar System

A Journey through the Milky Way