Category Archives: Solar System

A series of articles i wrote for RTL Today in Luxembourg. It gives a simple overview of our Solar System. The Moon, The Sun and the planets (and their moons!) that orbite around it.

Hunting down Planet Nine

It has been nearly a decade since researches at California Institute of Technology (Caltech) noticed irregularities in the orbit of some extreme trans-Neptunian objects (ETNOs) -bodies orbiting the Sun in the outermost region of our Solar System, well beyond Neptune. What was causing the strange behaviour? Have we cracked the mystery?

When Caltech astronomers Konstantin Batygin and Mike Brown first published their research showing evidence of a giant planet in the outer Solar System in 2015, they certainly made the headlines. The announcement came nearly 170 years after the discovery of Neptune, the latest planet to be found orbiting the Sun.

The two researchers had used detailed mathematical modelling and complex computer simulations to explain the odd orbital behaviour of some dwarf planets and other smaller icy bodies in the Kuiper Belt, the outskirts of the Solar System. The explanation, they proposed, was the gravitational pull of an elusive planet, which they dubbed “Planet Nine”.

Read also: The Mysteries of Outer Space.

Other possible explanations were considered, too. In fact, the debate in the scientific community about whether Planet Nine exists is still ongoing. The most sceptical astronomers tend to minimise, calling out some “ghosts” or biases in the data. A more moderate wing believes we should be looking for a primordial black hole instead, or perhaps some new physics. The enthusiast astronomer, on the other hand, is still out there looking for Planet Nine.

But what is it that they’re looking for exactly? According to scientists, the mysterious world has a mass about 5 to 10 times that of Earth, and it could look anything from a rocky super-Earth to a gaseous mini-Neptune, perhaps sharing characteristics with Uranus or Neptune.

Artist impression – Planet Nine

One thing we know for sure is that spotting a celestial body in the vastness of space is not exactly a straightforward task. Besides, Planet Nine is believed to be orbiting the Sun in a highly elongated orbit far beyond Pluto, and considering its elusive nature, it may well be at the far edge of its enormous orbit, meaning it would move quite slow (relative to us) and reflect little to no sunlight.

While this most certainly adds difficulty to the quest, astronomers are confident that modern telescopes around the world are powerful enough to at least spot the elusive world, thus the hunt continues. New data is being acquired and paired or compared with old data: in fact, the truth may hide somewhere in there.

Will we find Planet Nine? And if we do find it, will tradition be followed, and the planet be named after a mythological roman god?*

Personally, I would be delighted to know there really is a Planet Nine lurking in the outskirt of the Solar System. This would be a sensational discovery, with a lot of new science to come! At the same time, I would be even more thrilled if we finally found evidence for a primordial black hole, and right in our backyard!

Spotting one, of course, would be way more problematic.

* Konstantin Batygin and Mike Brown dubbed their predicted object “Planet Nine,” and the name has been used ever since (along “Planet X”). However, it is the person who actually discovers the planet to get the right to name it (pending approval from the International Astronomical Union).

The mysteries of outer space!

The inner Solar System is a spectacular show of planets and moons dancing around the Sun on the notes played by Gravity. But there is something else lurking in the shadows of the outer Solar System, a cold home to millions of floating icy bodies, asteroids and comets. It is also the home of former planet Pluto!

The outer Solar System is that region of Space beginning right after Neptune’s orbit at around 30 Astronomical Units (AUs) from the Sun, where 1 AU is the average distance between Earth and the Sun (roughly 150 million km or 93 million miles). It is an extremely cold place, with temperatures close to the absolute zero (approx. -270 C); here even hydrogen freezes.

The outer Solar System is composed of two main areas: the Kuiper Belt and the Oort Cloud. The two form a relatively vast area that extends to a distance between 50,00 and 200,000 AUs, according to some estimations. Here, the gravitational field of the Sun progressively loses its strength, and interplanetary space begins.

The Kuiper Belt

Also referred to as the “third zone”, the Kuiper Belt is a donut-shaped region that comprises millions of tiny, icy objects that are thought to be remnants of the early formation of the Solar System.

As these trans-Neptunian objects (TNOs) often collide with each other, they produce even smaller objects, in particular comets and dust.

Comets are wandering bodies of frozen gases, rock and dust; as they orbit the Sun, they gradually melt leaving behind a visible tail. Today, astronomers count a trillion or more short-period comets originating in the Kuiper Belt. These are comets that take less than 200 years to complete an orbit around the Sun.

The Kuiper Belt is also home to relatively larger bodies, the most famous being Pluto. Discovered in 1930, Pluto was initially classified as a planet before being downgraded to “dwarf planet” by the International Astronomical Union in 2006, having failed to clear the area around its orbit.

Sometimes called “The King of the Kuiper Belt”, Pluto is a very peculiar dwarf planet. It rotates counter-clockwise (like Uranus), has its own atmosphere, which is mainly made of nitrogen and methane, and has a surface temperature that varies between about -235 C and -210 C. It also has five moons: Charon, Hydra, Nix, Kerberos and Styx.

Other dwarf planets in the Kuiper Belt include Eris (one of the largest in the Solar System), Haumea and Makemake.

Dwarf planet Pluto – Credit: NASA ®

The Oort Cloud

The Oort Cloud is a large region of space made of millions of icy bodies circling the entire Solar System, marking its frontiers. Toward the end of the cloud the Sun’s gravitational pull is less significant and the influence of nearby stars begins to appear.

From this area originate a large number of long-period comets, which have their orbit around the Sun completed in up to thousands of years. The extreme distance from Earth makes it difficult for astronomers to identify the tiny bodies that compose the Oort Cloud and so far only 5 objects that are believed to belong to this area were detected.

Among these there is Sedna, a dwarf planet about three-fourth the size of Pluto that wanders happily in the Oort Cloud at a distance of approximately 900 AU from the Sun, completing an orbit around it in around 10,500 years. Sedna’s most distinctive feature, however, is its reddish colour. It is the second-reddest object in the Solar System, after Mars.


With a mass two-and-a-half times that of all the other planets combined, Jupiter is by far the largest planet in the Solar System, earning the well-deserved title of King of planets. Compared to the Earth alone, it is around three hundred times more massive and has a volume exceeding that of our own planet by one thousand-fold.

But that’s not all! Jupiter also stands on the podium as the third-brightest object in the night sky after, well of course the Moon, and Venus. And you don’t need a telescope to spot it, you can easily observe it with the naked eye: it’s so big and bright that you can’t miss it.

Another interesting characteristic is that owing to its fast rotation, the fastest in the Solar System, a day on Jupiter lasts somewhat less than 10 hours…a perfect place to work!

On the other hand, the planet takes slightly less than 12 years to complete its orbit around the Sun; only Neptune takes longer with 164.9 years.

Credit: NASA ®

Jupiter is also referred to as “Gas Giant” due to its gaseous composition, mainly hydrogen and helium, which mimics that of a star; and while some heavier metals may be present in its core, the planet has no solid surface or terrain of any kind.

Its upper atmosphere is made of several bands or clouds of different colour and shape, resulting from countervailing winds tearing east and west across Jupiter.

The most recognisable feature is the Great Red Spot, a giant anticyclonic storm with winds peaking at more than 600 km/h. Observed for the past 150 years (probably even longer), it is the largest known in the Solar System: to have a comparable idea of its size, just think that our planet Earth could comfortably fit within it…twice!

With 79 known moons at the time of this article, Jupiter is second only to Saturn (82 moons) in the Solar System; the four largest moons (Ganymede, Callisto, Io and Europa), named “Galilean moons” after Galileo Galilei, the Italian astronomer who first discovered them in 1610, are among the largest satellites in the Solar System: Ganymede, the largest of them, has a diameter greater than that of the planet Mercury.

Credit: NASA ®

Of the four Galilean moons, however, Europa is the one that most captures scientists’ attention as it hosts one of the key requirements for life as we know it: liquid water.

In the past 40 years or so, in fact, scientists have found strong evidence leading to believe that underneath the thick ice crust that makes most of Europa’s surface lies an ocean 60 to 150 km deep, which is widely considered the most promising place to look for life beyond Earth in the Solar System!

While, according to scientists, life in this bottomless ocean is most likely to be found in the form of microbes, however, an important question arises: would the inhabitants of Europa be called Europeans?


Venus, named after the Roman goddess of love and beauty, is one of the four rocky planets in our Solar System and the second closest to the Sun. It is also the second-brightest celestial object in the night sky after the Moon, shining so bright that it is immediately recognisable to the naked eye and is therefore called “morning star”, when it vaults in the eastern horizon before dawn, or “evening star” when it is the first “star” to appear in the sky after sunset.

Often referred to as the Earth’s sister or twin, owing to the very similar size, mass and proximity to our star, Venus is in reality much different from our planet on several other aspects.Unlike Earth and most planets in the Solar System, Venus in fact rotates clockwise thus having the Sun rising in the west and setting in the east.

Also, it spins so slow (the slowest in the Solar System), that one day there lasts the equivalent of 243 Earth days. By contrast, the planet orbits the Sun every 224.7 Earth days: on Venus, a year is shorter than a day!

With a temperature of roughly 470 degrees Celsius (880 F), Venus is by far the hottest planet in our solar system; its surface is a dry and dusty desertscape made up of mountains, valleys and thousands of active volcanos, which periodically resurface the planet.

Regardless of the unfriendly conditions, in 1981 a Soviet Union space probe, Venera 13, was able to crash-land on Venus’ surface; the lander survived 127 minutes (despite being designed to last 30 minutes) and was able to transmit the first colour images of the Venusian landscape.

Venus’ extreme conditions depend largely on its thick and toxic atmosphere, which is mostly made up of carbon dioxide, with clouds of sulphuric acid droplets that trap all the Sun’s heat.

However, the atmosphere has many layers and at the level where the clouds are, the temperature is milder, resembling that of our Planet’s surface.

It is also for this reason that part of the scientific community has long believed that some sort of alien life, most likely microorganisms, may hide within the planet’s upper atmosphere.

And a confirmation to this hypothesis may just have come from a recent discovery. Only few weeks back, in fact, an international team of astronomers confirmed the detection in the cloud of Venus of a phosphine, a toxic gas generally considered as a biomarker, a potential sign of life.

This is because back on Earth, phosphine is produced by microbes in oxygen-free environments, like for example inside penguins’ guts, or via some industrial processes.

While scientists believe that Venus does not host all the necessary conditions for the natural production of phosphine, the quantities detected suggest that something must indeed be restocking it.

However, the team has remained very cautious on the nature of their finding, and only further researches will tell us what astronomers have really found; but be this alien life or a previously unknown chemical process, it remains an interesting and exciting discovery.


The fourth planet from the Sun and the second-smallest planet in the Solar System is a mysterious, dynamic world once flooded with liquid water, and today frozen into a desert of spectacular dunes, large valleys and extremely tall volcanoes. This, and much more, is Mars, the Red Planet.

Named after the Roman god of war, Mars is usually referred to as the Red Planet due to the large presence of iron oxide (rust) in its surface, which gives the planet that flaming reddish appearance that makes it so distinctive among the astronomical bodies visible in our night sky.

Mars is approximately half the Earth size but its rotational period as well as the tilt of the rotational axis relative to the orbit are comparable to those of our home planet, meaning that a Martian day or “sol” (short for solar day) is only roughly 40 minutes longer than a Earth day. A Martian year on the other hand lasts the equivalent of 687 Earth days.

Other similarities with our planet include the presence of distinct seasons, polar ice caps, vast canyons as well as very high volcanoes. One of these, Olympus Mons, is the largest volcano and highest known mountain in the Solar System: it is 25 km tall, around three times taller than Mount Everest.

Credit: NASA ®

In 1877, during a close approach of Mars and Earth, two relatively small and irregularly shaped natural moons were discovered orbiting the Red Planet: Deimos (12.6 km in diameter) and Phobos (22.2 km).

The latter is of particular significance as it is on a collision course with its host planet, getting 1.8 metres closer each century: it is estimated that the two will meet closely in around 50 million years.

Scientific evidence proves that millions of years ago Mars had lakes and rivers of liquid water flooding its surface. The lack of a magnetic field, however, caused the majority of the Martian atmosphere to be destroyed and dispersed into space by the strong solar wind, according to NASA, turning the Red Planet into a frozen world with an average surface temperature of -62°C and peaks as low as -143°C.

Nevertheless, water on Mars can still be found today in the form of ice and in such quantities that, if melted, it would be sufficient to cover the planetary surface to a depth of 11 metres.

This is a fundamental notion as NASA as well as other space organisations plan to establish a permanent human colony on Mars in next decades. We can expect some really exciting times ahead!


Considered by many the most beautiful planet in the Solar System, with its breath-taking colours and spectacular ring system, Saturn is arguably the most iconic of all planets. The features of this Gas Giant are so unique that a simple glance at this beautiful world through a telescope is likely to turn an unwary observer into an astronomer forever!

Although the first observation through a telescope was only done in 1610 by Galileo, Saturn is known to humanity since ancient times. The Romans named it after their god of agriculture and harvest before they went on to name a day of the week after it, no later than the 2nd century (Saturday from “Saturni dies” or “Saturn’s Day”).

Over 95 times more massive than Earth, and with an average radius of about nine times that of our home planet, Saturn is the second largest planet in our solar system, after Jupiter.

At a distance of 1.4 billion km, it is the sixth planet from the Sun and the farthest planet from Earth to be visible to the naked eye with its steady yellow glow.

What is not visible to the naked eye, however, is Saturn’s most distinctive and spectacular feature: its prominent structure of seven rings separated by gaps and divisions, with the Cassini division as the largest and most obvious.

The rings are largely made of tiny chunks of ice along with rocky debris and dust, which according to NASA are pieces of comets, asteroids or shattered moons that were torn apart by Saturn’s powerful gravity.

The body of Saturn, on the other hand, is a Gas Giant much like Jupiter, made of hydrogen and helium with a presence of ammonia crystals in its upper atmosphere that confer the planet that distinctive pale-yellow hue among shades of brown and grey.

In line with its fast-rotating magnetic field, the ringed planet spins on its axis fast enough to claim the second-shortest day in the solar system (slightly below 11 hours) while a complete orbit around the Sun (a Saturnian year) lasts about 29.4 Earth years. Moreover, the tilt of its axis, somewhat similar to that of our planet, suggests that Saturn too experiences seasons.

Another interesting characteristic that once again emphasises the gigantic size of Saturn, is the incredible number of moons that orbit the ringed planet. At the time of this article, in fact, Saturn boasts 82 known moons, of which the biggest, Titan, is the second largest in the Solar System, bigger than the planet Mercury!

But it is not just the size that makes Titan interesting; this rocky world is the only moon in the Solar System known to have a dense atmosphere and the only place besides Earth known to have liquids in the form of rivers, lakes and seas on its surface.

While these waters are mainly made of liquid hydrocarbons like methane and ethane, liquid water more similar to what we are accustomed to is present beneath Titan’s thick crust of water ice. It is this abundance of liquids that makes Titan a serious candidate in our search for extra-terrestrial life in the Solar System!


Probably the least famous planet in our Solar System, Uranus is without doubts one of the most exceptional and unique worlds. Flipped on one side as a result of a massive collision, this cyan-tinted world hides unexpected wonders and unique features: extreme seasons, astonishing rings and…orbiting moons named after Shakespeare’s characters!

Observed since ancient times, with first observations tracing back to Hipparchos (128 BC), Uranus was the first planet to be recognised as such with the aid of a telescope. For centuries, in fact, the planet had been mistaken for a star before Sir William Herschel pointed his homemade 7-foot telescope at it, in 1781.

And even then, he thought he was glancing at a comet. It was only after few years that the object was universally accepted as another planet orbiting the Sun. The discovery gained Herschel the official protection of King George and the astronomer, to express his gratitude, proposed to name the planet after the King.

Finally, the recent discovery of a new metal (Uranium) led the scientific community to accept another of the proposed names: Uranus, the Greek god of the sky.

Uranus is the seventh planet from the Sun at 2.9 billion km and has the third-largest diameter and the fourth-largest mass in the Solar System. Compared to Earth, it is 4 times wider: by comparison, if our planet were a tennis ball, Uranus would be a basketball.

But size is not what makes it unique and bizarre. Possibly the result of a massive collision, Uranus’ axis is tilted about 98 degrees (Earth’s tilt is 23.5) meaning it appears flipped on one side, with one of its poles pointing toward the Sun. It is the only planet in the Solar System spinning almost on its side!

Another peculiarity of this Ice Giant is that, along Venus, it is the only planet in the Solar System to rotate counterclockwise, with the Sun rising in the west.

A day on Uranus is relatively short at 17 hours whereas a year, the time Uranus takes to make a complete orbit around the Sun, takes around 84 Earth years, a full human life.

And that is not all. The extreme tilt of the axis also contributes to the planet’s weird seasons with the northern hemisphere experiencing 21 years of continued day light in summer, 21 of years of dark in winter and 21 years of equally split daylight and night-time in the spring and fall.

Credit: NASA ®

Together with Neptune, Uranus is usually classified as “Ice Giant”. The “Ice” refers to the composition of the mass that contains a hot dense fluid of water, ammonia and methane, which planetary scientists tend to call “ices”, for they solidify at cold temperatures. And never mind the fact that inside the atmosphere these ices boil under the extreme pressure. They still classify as “ices”.

The atmosphere is mostly hydrogen and helium, but it is methane that confers Uranus its distinctive pale blue colour. As seen in other giant planets, the upper atmosphere experiences extreme storms with winds up to 900 km per hour in the direction of rotation. The planetary temperature is the coldest in the Solar System with peaks at -224 °C.

Like Saturn, Uranus has its own systems of rings: 13 ultra-thin hoops of tightly packed icy rocks and dust that encircle the planet vertically rather than horizontally, due to the extreme tilt of the planet’s axis.

Uranus has also 27 known moons in its orbit, largely composed of ice water and rock. They are named after the characters from the works of William Shakespeare and Alexander Pope: from Juliet and Ophelia to Ariel and Umbriel, Uranus is certainly in good company.


Named after the fleet-footed Roman god, Mercury is the smallest planet in the Solar System and the closest to the Sun, so close that it has been tricking astronomers for centuries. Hidden behind the extremely bright glare emitted by our host star, Mercury can only be observed in the either morning or evening twilight, for short period of times.

Failure to observe this elusive planet did not spare big star astronomers such as Copernicus, who blamed the miserable weather condition in northern Poland, and Kepler, who predicted the planet’s rare transit in front of the Sun in November 1631 only to die a year earlier missing out on the opportunity.

Even NASA’s Hubble Space Telescope avoided glancing at Mercury to prevent potential damage to its optics. It is no surprise then that the first detailed images only came in between 1974 and 1975, when the Mariner 10 space probe completed three close flybys of the mysterious planet.

The thousands of pictures taken by NASA’s space probe revealed a view of Mercury that seemed oddly familiar to us all: it looks a lot like The Moon!

From its greyish-brown appearance to the impact craters scattered all over the surface and the brighter streaks called “crater rays” that spread out from them. The two are even similar in size, with Mercury just slightly bigger than The Moon.

The proximity with the Sun affects the planet in several ways. At only 58 million km (36 million miles) distance, the gravitational pull exerted by our star is extreme and fuels Mercury up to a speed of 47km (29 miles) per second. At this speed it takes the planet only 88 Earth days to complete a full orbit around the Sun, a Mercurian year.

On the other hand, that same gravitational pull has a breaking effect on the planet’s spin to such an extent that Mercury completes a rotation on its own axis in 58.6 Earth days.

However, due to its elliptical, fast orbit, a full spin is not accompanied by a sunrise and sunset like it is on most other planets when Mercury is at its closest distance from the Sun. In such phase, a day measured as day/night cycle lasts 176 Earth days, or a little over 2 Mercurian years.

Without a mitigating atmosphere, the planet temperatures are heavily influenced by the Sun too, reaching extreme highs (approx. 430° C) where the surface is lit, before dropping to extreme lows (-180° C) at night. There are no seasons on Mercury, unlike most planets, as its axis is tilted just 2 degrees with respect to its orbit around the Sun.

Credit: NASA ®

Despite being a terrestrial planet with ice water potentially hidden at its north and south poles inside deep craters, in regions of permanent shadow, Mercury is not seen as a potential candidate for hosting life.

It does not have any spectacular rings or any moons in its orbit but can boast a main role in one of the most important scientific discoveries of all times!

In 1859 the French astronomer Leverrier, famous for having successfully predicted the existence of Neptune, announced a redundant anomaly in Mercury’s orbit, which he suggested it may have been the gravitational effect of yet another undiscovered planet.

The search for this hidden planet went on for decades without success until the mystery was finally solved in 1915 with the discovery that revolutionised the understanding of the universe-Einstein’s theory of relativity.

When he first announced his ingenious theory, Einstein shocked the whole world. He had shown how Newton’s laws were incomplete by demonstrating how space itself is warped by the extreme gravitational field in proximity of a large celestial body. It was a sensational discovery and incredible theory that was soon globally accepted.

The theory of relativity revealed how the Sun’s extreme gravitational field distorted space around it causing the change in Mercury’s orbit.

Einstein himself expressed great joy when his relativity-founded calculations of Mercury’s orbit were verified by the observations. He soon became the first scientist celebrity and some credit, perhaps, goes to Mercury too.


The farthest planet from the Sun, Neptune, is an Ice Giant that likely formed closer to our host star before shifting to the outer solar system around 4 billion years ago. At an average distance of 4.5 billion km (2.8 billion miles), it is the only planet in our solar system not visible to the naked eye. At such distance, it takes the light approximately 4 hours to travel from the Sun to Neptune!

The blue giant was the first planet whose existence was predicted by mathematical calculations. A series of irregularities observed in Uranus’ orbit, in fact, led 19th century astronomers to believe that the influence of an undiscovered planet could be the reason behind these anomalies.

Among these was French astronomer Urbain Le Verrier, who in 1845 began his calculations to determine the position of the new planet. It was then in 1846 that the German astronomer Johann Galle, using those predictions, was finally able to point a 9.6-inch telescope at Neptune, to observe it in all its beauty.

And Le Verrier? Well, he passed into history as “the discoverer of a planet with the point of his pen” and, once aware about the correctness of his calculations, he claimed the right to choose the new world’s name: Neptune, the Roman god of the sea.

The name was a clear reference to the planet’s vivid blue tint, that at the time was thought to be due to liquid water floating on the planet’s surface. However, while there is in fact a mix of water, ammonia, and methane ices on the surface (hence the appellative Ice Giant), Neptune’s blue colour is the effect of the small amount of methane present in its atmosphere, which absorbs red light and reflects blue light outward.

The atmosphere, mostly made up of hydrogen and helium, is characterised by extreme winds that can reach up 2,400 km/h (1,500 mph), by far the fastest in our Solar System. Approximately three times stronger than Jupiter’s and nine times stronger than Earth’s, these winds stir clouds of frozen methane across the planet.

Credit: NASA ®

Neptune’s rotation axis is tilted 28 degrees, similar to that of our planet, meaning the Ice Giant too experiences four distinct seasons, although each lasts a little over 40 years. This is because Neptune takes around 165 Earth years to complete an orbit around the Sun, a Neptune year. A day on the blue planet, on the other hand, is relatively short at about 16 hours.

Like its neighbour Uranus, Neptune too has its own ring system, which is made up of 5 main rings and four prominent ring arcs and, according to NASA, it is believed to be relatively young.

At the time of this article, 14 moons have been discovered orbiting around Neptune, the largest being Triton, discovered by British astronomer William Lassell* just 17 days after Galle spotted the planet for the first time.

Triton is quite interesting for scientists as it is the only moon in the Solar System to orbit its planet in a direction opposite to the planet’s rotation; this characteristic is called a retrograde orbit and may be explained by the fact that Triton once was an independent object that was then captured by Neptune’s gravity.

Also, due to its distance from the Sun, Triton is extremely cold, with surface temperatures reaching low peaks of -235 degrees C (-391 degrees F), but its thin atmosphere is getting warmer, leaving scientist without an exaplanation to this day.

*Lassell was a Liverpool businessman who made a fortune in the brewery business and he used this fortune to finance his hobby and his innovative telescopes, including the one used to discover Triton. It is then safe to say that we owe the discovery of this moon to beer!

The Sun

The Sun, that beautiful ball of gas that lights our days on Earth, is the closest star to us and the centre of our Solar System; it allows all sort of life on our planet and provides us with light and warmth.

But what is a star exactly? Confucius once said, “stars are holes in the sky from which the light of the infinite shines”. While I do love this quote, is it all there is to it? How do stars form? And how do they work?

Well, stars are extremely hot and shining celestial bodies that form from clouds of space gas (mostly hydrogen and helium) and dust coming together due to gravitational attraction. As more and more particles are attracted to each other, the pressure from gravity increases causing the material at the centre to heat up.

Throughout their life, stars are then supported against their own gravity thanks to the thermonuclear fusion that happens in their core, which converts hydrogen into helium releasing huge amounts of photons (light) and energy into space.

When small and medium sized stars run out of hydrogen, their life comes to an end and all they leave behind is their core, which then slowly cools down. Massive stars, on the other hand, are so hot that they are able to fuse heavier metals such as helium and carbon before exploding in spectacular supernovae, leaving behind their core to become a neutron star or, for stars over a certain mass, black holes.

The Sun is a medium sized star, categorised as a yellow dwarf star. Nevertheless, it is the largest object in our Solar System, accounting for 99.8% of the total mass: it would take approximately 1.3 million Earths to fill it all!

Its immense gravitational attraction is what holds the Solar System together, keeping planets, moons and all sort of objects around its orbit.

The Sun with a massive prominence – Credit: A. Anfuso ®

Obviously, our host star is of particular importance to us as well. The light and heat it radiates is what makes life on Earth possible: they give the plants the energy they need to grow and produce food and oxygen. The Sun also drives the seasons, the weather, ocean currents, climate and those breath-taking auroras we all love.

Formed approximately 4.5 billion years ago, according to scientists, the Sun is halfway through its lifetime, which will end in around 5 or 6 billion years.

It is believed that, when approaching the end of its life, the Sun will become so big that it will swallow Mercury and Venus, the closest planets, and potentially even Earth.

The Sun, and with it the whole Solar System, are located in a spiral arm of our galaxy, the Milky Way. From there, it orbits the centre of the galaxy at an average speed of 720,000 kmh (450,000 mph) completing a full orbit in around 230 million years.

Earth lies at an average distance of approximately 149,600,000 km (92,900,000 miles) from the Sun, which is the equivalent of 1 astronomical unit (AU).

At this distance, the Sun is only 8 light minutes away from us, meaning that if the Sun were to go suddenly dark, we would only realise it after 8 minutes. By comparison, the second closer star to Earth is Proxima Centauri, which lies some 4.5 light years away.

The composition of the Sun can be divided into six layers: the core, the radiative zone and the convective zone form the interior structure whereas the photosphere, the chromosphere and the corona (crown) are part of the visible surface.

Temperatures vary dramatically, from 15 million degrees C (27 million degrees F) at the core, to around 5,500 degrees C (10,000 degrees F) at the photosphere.

The chromosphere, alongside the Corona, is perhaps the most interesting layer. At this level, it is possible to detect the Sun’s active regions or “sunspots”: these are areas of extreme magnetic field from which most solar storms, including solar flares and coronal mass ejections (CME), are formed.

Another shot at the Sun – Credit: A. Anfuso ®

The sunspots are a clear indicator of the solar activity as it goes through the phases of its own solar cycle, which last approximately 11 years. During “Solar maximum” the number of active regions, solar flares and coronal mass ejections increases dramatically, whereas at “Solar minimum” the number of sunspots tends to fade.

This is particularly important because such irregularities in the Sun’s magnetic field can release huge amounts of energy that, although not dangerous for life on hearth, can damage satellites and pose a risk for astronauts in space.

Seen through a telescope with the right filter (never look at the Sun without a proper filter!), the Sun is a jaw-dropping view, perhaps one of the most interesting sights in our Solar System. If you’re interested in imaging the Sun, check out my guide by following this link: A deeper look into Solar Imaging.

To conclude with a quote: “The Sun is not God, though His noblest image” (Robert Dodsley).

Solar Gallery