The Sun


The Sun or Sol, is the star at the centre of our solar system and is responsible for the Earth’s climate and weather. The Sun is an almost perfect sphere with a difference of just 10 km in diameter between the poles and the equator. The average radius of the Sun is 695,508 km (109.2 x that of the Earth) of which 20–25% is the core.

Star Profile

Age: 4.6 Billion Years
Type: Yellow Dwarf (G2V)
Diameter: 1,392,684 km
Circumference at Equator: 4,370,005.6 km
Mass: 1,989,100,000,000,000,000,000 billion kg (333,060 x Earth)
Surface Temperature: 5500 °C

Facts About The Sun

One million Earths could fit inside the Sun:
If a hollow Sun was filled up with spherical Earths then around 960,000 would fit inside. On the other hand if these Earths were squished inside with no wasted space then around 1,300,000 would fit inside. The Sun’s surface area is 11,990 times that of the Earth’s.

Eventually, the Sun will consume the Earth:
When all the Hydrogen has been burned, the Sun will continue for about 130 million more years, burning Helium, during which time it will expand to the point that it will engulf Mercury and Venus and the Earth. At this stage it will have become a red giant

The Sun will one day be about the size of Earth:
After its red giant phase, the Sun will collapse, retaining its enormous mass, but containing the approximate volume of our planet. When this happens, it will be called a white dwarf.

The Sun contains 99.86% of the mass in the Solar System:
The mass of the Sun is approximately 330,000 times greater than that of Earth. It is almost three quarters Hydrogen, whilst most of the remaining mass is Helium.

The Sun is an almost perfect sphere:
There is only a 10 kilometre difference in its polar diameter compared to its equatorial diameter. Considering the vast expanse of the Sun, this means it is the closest thing to a perfect sphere that has been observed in nature.

Light from the Sun takes eight minutes to reach Earth:
With a mean average distance of 150 million kilometres from Earth and with light travelling at 300,000 kilometres per second, dividing one by the other gives us an approximate time of 500 seconds, or eight minutes and 20 seconds. Although this energy reaches Earth in a few minutes, it will already have taken millions of years to travel from the Sun’s core to its surface.

The Sun travels at 220 kilometres per second:
The Sun is 24,000-26,000 light years from the galactic centre and it takes the Sun 225-250 million years to complete an orbit of the centre of the Milky Way.

The distance from the Sun to Earth changes throughout the year:
Because the Earth travels on an elliptical orbit around the Sun, the distance between the two bodies varies from 147 to 152 million kilometres. The distance between the Earth and the Sun is called an Astronomical Unit (AU).

The Sun is middle-aged:
At around 4.5 billion years old, the Sun has already burned off about half of its store of Hydrogen. It has enough left to continue to burn Hydrogen for approximately another 5 billion years. The Sun is currently a type of star known as a Yellow Dwarf

The Sun has a very strong magnetic field:
Solar flares occur when magnetic energy is released by the Sun during magnetic storms, which we see as sunspots. In sunspots, the magnetic lines are twisted and they spin, much like a tornado would on Earth.

The temperature inside the Sun can reach 15 million degrees Celsius:
At the Sun’s core, energy is generated by nuclear fusion, as Hydrogen converts to Helium. Because hot objects generally expand, the Sun would explode like a giant bomb if it weren’t for its enormous gravitational force.

The Sun generates solar wind:
This is a stream of charged particles, which travels through the Solar System at approximately 450 kilometres per second. Solar wind occurs where the magnetic field of the Sun extends into space instead of following its surface.


Name		Distance from Sun		Type
Mercury		57,909,227 km (0.39 AU)		Planet
Venus		108,209,475 km (0.73 AU)	Planet
Earth		149,598,262 km (1 AU)		Planet
Mars		227,943,824 km (1.38 AU)	Planet
Ceres		413,700,000 km (2.77 AU)	Dwarf Planet
Jupiter		778,340,821 km (5.20 AU)	Planet
Saturn		1,426,666,422 km (9.58 AU)	Planet
Uranus		2,870,658,186 km (19.22 AU)	Planet
Neptune		4,498,396,441 km (30.10 AU)	Planet
Pluto		5,874,000,000 km (39.26 AU)	Dwarf Planet
Haumea		6,452,000,000 km (43.13 AU)	Dwarf Planet
Makemake	6,850,000,000 km (45.79 AU)	Dwarf Planet
Eris		10,120,000,000 km (68.01 AU)	Dwarf Planet

Asteroid Belt

astroid belts

What Is The Asteroid Belt?

The vast majority of asteroids in the solar system are found in a region of the solar system out beyond Mars. They form the Asteroid Belt. Others orbit in near-Earth space and a few migrate or are thrown out to the outer solar system by gravitational interactions. The four largest asteroids in the belt are Ceres, Vesta, Pallas, and Hygiea. They contain half the mass of the entire belt. The rest of the mass is contained in countless smaller bodies. There was a theory once that if you combined all the asteroids they would make up the missing “Fifth” rocky planet. Planetary scientists estimate that if you could put all that material together that exists there today, it would make a tiny world smaller than Earth’s moon.

Where Is The Asteroid Belt Located?

The Asteroid Belt is located in an area of space between the orbits of Mars and Jupiter. That places it between 2.2 and 3.2 astronomical units (AU) from the Sun. The belt is about 1 AU thick. The average distance between objects in the Asteroid Belt is quite large. If you could stand on an asteroid and look around, the next one would be too far away to see very well.

Asteroid Mining

The solar system contains many different types of asteroids, grouped by the minerals they contain. The abundances of precious metals such as nickel, iron, and titanium (to name a few), and water make asteroids an attractive target for mining operations when humans decide to expand their presence through interplanetary space. For example, water from asteroids could serve colonies in space, while the minerals and metals would be used to build habitats and grow food for future space colony inhabitants. Beginning 2013, companies interested in asteroid mining began announcing their plans for future operations on distant planetoids. In addition, NASA is looking into similar missions. The biggest obstacles to asteroid mining are the need to develop affordable spaceflight technology that would allow humans to get to the asteroids of interest.

Facts About The Asteroid Belt

What other fascinating things do we know about the Asteroid Belt?

*Asteroid Belt objects are made of rock and stone. Some are solid objects, while others are orbiting “rubble piles”.

*The Asteroid Belt contains billions and billions of asteroids.

*Some asteroids in the Belt are quite large, but most range in size down to pebbles.

*The asteroid 1/Ceres is also designated as a dwarf planet, the largest one in the inner solar system.

*We know of at least 7,000 asteroids.

*The Asteroid Belt may contain many objects, but they are spread out over a huge area of space. This has allowed spacecraft to move through this region without hitting anything.

*Asteroids get their names from suggestions by their discoverers and are also given a number.

*The formation of Jupiter disrupted the formation of any worlds in the Asteroid Belt region by   scattering asteroids away. This caused them to collide and break into smaller pieces.

*Gravitational influences can move asteroids out of the Belt.

 *The Asteroid Belt is often referred to as the “Main Belt” to distinguish it from other groups of asteroids such as the  Lagrangians and Centaurs.

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Kuiper Belt


What Is The Kuiper Belt?

The Kuiper Belt (sometimes referred to as the Kuiper-Edgeworth Belt) is an area of the outer solar systemthat is estimated to stretch across 20 astronomical units (AU) of space. It contains small solar system bodies made mostly of ices. The ices are frozen volatiles (gases) such as methane, ammonia, nitrogen and water. It also is home to the known dwarf planets Pluto, Haumea and Makemake.

The Kuiper-Edgeworth Belt is named for the astronomers Gerard Kuiper, who theorized about a disk of material in the outer reaches of the solar system, and Kenneth Edgeworth, who had the idea that the outer solar system contained a number of small bodies, perhaps left over from the formation of the Sun andplanets. This region of space is cold enough to support the existence of volatiles more easily than areas closer to the Sun.

Kuiper Belt Location

The Kuiper Belt extends from roughly the orbit of Neptune (at 30 AU out to about 55 astronomical units from the Sun. The main body of this belt covers much of this region, ranging from nearly 40 AU to 48 AU. It is thick in most places and astronomers have described it as being more torus-shaped than a belt would be. Other regions of the Kuiper Belt include a disk of scattered objects that are part of a population of worlds called Trans-Neptunian Objects.

Facts About The Kuiper Belt

The Kuiper Belt could contain hundreds of thousands of icy bodies that range in size from small chunks of ice to worldlets larger than 100 kilometres across.

*Astronomers have tracked most short-period comets from their origins in the Kuiper Belt. These are comets with orbital periods of 200 years or less.

*There could be more than a trillion comet nuclei in the main body of the Kuiper Belt.

*The largest Kuiper Belt Objects are Pluto, Quaoar, Makemake, Haumea, Ixion, and Varuna. These are often also referred to as Trans-Neptunian Objects (TNOs).

*The first mission to the Kuiper Belt and beyond will fly by Pluto in July 2015. It’s called New Horizons and will survey Pluto, Charon and the other moons before heading out to study other Kuiper Belt Objects in the future.

*Astronomers have found structures similar to our Kuiper Belt around at least nine other stars. Hubble Space Telescope imaged discs around the stars HD 138664 in the constellation Lupus, and HD 53143 in the constellation Carina.

*The ices in the Kuiper Belt date back to the formation of the solar system. They contain clues to conditions in the early solar nebula.

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Oort Cloud


What Is The Oort Cloud?

The Oort Cloud is an extended shell of icy objects that exist in the outermost reaches of the solar system. It is named after astronomer Jan Oort, who first theorized its existence. The Oort Cloud is roughly spherical, and is the origin of most of the long-period comets that have been observed.

This cloud of particles is theorized to be the remains of the disc of material that formed the Sun andplanets. Astronomers now refer to those primeval objects as a protoplanetary disk. The most likely theory is that the material now in the Oort Cloud probably formed closer to the young Sun in the earliest epochs of solar system formation. As the planets grew, and in particular as Jupiter coalesced and migrated to its present position, its gravitational influence is thought to have scattered many icy objects out to their present position in the Oort cloud.

The Oort Cloud is very distant from the Sun and it can be disrupted by the nearby passage of a star, nebula, or by actions in the disk of the Milky Way. Those actions knock cometary nuclei out of their orbits, and send them on a headlong rush toward the Sun.

Oort Cloud Location

The inner limits of the Oort Cloud begin at about 2,000 AU from the Sun. The cloud itself stretches out almost a quarter of the way to the nearest star, Proxima Centauri. It is spherically shaped and consists of an outer cloud and a torus (doughnut-shaped) inner cloud.

Facts About The Oort Cloud

Objects in the Oort Cloud are also referred to as Trans-Neptunian objects. This name also applies to objects in the Kuiper Belt.

Some astronomers theorize that the Sun may have captured Oort Cloud cometary material from the outer disks of other stars that were forming in the same nebula as our star.

The Oort Cloud is a reserve of cometary nuclei that contain ices dating back to the origin of the solar system.

No one knows for sure how many objects exist in the Oort Cloud, but most estimates put it at around 2 trillion.

The planetoid Sedna, discovered in 2003, is thought to be a member of the inner Oort Cloud.

Astronomers think that long-period comets (those with orbital periods longer than 200 years) have their origins in the Oort Cloud.

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Solar Eclipse

solar eclipse

What Is A Solar Eclipse?

A solar eclipse is a natural event that takes place on Earth when the Moon moves in its orbit between Earth and the Sun (this is also known as an occultation). It happens at New Moon, when the Sun and Moon are in conjunction with each other. If the Moon was only slightly closer to Earth, and orbited in the same plane and its orbit was circular, we would see eclipses each month. The lunar orbit is elliptical and tilted with respect to Earth’s orbit, so we can only see up to 5 eclipses per year. Depending on the geometry of the Sun, Moon and Earth, the Sun can be totally blocked, or it can be partially blocked.

During an eclipse, the Moon’s shadow (which is divided into two parts: the dark umbra and the lighter penumbra) moves across Earth’s surface. Safety note: do NOT ever look at the Sun directly during an eclipse unless it is during a total solar eclipse. The bright light of the Sun can damage your eyes very quickly.


A total solar eclipse occurs when the Moon completely blocks the solar disk. In a total solar eclipse, the narrowest part of the path (where the Sun is completely blocked and the Moon casts its darkest shadow (called the umbra)) is called the “zone of totality”.

Observers in this path see a darkened Sun (often described as a “hole in the sky”) with the ghostly glow of the solar corona extending out to space. A phenomenon called “Bailey’s Beads” often appears as sunlight shines out through valleys on the lunar surface. If the Sun is active, observers can also see solar prominences, loops, and flares during totality. A total solar eclipse is the ONLY time when it is safe to look directly at the Sun. ALL other solar observations (even in partial phases) require special solar filters so that you do not harm your eyes.

Total solar eclipses have not always been visible from Earth. In the past, the Moon was too close to Earth and during eclipses it completely blotted out the Sun’s disk. Over time, the lunar orbit has changed at the rate of just over 2 cm per year and in the current epoch, the alignment is nearly perfect at times. However, the Moon’s orbit will continue to widen, and in perhaps 600 million years, total solar eclipses will no longer occur. Instead, future observers will see partial and annular eclipses only.


Not every solar eclipse is a total one. When the Moon is farther away in its orbit than usual, it appears too small to completely cover the Sun’s disk. During such an event, a bright ring of sunlight shines around the Moon. This type of eclipse is a called an “annular” eclipse. It comes from the Latin word “annulus” which means “ring”.

The period of annularity during such an eclipse can last anywhere from 5 or 6 minutes to up to 12 minutes. However, even though the Sun is mostly covered by the Moon, enough bright sunlight escapes during annularity that observers cannot ever look at the Sun directly. These events require eye protection throughout the entire eclipse.


A partial solar eclipse occurs when Earth moves through the lunar penumbra (the lighter part of the Moon’s shadow) as the Moon moves between Earth and the Sun. The Moon does not block the entire solar disk, as seen from Earth. Depending on your location during a partial eclipse, you might see anything from a small sliver of the Sun being blotted out to a nearly total eclipse.

To view any eclipse safely, use approved filters or use an indirect method of viewing, such as projecting sunlight through a telescope and onto a white piece of paper or cardboard. NEVER look at the Sun through a telescope unless it has the appropriate filter. Blindness and severe eye damage can result due to improper observation technique.   

Facts About Solar Eclipses

Depending on the geometry of the Sun, Moon, and Earth, there can be between 2 and 5 solar eclipses each year.

Totality occurs when the Moon completely obscures Sun so only the solar corona is showing.

A total solar eclipse can happen once every 1-2 years. This makes them very rare events.

If you lived at the North or South Pole, you would see only partial solar eclipses. People in other parts of the world can see partial, total, annular, and hybrid eclipses.

The longest a total solar eclipse can last is 7.5 minutes.

The width of the path of totality is usually about 160 km across and can sweep across an area of Earth’s surface about 10,000 miles long.

Almost identical eclipses occur after 18 years and 11 days. This period of 223 synodic months is called a saros.

During a total solar eclipse, conditions in the path of totality can change quickly. Air temperatures drop and the immediate area becomes dark.

If any planets are in the sky at the time of a total solar eclipse, they can be seen as points of light.

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What Is A Comet?

A comet is a very small solar system body made mostly of ices mixed with smaller amounts of dust and rock. Most comets are no larger than a few kilometres across. The main body of the comet is called the nucleus, and it can contain water, methane, nitrogen and other ices.

When a comet is heated by the Sun, its ices begin to sublimate (similar to the way dry ice “fizzes” when you leave it in sunlight). The mixture of ice crystals and dust blows away from the comet nucleus in the solar wind, creating a pair of tails. The dust tail is what we normally see when we view comets from Earth.

A plasma tail also forms when molecules of gas are “excited” by interaction with the solar wind. The plasma tail is not normally seen with the naked eye, but can be imaged. Comets normally orbit the Sun, and have their origins in the Oort Cloud and Kuiper Belt regions of the outer solar system.

Comet Naming

Comets come in several categories. The most common are periodic and non-periodic.

In the past, comets were named for their discoverers, such as Comet Halley for Sir Edmond Halley. In modern times, comet names are governed by rules set forth by the International Astronomical Union (IAU). A comet is given an official designation, and can also be identified by the last names of up to three independent discoverers.

Here’s how it works. Once a comet has been confirmed, the following naming rules are followed. First, if the comet is a periodic comet, then it is indicated with a P/ followed by the year of its discovery, a letter indicating the half-month in which it was discovered, followed by a number indicating its order of discovery. So, for example, the second periodic comet found in the first half of January, 2015 would be called P/2015 A2.

A non-periodic comet would be indicated with a C/ followed by the year of its discovery, a letter indicating the half-month in which it was discovered, followed by a number indicating its order of discovery.

If a comet is independently discovered by three people named Smith, Jones, and Petersen, it could also be called Comet Smith-Jones-Petersen, in addition to its formal designation. Today, many comets are found through automated instrument searches, and so the formal designations are more commonly used.

Famous Comets

Well-known comets include the non-periodic comets Hale-Bopp (C/1995 O1), Hyakutake (C/1996 B2), McNaught (C2006 P1), and Lovejoy (C/2011 W3). These flared brightly in our skies and then faded into obscurity.

In addition, Comet Shoemaker-Levy 9 (D/1993 F2) was spotted after it had broken up after a close call with Jupiter. (The D in its proper designation means it has disappeared or is determined to no longer exist). More than a year later, the pieces of the comet crashed into Jupiter.

The periodic Comet Halley (1P/Halley) is the most famous in history. It returns to the inner solar system once every 76 years. Other well-known periodic comets include 2P/Encke, which appears ever 3.3 years and 9P/Tempel (Tempel 2), which was visited by the Deep Impact and Stardust probes, and makes perihelion around the Sun every 5.5 years.

Facts About Comets

There are many misconceptions about comets, which are simply pieces of solar system ices travelling in orbit around the Sun. Here are some fascinating and true facts about comets.

*The nucleus of a comet is made of ice and can be as small as a few meters across to giant boulders a few kilometres across.

*The closest point in a comet’s orbit to the Sun is called “perihelion”. The most distant point is called “aphelion”.

*As a comet gets closer to the Sun, it begins to experience heat. That causes some of its ices to sublimate (similar to dry ice sizzling in sunlight). If the ice is close to the comet’s surface, it may form a small “jet” of material spewing out from the comet like a mini-geyser.

*Material streams from comets and populates the comet’s orbit. If Earth (or another planet) happens to move through that stream, those particles fall to Earth as meteor showers.

*As a comet gets close to the Sun, it loses some of its mass due to the sublimation. If a comet goes around enough times, it will eventually break up. Comets also break up if they come TOO close to the Sun or another planet in their orbits.

*Comets are usually made of frozen water and supercold methane, ammonia and carbon dioxide ices. Those are mixed with rock, dust, and other metallic bits of solar system debris.

*Comets have two tails: a dust tail (which you can see with the naked eye) and a plasma tail, which is easily photographed but difficult to see with your eyes.

*Comet orbits are usually elliptical.

*Many comets formed in the Oort Cloud and Kuiper Belts, two of the outermost regions of the solar system.

*Comets are not spaceships or alien bases. They are fascinating bits of solar system material that date back to the formation of the Sun and planets.

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