The Sun – that incredibly bright glowing orb in the sky that most of us take for granted. We may glance at it ever so briefly so as not to hurt our eyes, and then go about our business forgetting about it. Or it may even irritate us when it gets in our eyes while driving. But without the Sun, there would be no life on Earth of any kind, no people, no animals, not even insects – nothing. The Earth would be only a huge frozen ball drifting through the blackness and empty void of space with terribly cold temperatures; if not absolute zero(-459.67 degrees Fahrenheit), then pretty close to it. You see, the Sun is the Earths best friend; it is the foundation of all life on Earth. Ancient civilizations seemed to understand this since a number of them, including the ancient Egyptians and Romans, even worshipped the Sun as a god and planned celebrations around it. The Sun was called Sol by the ancient Romans, in effect the Roman Sun God. Even the name of our Solar System is derived from the name Sol;
The Sun, roughly 4.6 billion years old, is located at the center of our Solar System at a mean distance from Earth of about 93 million miles. This means that light from the Sun takes roughly 8 minutes and 19 seconds to travel this distance to the Earth – the speed of light in a vacuum is 186282 miles per second. It forms a sphere of plasma with a diameter of 864938 miles and a circumference of 2.718 million miles(109 times that of the Earth) which, due to internal convection currents, generates a very strong magnetic field. The temperature of the Sun will vary from about 10800 degrees Fahrenheit at its surface to around 27 million degrees Fahrenheit in the inner core, which is at a pressure of 330 to 360 gigapascals; this is roughly equivalent to 250 billion times the Earths atmospheric pressure at sea level. The surface area of the Sun is about 2.38 trillion square miles compared to 200 square miles for the Earth, about 1190 times as much. Its volume is approximately 877.4 quadrillion cubic miles, which is about 1.3 million times that of the Earth – roughly 1.3 million Earths could fit inside the Sun! With an estimated mass of 4.18 nonillion pounds, the sun is about 332946 times the mass of the Earth and 1048 times the mass of Jupiter – the Sun contains 99.8 percent the mass of the entire Solar System! With all this mass, the Sun’s surface gravity is approximately 27.94g, about 28.015 times that of Earth. Put another way, a 200-pound man on Earth would weigh 5603 pounds on the surface of the Sun if he could reach it – he would be vaporized long before then! It should be noted that with such a strong gravitational field the escape velocity from the
The Sun’s rotational speed varies according to latitude since the Sun is a gaseous plasma and not solid. The fastest speed is at the equator where it is about 4467 miles per hour; the solar day is about 24.47 days, although this would vary some at different latitudes.
The Sun’s composition by mass according to our current knowledge of the Sun is as follows: hydrogen 73.46 percent, helium 24.85 percent, oxygen .77 percent, carbon .29 percent, iron .16 percent, neon .12 percent, nitrogen .09 percent, silicon .07 percent, magnesium .05 percent, sulfur .04 percent.
Located in the Orion Arm spiral of our Milky Way galaxy, the Sun – and the Solar System as a whole – orbits the galactic center at a velocity of around 492120 miles per hour at a mean distance of 167.8 quadrillion miles or about 27200 light-years. The Sun would make a complete revolution around the galactic center of the Milky Way approximately every 238 million years!
The Sun has 8 major planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune – and 3 minor, or dwarf, planets – Pluto, Eris, and Farout(2018VG18 – Farout is a nickname right now, not an official name). Mercury orbits the Sun every 88 days at a distance of 28.5 to 43.5 million miles. Venus orbits the Sun every 225 days at a distance of 66.78 to 67.69 million miles. Earth goes around the Sun every 365 days and has a mean distance of 93 million miles from the Sun in a nearly circular orbit. Mars revolves around the Sun every 687 days at a distance of 128.4 to 154.8 million miles. The next planet, Jupiter orbits the Sun every 11.6 years at a distance of 740.5 to 816.6 million miles. Saturn goes around the Sun every 29.5 years at a distance of 839 to 934 million miles. Uranus revolves around the Sun every 84 years at a distance of 1.7 to 1.89 billion miles. Finally, the last major planet, Neptune, orbits the Sun every 164.8 years at a distance of 2.77 to 2.82 billion miles. Pluto, Eris, and
Pioneer 6, 7, 8, and 9 were the first space probes designed especially to observe the Sun in space outside the vicinity of the Earth. They were put into orbit around the Sun at a distance similar to the Earth’s orbit around the Sun(93 million miles) and were able to obtain measurements of the solar wind and magnetic field which significantly increased our knowledge of the Sun. Pioneer 9 lasted longer than any of the other Pioneer space probes, transmitting information about the Sun until May 1983.
In the 1970s the Skylab mission made important observations of the transition region of the Sun and of ultraviolet emissions of the solar corona – this included discoveries of coronal mass ejections and phenomena known as coronal holes which are areas of the corona which are dark because of relatively cooler temperatures than the surrounding area. Also in this time period, Helios-A and Helios-B, a joint project of the U.S.A. and Germany, were launched inside the far point of Mercury’s orbit around the Sun(43.5 million miles) to make observations of the solar wind. These missions further increased our knowledge of the Sun.
The Solar Maximum Mission was launched by NASA into Earth orbit in 1980 to, as the name implies, study increased solar flare activity from the Sun. Unfortunately, there was an electronics failure within a few months causing the satellite to become useless. Then in 1984, the Space Shuttle Challenger(obviously before its tragic explosion on January 28th, 1986) was able to retrieve the satellite, repair it, and release it back into Earth orbit where it was able to take thousands of very important photos of the Sun’s corona before it’s orbit eventually decayed and it burned up in Earth’s atmosphere in June 1989.
In 1991 Japan launched it’s ‘Sunbeam’ satellite, Yohkoh, to observe solar flares in the x-ray wavelengths through a complete solar activity cycle of eleven years. It increased our understanding of solar flares and the Sun’s corona significantly – in particular that there are different types of solar flares and that the corona is very active even when solar flares are not present. It malfunctioned in 2001 and became useless, then burned up in the atmosphere upon reentry in 2005.
The Solar and Heliospheric Observatory(SOHO) was launched jointly by NASA and the European Space Agency on December 2nd, 1995 on a 2-year mission, although this was later extended to run through 2012. SOHO is situated in a Lagrangian between the Earth and Sun roughly 930000 miles from Earth, about 4 times the distance to the Moon. A Lagrangian point between the Earth and Sun is a distance where the gravitational pull of each is equal and cancels out. Later, in large part because SOHO has been so successful, the Solar Dynamics Observatory was launched in February 2010. Both solar space probes have been able to make constant observations of the Sun in a wide range of wavelengths and have discovered a number of comets.
The solar space probes mentioned so far have only studied the Sun in the ecliptic plane, that is mainly the Sun’s equatorial region. The Ulysses solar probe was launched in 1990 with a planned mission duration of over 18 and 1/2 years to specifically study the Sun’s polar regions in great detail. It traveled an unusual path since it first went by Jupiter to use its great gravitational pull to ‘slingshot’ it far above the ecliptic plane so it could orbit the Sun’s polar regions. It travels around the Sun every 6.2 years at a close approach of 125.55 million miles and a far distance of 502.2 million miles at an inclination of 79.11 degrees from the ecliptic plane(perpendicular to the ecliptic plane would be 90 degrees). Ulysses has made many important observations of the solar wind and magnetic field over the polar regions of the Sun.
The solar space probe Genisis was launched on August 8th, 2001 –
In October 2006 the Solar Terrestrial Relations Observatory(STEREO) was launched – this was actually two identical space probes launched into different orbits from each other which then enabled stereoscopic observations of the Sun, including coronal mass ejections, solar flares, and other phenomena, to be made.
How Hot Is The Sun?
The Sun’s temperature varies from 10800 degrees Fahrenheit at the surface to about 27000000 degrees Fahrenheit in the center. Even at 10800 degrees Fahrenheit, this is hot enough to turn any metal into a gaseous state. At the extreme temperature and pressure at the center of the Sun, matter exists in a plasma state where all the electrons are stripped away from the nuclei of the atoms and proton-proton fusion takes place. That is, the nuclei of hydrogen, which is a single proton, fuse with each other in this plasma state. In some ways, the process of fusion in the Sun could be thought of as a controlled thermonuclear explosion, where in this case it is stabilized by the massive force of the Sun’s gravity. Also because the Sun is so incredibly massive, as explained previously, it will take billions of years for it to completely exhaust the supply of hydrogen fuel sustaining this fusion reaction.
How Big Is The Sun?
The Sun is incredibly large and massive compared to the Earth. By volume, it is 1.3 million times the size of the Earth – that is, 1.3 million Earths could fit inside the Sun! It’s surface area is 1190 times that of Earth and the Sun is 332946 times as massive as Earth and 1048 times as massive as Jupiter. In fact, the Sun contains 99.8 percent of the mass of the entire Solar System!
How Old Is The Sun?
The most up to date research indicates that the Sun is about 4.6 billion years old. This has been largely determined by the remarkable fact that the Sun has oscillating pressure waves caused by the enormous and violent pressures and perturbations deep within the Sun. Scientists have calculated the vibrational frequency expected for the Sun at different stages of its life and by greatly compressing these oscillating vibrational frequencies and a process of extrapolation have calculated to a great degree of accuracy how old the sun is.
How Far Away Is The Sun?
The Sun has a mean distance from the Earth of about 93 million miles. The Earths orbit around the Sun is nearly circular, with only a slight eccentricity of .01671 – the Earth’s closest approach to the Sun is about 91.4 million miles and its farthest distance is roughly 94.5 million miles.
How Bright Is The Sun?
The Sun seems so bright on a sunny day that we can scarcely look at it for any length of time – we must glance quickly away. And we certainly wouldn’t want to since it would be very dangerous to do so. But in scientific terms, just how bright is the Sun anyway? Now here we will be talking about the brightness of the Sun as we perceive it underneath the thick layer of the Earths atmosphere where its brightness is attenuated and most, although not all, ultraviolet rays are screened out. After all, just exposing bare skin to the sun on a midsummer day without any sun lotion or other protection can result in a very painful sunburn! As one increases their altitude and the atmosphere becomes progressively thinner, the Sun’s brightness will increase. Also, it will vary according to the tilt of the Earth in the various seasons and the time of the day – these all influence how much atmosphere the Sun’s rays have to travel through. In addition to these factors, the eccentricity of the Earth’s orbit(.01671) must also be taken into consideration.
Having said all this, bright sunlight has an illuminance of about 98000 lux, which is defined as lumens per square meter, on a flat surface at sea level. The average color temperature of the Sun is around 5500 degrees
The photosphere is the visible surface of the Sun and is anywhere from 10 to over 100 miles thick. When an image of the Sun is taken phenomena known as limb darkening occurs where the center of the image is darker than its edges. This is because the upper part of the photosphere is cooler than the lower part. The visible light we see from the Sun comes mostly from the layer above the photosphere as ionization occurs releasing visible light while the layer below the photosphere is mostly opaque to visible light.
The Sun’s atmosphere is made up of 4 main parts – the chromosphere, transition region, corona, and heliosphere. The chromosphere, transition region, and corona
There is a minimum temperature region that extends about 300 miles above the photosphere at a temperature of about 6900 to 7000 degrees Fahrenheit. The chromosphere is a layer about 1200 miles thick above the photosphere which gets its name because at the beginning and end of a total solar eclipse there is often a colored flash of light. There is a steady increase in temperature as one moves up in latitude through the chromosphere until a maximum temperature of 35000 to 36000 degrees Fahrenheit results at the top.
There is a thin layer of about 120 to 130 miles thick above the chromosphere called the transition region. As the name implies, there is a transition, or increase, in temperature from about 36000 degrees Fahrenheit to almost 1800000 degrees Fahrenheit. It should also be noted that there is not a distinct boundary of the transition layer, it is more of a tenous change.
The layer of the Sun’s atmosphere above the transition region is called the corona. The average temperature of the corona is somewhere between 1800000 degrees Fahrenheit and 3600000 degrees Fahrenheit, but in the very hottest regions is believed to go up to anywhere from 14000000 to 36000000 degrees Fahrenheit. Although the reasons for such hot temperatures are not well understood, it is believed that a process of magnetic reconnection, where magnetic energy is converted to kinetic energy in certain types of highly conducting plasma states, is at least partially responsible for this.
The outermost region and very tenuous region of the Sun above the corona region is called the heliosphere, which contains the solar wind which is in a plasma state. The solar wind itself travels through the heliosphere outward towards space and the rest of the Solar System until something called the heliopause occurs around 50 astronomical units(the mean distance from the Earth to the Sun) from the Sun, or about 4.65 billion miles away. Essentially, the heliopause is the theoretical boundary where the force of the solar wind in the heliosphere is balanced by the interstellar forces of surrounding stars and thus is unable to expand any further. So one might really think of the heliosphere as being a giant bubble with a radius of approximately 4.65 billion miles which contains the solar wind of the Sun.
The Sun has disturbances which result in incredibly violent storms, the effect of which can often be felt throughout the Solar System. Of course, there are a number of different types of storms on the Sun, some of which include geomagnetic storms, solar particle event, coronal mass ejection, coronal cloud, and solar flares.
Although commonly referred to as a solar storm, a geomagnetic storm is actually the interaction of the solar wind with the Earth’s magnetosphere. This solar wind shockwave is temporary in nature and can cause a compression of the Earth’s magnetosphere resulting in the transmission of energy through it which results in an increased plasma flow of charged particles that can cause an increase in electrical current. These geomagnetic storms can be violent and severe enough to cause widespread electrical outages.
Solar Particle Event
A solar particle event, also known as a proton storm, results when protons become accelerated because of a solar flare or a coronal mass ejection event and enter the Earth’s magnetosphere causing ionization of the ionosphere. The result can be similar to the phenomena of auroras, also called northern lights, occurring in the higher latitudes of the Earth’s atmosphere, the main difference being that an aurora is caused by an electron storm rather than protons.
Coronal Mass Ejection
A coronal mass ejection is when there is a large release of plasma along with the magnetic field that goes with it from the Sun’s corona. It is not uncommon for a coronal mass ejection to follow after a solar flare, where they then become part of the solar wind going out into the Solar System. During the solar maximum activity they are much more common, often occurring several times a day. When the Sun is at its minimum activity level, there may only be one about every week.
A coronal cloud is simply the cloud of hot plasma which surrounds a coronal mass ejection. Being made up of mostly protons and electrons, this cloud is the part of a coronal mass ejection that is most likely to reach the Earth, if the Earth is in its path and can cause very severe damage to different types of electrical equipment on Earth as well as satellites in orbit.
A solar flare, simply put, is a gigantic explosion in the Sun’s atmosphere. We will take a closer and more
When the Sun is being observed by scientists, sometimes a sudden flash of brightness will occur on the sun. This is actually a gigantic explosion on the Sun, commonly known as a solar flare. Solar flares can range from minor, which can barely be observed, to major ones which are very easily observed. Sometimes an especially powerful solar flare can also be accompanied by a coronal mass ejection, although this is not always the case. The strength of solar flares is actually rated by scientists in a power-law range of magnitudes.
Solar flare emissions consist of both particles and the radio wave portion of the electromagnetic spectrum – some high-energy particles can often reach near-light speeds and thus arrive at the Earth at almost, but not quite, the same time. The other portion of the plasma ejecta can take days to reach the Earth. These particles can cause ionization in the Earth’s ionosphere resulting in aurora(northern lights) and along with the radio wave emissions can severely disrupt radio communications. On July 23rd, 2012 there was an absolutely massive and extremely dangerous solar storm consisting of a solar flare, coronal mass ejection, and electromagnetic radiation that barely missed the Earth. Had this gigantic storm directly hit the Earth, the results could have been catastrophic. According to scientists, there is a very significant chance that another great solar storm similar to this one could hit the Earth in the near future!
The solar wind is an emission of charged particles in a plasma state which come from the upper part of the Sun’s atmosphere, the corona. A magnetic field is also part of the solar wind and travels along with it. Because of the very strong magnetic field within the corona, extremely hot temperatures are reached – these can vary anywhere from 1.8 million degrees Fahrenheit to 36 million degrees Fahrenheit. These super hot temperatures energize the particles, mostly protons and electrons, with some alpha particles, and give them the kinetic energy they need to escape the Sun’s gravity, between 500 and 10000 electron volts, and then move in the solar wind out into the solar system – remember the heliosphere containing the solar wind extends out to 4.65 billion miles, at which point what is known as the heliopause is reached; this is the outer boundary of the heliosphere. The heliopause can also be defined as the outer boundary of the heliosheath which is the region of the heliosphere where the solar wind comes into contact with the interstellar medium. Please note that the solar wind will not be uniform in density and temperature, this will all vary depending on the part of the Sun the particles emanate from and will also change with time as the solar wind intensity gradually dissipates into the solar system. Since these particles are being released in the solar wind in a non-uniform way in a 3-dimensional process from the outer atmosphere(corona) of the Sun, the intensity rate would be expected to decrease inversely proportional to the cube of the distance from the Sun. Time should also be a factor as the particles in the solar wind gradually lose kinetic energy. For example, the solar wind should still be quite intense reaching Earth, but far weaker at its outer limit when it reaches Pluto. The particles in the solar wind are ejected from the corona at a speed of about 900000 miles per hour and will vary between 558000 miles per hour and 1680000 miles per hour traveling through the solar system until reaching the heliopause, at which point they will lose even more kinetic energy from the compression forces of the interstellar medium and slow down greatly.
It should be noted that at the point the particles in the solar wind reach Earth, they are usually traveling around 670000 miles per hour. But if a coronal mass ejection occurs their speed can increase to 1116000 miles per hour and rarely during an especially large coronal mass ejection up to 2236000 miles per hour when they reach Earth. Something else that should be mentioned is that as the solar wind moves out through the solar system it is not a perfect sphere in shape at all, but is in fact very irregular due to a number of factors including its non-uniform emission from the Sun because of varying conditions on the Sun and contact with forces of the interstellar medium. The solar wind can give us the beautiful Aurora Borealis, northern lights in the northern hemisphere, or Aurora Australis, southern lights in the southern hemisphere. They can also cause problems with electrical equipment and devices on Earth and with satellites in orbit, as well as being very dangerous to astronauts, especially in higher-Earth orbit or deep space outside the protection of Earths magnetic field.
The Aurora Borealis and Aurora Australis are light phenomena which occur in the higher latitude regions, around the Arctic and Antarctic respectively. They happen when the charged particles from the Sun’s solar wind interact with the Earth’s magnetic field and cause ionization in the ionosphere region of the atmosphere. The main reason these Auroras occur mainly in the higher latitudes is because that is where the Earths magnetic field is the strongest – the higher latitudes are closer to Earths magnetic poles and so the magnetic field is closer to being perpendicular to the surface of the Earth and interacts more strongly with the particles. Aurora Borealis and Aurora Australis will be more intense during times of greater solar activity, such as coronal mass ejections, sunspots, and solar flares. For example, sometimes during especially intense solar activity, which maximizes and minimizes during an eleven-year cycle, the Aurora Borealis will even be visible in the northern states, although it will still be more brilliant farther north.
Solar energy consists of a wide spectrum of electromagnetic radiation which is continuously emitted from the Sun. This consists of ultraviolet and infrared(heat) at the lower end of the spectrum to x-rays, gamma rays, and even lower energy cosmic rays(still higher energy than gamma rays) at the higher end of the spectrum, with visible light in the middle. The Sun emits protons, electrons, and alpha particles which are basically 2 protons and 2 neutrons bound together into a nucleus identical to a helium-4 nucleus. An interesting side fact here is that the higher energy cosmic rays do not come from the Sun but are thought to come from supernovas and other unknown sources in our galaxy and other parts of the Universe.
The Sun produces roughly 380 billion quadrillion watts of power every second, more than enough for the entire human civilization on Earth! It does this by fusing four hydrogen nuclei together to make one helium nuclei in the plasma state(in a plasma state electrons are stripped away). Since the Sun has a mass of approximately 4409 quadrillion quadrillion pounds, the fusion reaction in the Sun is expected to last billions of years into the future.
The Sun produces a massive amount of a ghostly fermion particle called a neutrino – about 419.354 billion neutrinos pass through a square inch on the surface of the Earth every second. We call these ghostly particles because they have almost no interaction with matter; for a long time it was thought that neutrinos had no mass at all, but now we know now that they actually have a very tiny bit of mass. Although it still isn’t known what the exact mass of the neutrino is, scientists have made observations that seem to imply that it is less than one-millionth that of an electron. These particles interact so poorly with matter that they pass through the Earth as if it weren’t even there; the daylight side of the Earth has essentially the same number of neutrinos as the dark side. Another shocking fact is that in any given second there are roughly 100 trillion neutrinos passing through your body and you don’t even have a clue!
What causes neutrinos? Well, we really don’t have a precise answer yet, but based on current cosmological theoretical models it is thought that the production of neutrinos is a by-product of the fusion process in the Sun which is necessary to maintain a consistent gravitational constant. They actually seem to account for a very small amount of angular momentum that is left over in this fusion process – light and heat along with other parts of the electromagnetic spectrum carry about 97 percent of the energy produced by fusion away from the Sun, while neutrinos carry the other 3 percent.
Sunspots are temporary blemishes on the Sun’s photosphere, it’s outer shell, that appear as dark spots because of their reduced temperature compared to the surrounding region. This reduced temperature is caused by an increased intensity of the magnetic field flux in these areas which in turn inhibit convection currents, thus causing the cooler temperatures. The term ‘cooler temperatures’ is a relative one compared to the surrounding area since the actual temperature of a sunspot is about 7800 degrees Fahrenheit. The average sunspot is about as large as the Earth, although there is quite a bit of variance. Sunspots often occur in pairs because of the properties of magnetic polarity and their frequency on the Sun vary according to an eleven-year cycle, with a maximum and minimum number of sunspots every eleven years.
Sunspots actually move across the Sun lasting from a few days to a few months, but they will eventually diminish and disappear. Their size can vary from less than 10 miles to over 100000 miles across and they can appear individually or in groups. Some of the largest ones can actually be seen on the Sun without a telescope, but please do not attempt to observe this without adequate protection since permanent visual damage is likely to occur. Sunspots have even been observed on other stars, but they are called starspots, not sunspots.
A solar eclipse will occur when the Earth passes through the Moons shadow from the Sun; depending on the Moons distance from the Earth this will be either a partial or a total eclipse. Also, this only happens during a new moon when the Earth, Moon, and Sun are aligned in a straight three-dimensional line and the Moon is close to the ecliptic plane, which is the mean plane of the apparent path of the Sun through the Earths sky during one full year. Solar eclipses would occur much more often during the new moon except for the fact that the plane of the Moons orbit is tilted over five degrees from that of the plane of the Earths orbit around the Sun, so most of the time the Moons shadow misses the Earth completely during the new moon.
A total eclipse of the Sun is a very rare event and spectacular to behold, seemingly with almost supernatural qualities. Everything becomes so dark that it appears as though night has come and even stars become visible. Indeed, total eclipses were often very frightening to people and cultures of the past who witnessed them and they gave great spiritual and religious significance to them, sometimes believing that they were very bad omens. Total eclipses of the Sun are so rare because the timing during the new moon has to be much more exact than that of a partial solar eclipse. Not only that but when a total eclipse does occur it traces only a very narrow path on the Earth’s surface – only observers in that narrow range of the Moon’s shadow will be able to experience this strange and wonderful phenomenon. A total eclipse will only last for about 7.5 minutes in any given location; during this time it will become completely dark as the Moon completely obscures the Sun – only a thin ring of light, the solar corona, is visible around the Sun. Those observers outside this narrow path can still observe the partial eclipse for a much longer period of time as the Moon’s full shadow, the umbra crosses the surface of the Earth. A note of caution here – never observe any eclipse without adequate protection as permanent visual damage is likely to occur.
Is The Sun A Star?
Is the Sun a star? Well, the short answer is yes, of course. Many people may not know the distinction between the Sun and a star, but they are really one and the same. A Sun may be thought of as a star with a system of planetary bodies, but of course, many ‘stars’ have planets orbiting around them. So the next time you are outside and the Sun is shining, just try to realize that the Sun is a very close star that is the very foundation for all life on planet Earth.
What Type Of Star Is The Sun?
The Sun is a very average and rather indistinct star in our Milky Way Galaxy. To be more specific, it is classified as a type G yellow dwarf star – it can be difficult to believe that anything as massive as the Sun is considered a dwarf but in the classification system of stars that is the case. As mentioned earlier, the Sun actually has 98.6 percent of all the mass in our Solar System! The type of star the Sun is and its classification will change as it gets older with the passing billions of years, much as a persons appearance will drastically change as they get older.
When Will The Sun Die?
Yes, there will be a time when the Sun will come to an end, but that will be billions of years in the future. As we have discussed earlier, although the Sun consumes its hydrogen fuel at an incredibly rapid rate, it is so massive that it will take billions of years to exhaust its supply of hydrogen. Right now the Sun is middle-aged, considered a mid-sequence class G dwarf star; in the prime of its life.
The Sun started it’s life billions of years ago as a prototype star when it gradually condensed from a gigantic cloud of gas and dust. As the condensation continued over billions of years, gravitational forces caused the Sun to heat up and it started emitting light and other electromagnetic radiation. Then the Sun eventually started the process of nuclear fusion and became a main-sequence yellow dwarf star, which is what it is now. This stage can last up to 10 billion years – right now we are about halfway through this stage and so we can expect the Sun to remain a yellow dwarf about another 4 to 5 billion years. After this, the Sun will completely exhaust its hydrogen fuel and become very unstable – it will become what is known as a Red Giant star. This name comes from the fact that the Sun will expand to many times its current size, up to 250 times. The final stage of the Sun will be that of a white dwarf after the sun has expelled most of its mass into outer space, leaving behind only a hot stellar core which will gradually cool, and at some far, far, distant future time it will go dark forever until time itself runs out.