- The Sun in the center of our solar system is a star.
- There are around 200 billion stars in the Milky Way alone.
- VY Canis Majoris is the largest known star in our galaxy, if this star was in the center of our solar system it would reach the orbit of Saturn.
- One of the smallest known stars in the galaxy is VB 10, it is only around 20% larger than Jupiter.
- Some large stars may only exist for a few million years while very small stars can exist for trillions of years.
- The lifespan of our own star, the Sun, is around 10 billion years.
- Supernovas are explosions generated by large stars when they come to the end of their lifespan.
- There are only around 2,500 stars visible to the naked eye at any one time in the night sky.
- The nearest star to our solar system is Proxima Centauri which is 4.2 light years away.
- The Sun is part of a single star system but there are also binary and multiple stars where 2 or more stars orbit around each other.
The Birth of StarsStars are born inside clouds of gas and dust known as nebulas which exist throughout the galaxy. Some nebulas form from the gravitational collapse of gas in the interstellar medium while others are the result of the death throws of a massive star. Hydrogen clumps together inside these clouds of gas growing ever larger and hotter until eventually the early stage of a star called a Protostar is formed. As gravity collapses the Protostar even more, temperatures in its core become hot enough
to trigger nuclear fusion. The star is now fusing hydrogen atoms together in its core creating an enormous amount of energy. The star is now in the stage known as its main sequence and depending on its size could remain in this state for billions or possibly even trillions of years.
Our nearest starA close up image of a star, our very own Sun.
SiriusSirius is the brightest star in the night sky.
When a star is in its main sequence it is fusing hydrogen atoms in its core which creates energy. The sun is an example of such a star, all stars will spend the majority of their lifespan in this state before they exhaust their supply of hydrogen. After this stage most stars become giants, for example when our sun can no longer fuse hydrogen in its core it will begin to fuse hydrogen in its outer shell causing it to expand greatly and become a red giant. The color of a main sequence star depends on its surface temperature, which is usually related to its mass. Low mass stars generally have a lower surface temperature and appear red, high mass stars generally have higher surface temperatures and appear blue. It’s worth noting that all stars emit light from every color of the spectrum but will appear as one color to us. Stars are classified with a letter depending on their surface temperatures, either A, B, F, G, K, M, or O. They are not in alphabetical order, stars with similar surface temperatures to our sun are classified as G, whereas a much hotter star may be classified as B or O.These are by far the most common type of star in our galaxy. Red Dwarfs have less than 50% the mass of our own Sun, as a result they are much cooler and emit far less energy. As Red Dwarfs burn their fuel at a very slow rate their lifespan is much longer than those of other stars, existing for hundreds of billions of years and possibly even trillions of years. Some red dwarfs with a high enough mass may become giants but will never achieve core temperatures high enough to begin fusing helium. Red dwarfs are classified with the letter M.Orange dwarfs are also very common in our galaxy, they generally have a mass of between 0.5 and 0.8 of the sun and have lower surface temperatures. Orange dwarfs stay in the main sequence period of their lifespan up to three times longer than yellow dwarfs such as our sun. As a result orange dwarf systems are considered very stable environments for the development of planets and the evolutionary process of life. Orange dwarfs are classified with the letter K.The Sun in the center of our solar system is a Yellow Dwarf, these are stars that have approximately between 0.8 to 1.2 the mass of our sun. The name Yellow Dwarf is rather misleading, firstly our sun only appears yellow due to the light interacting with Earth’s atmosphere, it is in fact white as is the case with the majority of Yellow Dwarfs. Secondly even though our sun is referred to as a ‘dwarf’ it is in fact larger in mass that the vast majority of stars in our galaxy. The lifespan of a Yellow Dwarf in its main sequence is around 10 billion years. Yellow-White dwarfs have a mass of approximately between 1.2 and 1.4 times that of the sun and have slightly higher surface temperatures. The stellar classification for Yellow Dwarfs is G whereas Yellow-White Dwarfs are classified as F type stars.Stars which appear white or whitish-blue generally have a mass approximately between 1.4 and twice that of the sun. Their surface temperatures can be almost twice as high as the sun and they are usually classified as A type stars. Blue stars generally have a mass of more than twice that of the sun, in some cases they can have a mass of more than a hundred times that of the sun with surface temperatures up to 10 times hotter and thousands of times brighter. Blue stars burn through their fuel at a far quicker rate than smaller stars meaning they have a lifespan of only a few million years, they are generally classified as B or O type stars.
Pleiades or Seven Sisters star cluster
Eruptions on the surface of a star, our Sun
The red supergiant Betelgeuse (Hubble image)