Our home-the universe we were born in!
It seems that we are the lost children of the cosmos, who have been engulfed by a world of their own! Do we remember the last time we sat in the moonlight looking at the night sky, have we forgotten our hobby of counting the stars? There used to be times when the world down on the Earth used to be uninteresting, and people used to look up into the sky staring at the stars in amusement before they dosed off! ...before things changed...
So, let's reconnect ourselves to our origins and stop fretting about the problems and the confines we live in. We are the children of the cosmos, and the universe is our playground! Come, let's re-claim the lawns!!
The figure above is definitely not to scale and is a bit understated to accommodate the entire Solar system. The scale given at the bottom of the diagram is important.
Astronomical Unit (AU)
1 Astronomical Unit (AU) is the average distance of the Sun from the Earth (the exact distance keeps changing depending upon the time of the year) and is equal to about 1.496 x 1011meters.
This number can also be written as 1.496E11 meters in the scientific notation, so no need to get scared if you see that odd alphanumeric with the part after E denoting the power(exponent) of 10.
So, is our Solar System big?...or is our Sun a huge object?!...absolutely wrong!
As you can see in Figure-3, a "Hypergiant" star (these are not science-fiction by the way!) can have a radius of upto or even greater than 1AU (the mean distance between Sun and Earth). So, if our Sun had been a Hypergiant, then our Earth would have been nearly grazing its surface and boiling away if not worse!
Of the planets depicted in the figures above, the four next to the Sun are called Terrestrial planets as they are rocky. The outer planets are often called Gas Giants as they are big in size and are mostly made up of gas with some rock at the core. Pluto which once used to be our ninth planet is considered to be a Dwarf planet as it doesn't satisfy the conditions to be called a planet. More over, Pluto is not the only dwarf planet in our solar system, there are many others.
So, the eight planets as we know are not the only objects orbiting the star we think belongs to us! Actually there are a huge number of them as you can see in the animation below.
In simple terms, an H-R diagram or HRD plots each star on a graph plotting the star's brightness against its temperature (color).
Correlation between Temperature and Color in Layman's language
The color of light emitted by any object which gives off light as a consequence of its temperature is related to its temperature. The brighter the object, the higher will be the energy of surface particles of the object, the higher will be the frequency of light emitted by the object. Higher frequency means the part of visible spectrum towards blue. So, there are some stars which are extremely hot and burn blue!
So, in the HR diagram, the stars to the left are highly luminous meaning very bright, and they generally tend to be blue in color and have high surface-temperatures. Thus, these stars end up at the top-left corner. As, the temperature decreases, the color becomes more reddish and luminosity decreases, and such stars end up towards the bottom-right corner of the HR diagram.
This general sequence of stars forms the diagonal running from the top-left to the bottom-right of the diagram, and the stars lying on this diagonal are called the Main Sequence stars. Our Sun is one of the Main Sequence stars lying somewhere in the center of the HR diagram. The stars like our Sun lying in this sequence are the very normal stars which seem to be following the basic common-sense correlation between temperature and luminosity.
There are some stars though, which lie at the other two corners of this diagram which are special and peculiar. These are the Supergiants and the Dwarfs!
Well, that you can see for yourself!
As you can very clearly see in the diagram above, our Sun is perched nearly at the tip of one of its spiral arms at the periphery of the galaxy!
Important Facts
The size of our galaxy is several thousand light years (ly). One light year is the distance traveled by light in one year. So, 1ly = 9.45 x 1015 m = 9.45E15 m
So, as seen so far, we are in no way in the category of special in the usual sense, though that may partly be the reason why we are safe and secure. But, that safety is virtual. We may not even get to know before an object not yet known to scientists suddenly crashes into us, destroying us completely, or a star near us goes supernova due to some unexplained reasons. Anyways, it is important to know that even if we survive the climate change, and global warming on this Earth (which we all most certainly wouldn't!), after about 5 billion years, the Sun will explode and expand to the orbit of the Earth and may engulf the Earth...and after that, the Milky Way is basically a disc of gas and dust swirling into a black-hole at the center of our galaxy so, ....!
[Figure-7 | Illustration of the two gigantic X-ray/gamma-ray bubbles (blue-violet) of the Milky Way (center) | Source: Wikimedia Commons | Author: NASA Goddard Space Flight Center | Copyright: Public Domain ]
These gama ray and x-ray emissions are released when a black-hole devours matter!
So, eventually if the human-race is to survive, we'll have to move out and away from our planet establishing bases elsewhere, colonizing other planets and exploring places beyond our present-day boundaries! So, why not start preparing from now itself!!
[Figure-7 | Source: Wikimedia Commons | Author: NASA | Copyright: Public Domain]
Here is a vision for habitats published by NASA from CASE FOR MARS from the 1980s, featuring the re-use of landing vehicles, in-situ soil use for enhanced radiation shielding, and green houses. A bay for a mars rover is also visible.
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