Measuring Cosmic distances

                                                   Functioning of the white dwarf

Distance to the nearest asteroid and some other cosmic distances can be measured simply with the help of radar.

Bigger distances depend upon spotting a blasting star in a distant galaxy, or measuring the expansion of space time itself.

A type 1a supernova has been found in a nearby galaxy called the M101- also called as the Pinwheel galaxy.

There are actually several kinds of supernova but the one of type 1a is not formed as a result of explosion of a huge star, but are formed as a result the destruction of a white dwarf around a younger binary partner, or two white dwarfs entering into one another. And in other cases, material is stripped from other partner until the matter reaches the ‘critical mass’ of the dwarf. As a result of this supernova arise.

Since decades supernova of this kind have been studied and we have learnt that their formation is quite predictable. For example, it is easy to accurately calculate the amount of energy they bring into universe by studying the variation of output energy they bring with change in time. Therefore they are very useful for measuring cosmic distances.

                                                                         Parallax

Going a step back, it is easy calculating cosmic distances within our solar system as we can get ounced radar signals from nearest planets and stars and knowing the speed of an electro magnetic signal and how long it takes for the signal to get to the objects and back again and we can get the distance within our solar system.

But on the other hand measuring the distance to the nearest star can be a little tricky.

If we send a radar signal to Proxima Centuari then it will take 4 yrs to go there and another 4 yrs to come back, but still the signal would be so weak that it will be impossible to detect it.

So for measuring such distances we use a technique called as the  'parallax'.

PARALLAX

The theory of parallax measurements is simple.Earth takes 1 yr to complete I revolution around sun, so we take the position of a nearby star in the sky for January for example, and then repeat the exercise six months later in July.

Earth will be at the extreme of its orbit, and so the nearby stars will be shifted little bit in the sky. From knowing the angular apparent movement of the star and the Earth’s diameter, we can calculate the distance to it.

STANDARD CANDLES

Standard candles are used for measurement of distance of more distant stars which cannot be measured by parallax.

Type 1a supernova, like the one in M101 is a type of standard candles – the amount of the enegy released by this supernova is believed to be the same, no m,atter where they are located in the cosmos.

                                                                 Standard candles
Both types of objects can be easily identified by the way their output of light varies over time and once they've been identified, it's easy to calculate the actual amount of energy, or light, that it should be giving out.

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