Skip to main content

You too can measure a star!!


Study of STARS

            How do you measure the size of a star? How do you estimate it’s mass? How do you know hoe distant it is? When you are asked how distant is place-A from place-B (assuming these two places are on Earth), you same some x km. When you are asked, how do you know that, you try to say that I measured it when I traveled by bike or you can say any measuring technique including Geo-mapping. But, you have never been to a star, nor did any machine, nor anything that we know. Still, how are we so certain about the parameters of a star? Read on to find out...

DISTANCE AND LUMINOSITY:

            When you look at a star, what you see is the apparent brightness of a star rather than its absolute brightness. This apparent brightness is measured in terms of magnitude. The scale is same as that of old catalogs which assigned 1st magnitude to the brightest and sixth magnitude to the just visible. At any point, a given difference in magnitude corresponds to definite ratio in brightness. Suppose, some star X is 5 magnitude times brighter star Y, it is said to be 100 times brighter than star Y. If any star is brighter than 1st magnitude, a negative value is assigned to it. For example, Sirius has -1.52 and Sun has -26.72 magnitude of brightness.
 Sun is apparently bright, but not brighter than many other stars which are very distant.
            What is the brightest star in the sky? Well, it depends on whether you are talking about absolute or apparent brightness. Sun is apparently bright, but not brighter than many other stars which are very distant. As they are very far, the light is getting faded and absolute brightness cannot be seen as such. 
HertzsprungRussel diagram can be used to classify stars based on their luminosity and temperature.
            Enough about brightness! How to measure the distance of star from earth? We will discuss the popular method of parallax, using which we can find the distance of about 4000 stars which are not too far from earth.  
Parallax is a method used to determine the distance to the closest stars. This technique for measuring astronomical distances is very important because it is a geometric method and independent of the object being observed. The principal of parallax can easily be demonstrated by holding your finger up at arm’s length. Close one eye, then the other and notice how your finger appears to move in relation to the background. This occurs because each eye sees a slightly different view because they are separated be a few inches.
If you measure the distance between your eyes and the distance your finger appears to move, then you can calculate the length of your arm. This same principal can be used on a larger scale to calculate the distance to an object in the sky, only we use different points on the Earth’s orbit instead of looking through alternate eyes. Calculating parallax requires that the objects right ascension and declination be recorded accurately so that we know the objects precise location on the celestial sphere.

TEMPERATURE, SIZE and MASS:

Now that we know the distance, apparent brightness (as seen by the naked eye) we can find the absolute magnitude by fixing a standard distance at which it is defined. It is chosen to be 10 parsecs. (Parsec=parallax + seconds).Parsec precisely means the distance at which a star makes one second parallax. i.e., 1/1296000 part of a circle. At this distance, sun has 4.86 magnitudes.
Parsec precisely means the distance at which a star makes one second parallax
As we can observe the color of the star can be seen, we can find out its temperature. Once the temperature is known, intensity of radiation can be found out as it varies as the fourth power of temperature. Absolute magnitude found out earlier is used to find how much energy is being emitted per square unit per second. The ratio of these two gives the surface area of the star and hence we can find diameter of the star.
Mass of the start can be found out, in most cases, only when there is any significantly large heavenly body in the vicinity. The mass of the star varies in direct proportion with the absolute magnitude. This is also called mass-luminosity law.
Now that you know how we can find the details of a star which is demonically distant.






Comments

Post a Comment

Popular posts from this blog

SAGA OF COLORS

SAGA OF COLORS             Speaking of colors is not as simple as it seems! It intertwines physics of light , the physiology of vision and our psychological perceptions . Colors have been used in psychology for mental and physical healing. They have been used across almost all cultures and countries to represent certain beliefs and ideas. For example: Indians consider white as the color representing peace, saffron for sacrifice, green for happiness and likewise red has been considered as the color for danger all over the world and hence it is used in painting danger boards, important instructions that are not supposed to be missed etc., Although many such things are formulated based on aesthetic appeal made by the color, some have scientific explanations too, which I will be covering in this article. Similarly, we will also discuss the role of colors in science, entertainment, psychology, photography, art. Colors intertwines physics of light, ph
1 comment
Read more

Small Town Data Business

All softwares are available here.. If you are living in a town, then chances are that you would have seen it quite often at several internet shops. Not just this. Mobile ringtones, songs are downloaded here.. And by the above sentence, they are trying to tell you that, downloads, are something different from regular browsing and that you might have to pay for them, if you want any. And what about the charges ? Almost as much as Apple Inc. is charging for (in many places). And what about the Quality and Genuineness? Not a bit. What's more? The people who work there will try to convince you that, the content that they are trying to sell you, is 100% Original, and only they are doing it for the lowest prices in the town, and might even add an extra clause saying, 'This content is very rare'. To conversation between such an Internet Shop owner and a customer (who apparently do not know much about internet) goes somewhat like this. Customer : I have a mobile phone. I w
1 comment
Read more

PERSEVERANCE

Perseverance - One Word. If you randomly pick 10 quotations on SUCCESS, majority would be having this word. This little word means, to never give up. Perseverance, as such needs some little introduction. We persevere when we are inspired. We all need inspiration. If you are all like me, we seek inspiration from outside. Some seek it in academicians, some in social heroes, some in even fictional characters. And this inspiration that we get, unfortunately, lasts for a small amount of time. Just like when we take bath to keep us clean from germs, it only lasts for a period of time, after which we take bath again. Inspiration, as such should be constantly fed into our brains, just to be sure that we are always charged. I personally like Swami Vivekananda. I was inspired by his words. Who wouldn't? I took him as inspiration during my childhood. It so happened that, I thought I need inspiration from a new person. So, I searched. This time, I wanted to choose a person as good as, if
1 comment
Read more