As we have seen in the last section the inward gravitational pull of the material is balanced by the outward radiation pressure to make a star stable. However, when the nuclear fuel inside the star is depleted the inward gravitational pull takes over and the star comes to a collapse state. The star forms a white dwarf when the mass is enough to be balanced by the degeneracy pressure of the electron. But what is the fate of the star when the mass is high enough not to be balanced by the electron’s degeneracy pressure?
The star collapses further, and a stage is reached where the electrons and protons combine to form neutrons and neutrinos. Again according to Pauli’s exclusion principle no two neutrons (fermions) can be in the same quantum mechanical state. The collapse enforces these neutrons to follow Pauli’s exclusion principle. Now, at this stage the neutrons become degenerate. . Now it is these degenerate neutrons that balance the inward gravitational pull. These degenerate neutrons maintain equilibrium with the gravitational inward pull. Such stars are called as neutron stars.
The size of neutron star is around the size of a city around a radius of 10km. The density of a neutron star is around 1017 kg/m3. The magnetic field of a neutron star is 1012 Gauss. Some neutron stars do spin around their axis and they are known as pulsars. They spin around at a speed of about 600 rotations per sec
In 1934, Walter Baade and Fritz Zwicky proposed the concept of neutron star. In 1965, Antony Hewish and Samuel Okoye discovered an unusual source of high radio brightness temperature in the Crab Nebula. Finally, in 1967, Jocelyn Bell and Antony Hewish discovered regular radio pulses from CP1919.
The first direct observation of a neutron star in visible light. The neutron star is RX J185635-3754 (Wikipedia.org)
As we have seen in the last section, the inward gravitational pull of the material is balanced by the outward radiation pressure to make a star stable. However, when the nuclear fuel inside the star is depleted the inward gravitational pull takes over and the star comes to a collapse state.
The star collapses, and a stage is reached where the electrons balances the inward gravitational pull. According to Pauli’s exclusion principle no two fermions can be in the same quantum mechanical state. The collapse enforces these electrons (fermions) to follow Pauli’s exclusion principle. Now, at this stage the electrons become degenerate. These degenerate electrons maintain equilibrium with the gravitational inward pull. Such stars are called as white dwarfs.
The size of white dwarf is around the size of Earth. The density of a white dwarf star is around 109 kg/m3 a million times denser than water. The temperature of a white dwarf is around 30,000K.
Above Fig shows a structure of a white dwarf (Image credit: cse.ssl.berkeley.edu)
On a clear moonless night in countryside when one looks up in the sky thousands of twinkling objects are seen called as stars. But what is a star? Probably this question must have baffled mankind for ages. Scientifically a star is a ball of hydrogen and helium gas having enough amounts to start a nuclear fusion. Nuclear fusion is a process where 4 hydrogen atoms are fused to form helium. The amount of energy released in the process is in form of heat and light.
4 hydrogen atoms getting fused into a helium nuclei and the energy released in the process. Image courtesy: opencourse.info
How a star is stable?
As the energy is released it causes a radiation pressure directed outwards and at the same time since there are large amounts of hydrogen and helium gas which causes inward gravitational collapse. When these two forces balance each other, equilibrium is established called as hydrostatic equilibrium and the star become stable.
The thermal radiation pressure and the gravity balance each other to make a star stable Image courtesy: www.schoolphysics.co.uk
NASA’s Infrared Observatory Measures Expansion of Universe
NASA’s Infrared Observatory Measures Expansion of Universe " H0 is around 74 +/- 0.4 (statistical) km/(s Mpc ) "
Spitzer Telescope
Astronomer Edwin, P. Hubble in 1920’s confirmed our Universe has been expanding. Astronomers invested lot of effort to understand this expansion rate whether its speeding up or speeding down or remaining constant. In late 1990’s they found the expansion is speeding up. Saul Perlmutter, Brian Schmidt, and Adam Riess in 2011 were awarded Nobel Prize in Physics for their work on demonstrating positive acceleration of the expansion rate using Supernova data.
The next immediate question is to find the expansion rate. The parameter H0 known as Hubble constant gives us the expansion rate of the Universe. For most of the half of 20th century the value of H0 was believed to be around 50 – 90 km/(s Mpc ). Data from Hubble Space Telescope, WMAP, Chandra X-ray Observatory, etc led us to conclude that the value of H0 to be around 70 – 77 km/(s Mpc ) a much more precise value reducing the uncertainty.
" What goes up… must come down " Leaving our Cradle Part - 2
- Vikram S.Virulkar
In the earlier part of the series we discussed the beginnings of the Rockets and some early pioneers like Tsiolkovsky, Goddard and Oberth. We continue exactly where we left off, about the new refined rockets and the arch enemy of a Rocket; Gravity.
So what is this gravity? And how does it affect us? We can’t see it but we have felt it every single moment from the time we were born, it keeps our feet planted firmly on the Earth and prevents our precious Atmosphere from dissipating away into Space. Now to understand the force of gravity in depth one might attempt to seek out a true giant of science; Sir Isaac Newton. For any mildly educated person, the very mention of the word gravity brings back a picture of Newton sitting under a tree and an Apple falling on top of him, igniting his curiosity about Gravity and the rest as they say is history.
Newton considers gravity as he observes the moon and falling apple peter lloyd
Although in some versions of the story, he merely saw an apple fall down, Nevertheless we owe our first attempt to understanding Gravity to the juicy fruit most of us relish. Newton started working on developing the laws of Gravity or the laws of attraction between two bodies in the Universe; He has stated detailed findings in his published work Principia (the book by Sir Isaac Newton).
“The earth is the cradle of humankind, but one cannot live in the cradle forever." - Tsiolkovsky Leaving Our Cradle Part - 1
- Vikram S.Virulkar.
For some of you, these words might have brought back a dim a memory of a famous quote by Konstantin Tsiolkovsky the Russian Pioneer who was instrumental in many ways for modern rockets and what he really said was, “The earth is the cradle of humankind, but one cannot live in the cradle forever."He compared our planet to an enormous cradle; I cannot help but term these words as Visionary. I feel compelled to agree with him.
To some, the meaning of these words is purely metaphorical but to others it is a picture of untainted reality, and it is ,perhaps in accepting this very truth, are we filled with a courage, that inspires us to leave the very cradle we were born in and walk on our two feet as human beings.
We cannot turn a blind eye to what lies in front of us as a species, we will one day leave this planet behind and roam the Cosmos, It is our destiny, if we don’t destroy ourselves first. This series takes a look at some of those attempts by us to leave that cradle, both as a race encompassing all mankind and as a country ravaged by its own problems, but chose to look up to the heavens.
The most critical part of buying a telescope isn't how much it costs or what kind of telescope it is, far more important is knowing which one you need and where are you going to use it.
But before we plunge into that, let me clear things up with a practical example
I own a 6 inch Celestron Nexstar series fully go-to SCT (Schmidt-Cassegrain Telescope), do I like it? Of-course I do, but for a completely different reason. The nature of my work demands a lot of frequent traveling to various parts of the country. I hold Astronomy Workshops in Schools and Colleges where I typically have a audience of 100-135 curious students. These students are eventually introduced to the heavens. The tracking option of my telescope makes it easier for me, I can concentrate on interacting with the Students rather than giving any thought to re-adjusting the telescope , plus the SCT saves me valuable space, weight and money(If you fly often , a large and ultimately heavy scope would be very costly to transport). When I start my observing sessions, I can set-up in 7-10 minutes, identify a planet and activate the tracking, the only time I would go back to the telescope is when it requires a change of target.(or more often when someone accidentally bumps the telescope, requiring a re-align).
If I was not doing the work I do, would I buy the same telescope? Absolutely not, for the price I bought my SCT (around 1.30 lakhs at he time), I could have bought a Reflector more than double its size and still have money to spare for accessories. So everything depends upon your use and how you can efficiently manage your telescope time
Dear Readers, we have, up till now seen the two major forces in the telescope market, Refractors- for their impeccable optical quality Reflectors- for their sizes and comparative reduction in price. But there is a third and more practical (but a little more expensive) option available in the market and for those of you who are guessing, the third option is the Schmidt Cassegrain Telescope (SCT) and the Maksutov-Cassegrain Telescope (MCT) these types are also called the catadioptric telescopes . The two types are famed for their optical quality and unmatched portability. The Two telescopes work on a folded light pattern, This is easier to explain with the diagram provided.
The SCT is in many ways a revolution in the field of amateur astronomy. However these technological marvels are quite basically a reflecting telescope but its easier said than done, the telescopes collect light just like any other mirror and then it is reflected to the secondary mirror which is attached to a corrector plate but this is where the beauty of the design comes into play, the light is not directed sideways, but back towards the mirror to a carefully placed opening in the middle, where the eyepiece lens is attached, this is called the visual back of the telescope. This innovation increases the focal length of the telescope and allows us to use a larger lens with a seemingly small tube. Astronomers around the worlds can use this design thanks to the efforts of James Baker, who invented this telescope working on a model of Bernard Schmidt’s original Schmidt Camera.
In the Last part of the series, we looked at Refractor telescopes. In this part we put the spotlight on the Reflector Telescope. In most people’s opinion, the Reflector telescope is nothing less than a boon to modern amateur Astronomy; I would list two main reasons of why reflectors sometimes score over refractors in the field of Amateur Astronomy.
Let’s look at the history of reflector telescopes. As we all have made note of from previous parts, Galileo was the first person to look at the heavens with a telescope of his own handiwork, we have all seen telescope evolve from that period, although it should not surprise the reader that the idea, that someone could use mirrors instead of lenses was probably older than the invention of the telescope, but after the invention of the telescope, the idea of replacing the lens with the mirror, slowly but steadily started to brew in the intelligentsia of the scientific community, more so with those closely related with Astronomy. The answer eluded most, for long, people tried various experiments with mirrors and the results were mostly unsatisfactory, until it was the great Isaac Newton, the father of Physics and the inventor of the Calculus who came to their rescue with the World’s first completely working model of the Reflecting telescope.
Newton
It is to him, that we credit the construction of the Reflecting Telescope, and rightly christen the design as the “Newtonian Reflector”( Although in terms of scientific accuracy, it is duly noted that he did not come up with the idea on his own, but brought into existence a instrument no doubt, though persistent efforts and gave the world a gift, one of the many he has given. Why he was interested and what prompted him to build this contraption is a story for another time). The design of the Newtonian was so simple yet so elegant that it was a overnight success. Suddenly mirrors could be used instead of expensive lenses and the size of the telescopes could grow, in turn gathering more light than ever before, gone were the days of the small handheld telescopes using lenses, it is probably right to say that the Astronomers of the time were gripped with “aperture fever” (A feeling common among amateurs who have grown out of their relatively small telescope and want a larger telescope to see more of the heavens).
In this part of the series, we take a look at the different types of telescopes readily and cheaply available (mind you, cheap is only a relative term) in the market today.
Note- Focal length is nothing but the distance that from the lens to the convergence point.
The F-ratio of the telescopes is calculated as the focal length of the lens divided by aperture of the lens (the size of the objective lens or mirror in your telescope).
F.O.V(Field of View) is quite simply how much area you are seeing at any point
The Focal length and the F/ratio play a vital role in the use of a telescope, it is very important you know what they mean.
The F-ratio varies in classification from “fast” to “slow”, a fast f/ratio means the image will be brighter and will give a wide field of view, the Fast f/ratio’sup to f/6 provide great wide field views. Faint nebulas and Star Clusters which are spread across a large area are much better rendered, but there is one shortcoming, the magnification is not the greatest, if you have other viewing interests, the telescopes with f-ratios of f/10 and above are best for planetary viewing and looking at binary stars. The Telescopes between f/6 and f/10 are a middle route that most tend to take if you are not really interested in the details of it all. Many hobbyists keep multiple telescopes for this very reason.
The Eyepieces
The eyepiece can be called the heart of the telescope, for without the eyepiece, the Telescope is quite useless. Having mentioned that, you need to know what type to buy and which one, there are plenty of options. The first thing to remember about the Eyepiece is, the lower the focal length of the Eyepiece, the higher the magnification you are going to achieve. The Magnification can be very simply calculated, simply divide the focal length of the telescope by the focal length of the eyepiece. For example, if the Focal Length of the Telescope is 1500mm and the focal length of the eyepiece is 25mm, the magnification will be 1500 / 25 = 60x, but I have to disappoint you at this point by saying the earlier statement does not mean that if you use a 1 mm eyepiece with a telescope of focal length 1500mm, you will get 1500x of magnification. There is a limit on every telescope called the magnification threshold; it is roughly 60 x per inch of aperture. For example, I use a 6 inch Schmidt-Cassegrain Telescope, the Magnification threshold of my telescope is 6 x 60 = 360x. This means for all practical purposes, I cannot “bump up” the Magnification beyond 360 x and get a good, clean image.
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