28 December 2007

Black Holes

If you had read my article on ‘The Life of the Star’, you would have known that a Black Hole is created when a huge and massive star (more than 2.5 times the mass of the sun) runs out of hydrogen and collapses into a Supernova explosion. If the core of the star remains the explosion it becomes a black hole. But what exactly is a Black Hole? Why is it different from other dead stars?

This image shows how a Black Hole may look like in the Milky Way.

When such a massive star is crushed into a smaller volume, the gravitational attraction of the star increases and hence the escape velocity. The gravitational attraction of a Black Hole is very high that it pulls out anything that is closer to it. The escape velocity of a Black Hole is more than the velocity of light i.e. an object in a Black Hole should travel faster than the speed of Light to escape the gravity of Black Hole. And hence even light cannot escape its gravity. Eventually nothing can escape out of a Black Hole as nothing can travel faster than light. This is the same reason that the Black Hole is invisible. You can only see an object when it reflects light. But since Black Hole does not reflect light it is invisible.

NOTE: None of the images of the Black Holes are real. They are artistic works to show how a Black Hole may look like. A Black Hole can not be photographed. It can only be detected.

There are three types of Black Holes – Stellar Black Holes, Supermassive Black Holes and Miniature Black Holes.

A Stellar Black Hole is a Black Hole created by a single star as explained above. It can be seen in almost every other galaxy.

This is an image of a Stellar Black Hole.
A Supermassive Black Hole is a Black Hole whose mass is between 105 and 1010 times the mass of the sun. It is known that most of the galaxies, including the Milky Way contains a Supermassive Black Hole in the center. It could have formed when a Stellar Black Hole start growing by pulling stars of huge mass by means of gravity. Supermassive Black Holes are only found in the center of the galaxy.

Image of a Supermassive Black Hole.
A Miniature Black Hole has not been identified but some theories say that Miniature Black Holes might have formed a short while after the Big Bang.

Questions may arise such as ‘How a Black Hole was discovered if it is invisible?’ and ‘Who discovered the first Black Hole?’ Here are the answers.

Before answering them let me explain about Binary Star System. A binary star system consists of two stars very close to each other and also moves around each other. Most of the stars we see in the night sky are binary stars though it looks like one twinkling star. Sirius, the brightest star in the sky is a binary star. Sirius A is bigger and brighter than Sirius B which can be seen only through a telescope. Sun, of course is a single star. Distance between two binary stars may be about 20 to 50 times the distance between Sun and Earth. But the distance between two single stars will be in Light years.

Image of Sirius A (bright one) and Sirius B (smaller one above it).

Consider a binary system of stars where one of the stars is a black hole and the other a normal star. If the normal star's envelope gets close enough to the black hole, then the fierce gravity of the black hole can rip out gas from the normal star which is then swallowed by the black hole.

However, due to the conservation of angular momentum, the gas cannot plunge straight into the black hole, but must orbit it for some time before it gets sucked. Thus, a disc like structure is formed around the black hole from which gas is pulled slowly into the black hole. When the gas orbits the black hole in the disc, its temperature is raised to several millions of degrees which emits radiation in the X-ray part of the spectrum (by the first note that I explained above). Thus, when we detect X-ray sources in the sky, then we know that there is gas which has been heated to several million degrees, and one of the mechanisms to achieve that is the accretion disc around the black hole. Now about actual discovery: In the early 1970s, an intense X-ray source was found in the constellation Cygnus called Cygnus X-1. As the years passed, in the 1972, Cygnus X-1 was identified with a star known by its classification number HDE226868 (which is a radio source). Soon evidence was found that it is a binary star system with a period of about 5.6 days.

By the special Theory of Relativity, no information can travel faster than the speed of light. Hence, a celestial object cannot change its luminosity on a time scale shorter than the time taken for the light to reach from one side of it to the other. Analysis of Cygnus X-1 showed that its emission had luminosity variations on time scales as short as thousandths of a second, suggesting that the object was only a few kilometers wide. Thus evidence was found that one of the stars was a compact object. Finally, astronomers used the binary star system to determine the mass of the compact object and found that it was greater than the critical mass, so that it was most likely a black hole. That is about the discovery of the first black hole in our universe.

18 December 2007

Look for Mars

This is the perfect time to watch Mars in the sky. Mars will come to its opposition on December 24th, 2007 in the constellation of Gemini. By opposition I mean that Sun, Earth and Mars will lie in a perfect straight line is such a way that Mars will be exactly opposite to the Sun from Earth. Mars will be seen over head at midnight on its opposition.

But six days earlier to it, that is today, December 18th, 2007, Mars will be at its closest to the Earth. Mars will be just 88.42 million km from Earth and from today for a week it will be the perfect time to look out for Mars in the sky. The magnitude of Mars will be -1.5. Magnitude is nothing but the brightness of an object in the sky. The object is brighter when it is negative. Sun, the brightest object in the sky is of magnitude -26.8. The brightest star, Sirius is of magnitude -1.46. So Mars will be bright enough to be noticed.

Look out at the east about an hour or two after sunset. If you don’t know which is east look at the direction opposite to the direction where the sun had set. Between North-East and East you should be able to see a bright star which is Mars. Be careful not to misjudge Sirius, the brightest star, with Mars as Sirius will also be present somewhere nearby. Mars will be a little reddish compared to Sirius.

Check out this site. It is a digital planetarium which shows the complete night sky. I’ll try to help you to find Mars using this.


Set the date and the time on the top left corner of the page. Set the latitude and the longitude of the city you are living at present. For latitude the positive value is north and the negative is south. For longitude positive is east and negative is west.

For example set to latitude to 13 and longitude to 80 (For Chennai, Tamil Nadu, India) and set the time to 18:00:00 and the date to 18th December, 2007. Rotate the sky such that you face east. Near the horizon on the east you should be able to see a tiny red star, which labels as Betelgeuse in the constellation of Orion. Mars should be seen somewhere around the left of the star. But you cannot spot it in this website as it only shows the stars. Try to spot those stars you can spot Mars easily.

In this picture you can see the full moon. The white streak of light is the movement of the space station and a tiny dot below it is the Mars.

Hope you find Mars. You can go to a planetarium nearby to view Mars through the telescope. If you are lucky you may be able to see its two satellites – Phobos and Deimos.

16 December 2007

The Life of a Star

What is a Star? A star is a hot body of glowing gases that emits light and undergoes nuclear reaction. This is the only difference one can point out between a star and a planet. There are billions and billions of stars found in our galaxy, The Milky Way. There are thousands of galaxies in the Universe. It is said that there are more stars in the universe than the number of grains of sand found in all the beaches of the Earth. It is predicted that there are 100 billion stars in the Milky Way. Stars vary in their size, mass, temperature, density, etc. No two stars are alike just as no two humans are alike (left alone the identical twins). But yes, the stars do look alike as you watch them in the night but if you watch them carefully you can see that some stars are bright and some are comparatively less bright.

Stars, just like life, have birth and death of its own. Stars live for a period of time and then it dies. By saying stars I also include the Sun. At average stars live upto 10 billion years. Let’s see how a star is born.

Birth of a Star:

Usually a star is born in a region of high density Nebula. Nebula is nothing but a cloud of dust in the space in which stars and planets are born. Nebulae are visible to our naked eye as a tiny coloured patch of light. The Orion Nebula is one of the brightest nebula situated in the Orion Constellation.

The picture above shows the orion nebula at the bottom left and horse head nebula at the top right. This nebulae is found in the constellation of Orion.

When the nebula condenses and contract under its own gravity it creates a new star. The region of condensing matter will begin to heat up and it starts to glow. These glowing bodies are called as protostars.

The above picture shows a protostar in a nebula. The x-ray version does not show the protostar but you can clearly see them in an Infrared version of the image.

When a protostar contains enough matter the central temperature reaches 15 million degrees centigrade. At this temperature nuclear reactions starts where Hydrogen fuses to form Helium. The star then begins to release energy stopping it from contracting. Now it is called as Main Sequence Star. Sun is in Main Sequence Star level. A star is said to be in its Main Sequence Level for 10 billion years before it starts to die. Sun is said to be 5 billion years old and it is said to live for 5 billion more years.

Death of a Star:

A star is considered dead when all the hydrogen is burnt into helium. But what happens to a star after its death? There are two possibilities based on their mass.

Mass of the Star is under 1.5 times the mass of the Sun:

If the mass of the star is less than 1.5 times the mass of the Sun then as the hydrogen gets less the star begins to expand. The expanding star is called as a Red Giant.

The above picture shows the size comparison of a Red Giant with the Sun and the Earth.

The helium core runs out, and the outer layers drift of away from the core as a gaseous shell, this gas that surrounds the core is called a Planetary Nebula.

The picture above shows the Boomerang planetary nebula where a shell covers around a star.

The remaining core (that’s 80% of the original star) is now in its final stages. The core becomes a White Dwarf the star eventually cools and dims. Sirius, the brighest star in the sky is a White Dwarf. When it stops shining, the now dead star is called a Black Dwarf.

The picture below shows the white dwarfs which are circled.

Mass of the Star is greater than 1.5 times the mass of the Sun:

If the mass of the star is greater than 1.5 times the mass of the Sun then as the hydrogen gets less the star begins to expand just as the previous case. But here the star becomes massive in size and it is called as a Red SuperGiant.

The above picture is a size comparion of a Red SuperGiant Aldebaran with the Sun.

The SuperGiant then starts of with a helium core surrounded by a shell of cooling, expanding gas. In the next million years a series of nuclear reactions occur forming different elements in shells around the iron core. The core collapses in less than a second, causing an explosion called a Supernova, in which a shock wave blows of the outer layers of the star. The actual supernova shines brighter than the entire galaxy for a short time. The bright object at the top left corner (arrowed) is a supernova explosion.

Sometimes the core of the star survives the explosion. If the surviving core is between 1.5 to 3 times the mass of the sun, it contracts to become a tiny, very dense Neutron Star. If the core is much greater than 3 times the mass of the sun, the core contracts to become a Black Hole.

15 December 2007

Picture of the Month - December 2007

If you take a picture of the Sun at the same time each day for a year, would it remain in the same position? The answer is no.

The shape traced out by the Sun over the course of a year is called an Analemma. The Sun's apparent shift is caused by the Earth's motion around the Sun when combined with the tilt of the Earth's rotation axis. Earth does not move around the Sun in a perfect circle. The Earth's orbit is rather elliptical. So at some part of the year Sun is closer to the Earth and at some part it is farthest. Earth's axis is tilted at an angle of 23° which gives out seasons. During summer the Sun will appear at its highest point of the analemma and lowest during winter.

Analemmas created from different Earth latitudes would appear at least slightly different, as well as analemmas created at a different time each day. The analemma pictured on top was built up by Sun photographs taken from 1998 August through 1999 August from Ukraine. The foreground picture from the same location was taken during the early evening in 1999 July.

26 August 2007

Picture of the Month - August 2007

Realize what it is? Well, here is what the Earth looks like during a solar eclipse. This photograph was taken from the Mir Space Station during August 11th, 1999 solar eclipse. The shadow of the Moon (dark part) moves across the Earth at nearly 2000 km per hour. Only observers near the center of the dark circle see a total solar eclipse. Others see a partial eclipse where only part of the Sun appears blocked by the Moon. There are two bright spots on the upper left which are possibly Jupiter and Saturn (which is not proved yet).

12 July 2007

Picture of the Month - July 2007

This is one of the rarest image I have ever seen. Well, I guess you can't see anything other than the blue sky with some clouds in it. Click on the picture for a clear view. You can see a very thin crescent Moon and a crescent Venus next to it. Click here to know more about the 'Phases of Venus'. Both Moon and Venus are bright enough to be seen in the daylight (few minutes before sunset). This image was taken at Budapest, Hungary. Few minutes after this photograph was taken the Moon eclipsed the planet.

25 June 2007

The Unidentified Flying Objects (UFO) - I

Here is another interesting topic that people would love to discuss about – The UFO. UFO is an abbreviation of Unidentified Flying Objects. There is a misconception that UFOs are Alien Space Ships (space ships coming from other planets) but UFOs are simply objects found in the sky which could not be identified. For the past 75 yrs millions of evidences of UFO have been recorded but most of them had no proper explanation of the flying object. Some of the UFOs were later identified as weather balloons or private aircrates. But the most of them could not be explained what so ever and hence the only possibility that people could think of is the alien space ships.

Thousands of UFO evidences comes up every year, from every other country. Some of them with proofs like photographs and videos. Some of the UFO viewers say that they have seen aliens inside the space ship. But the interesting fact I found quite recently was that there was tales of alien abduction??? Tales such as Aliens abducting people and carring out tests. I don't know how much this can be true. But so far there has been no proof of the aliens on Earth. A leading Dutch hypnotherapist, Hilda Musch, had hypnotized various victims who have been abducted (or they say so) and later found that the stories of most of them were alike. The reports of the Dutch victims also seemed to be identical in every respect to such reports taken in the United States. These people could not have possibly met or shared the story of the Alien Abduction as this report was carried out secretly.

In this computer era you cannot expect anyone to believe a photograph or a video proof. A photoshop is all you need to create a photo proof of a UFO. But there is a possibility that some of them can be true. Some of the photos were taken in 1950s when there was no photoshop to create the fakes.

Well, there is nothing more to say about the UFOs other than the debate whether they really exists or not. On my opinion, I personnaly think that Earth cannot be so special that it is the only planet which contains life. There must be living souls in other planets as well (though not all). I also believe that there is a possibility that such living creatures can visit Earth. But I feel that most of the UFO pictures I found were fakes. Very few I have seen that makes me beleive it could be true.

There is a UFO sighting in INDIA recently. On March this year two UFOs were sighted flying over Delhi Airport. This report was telecasted on CNN-IBN news channel. Click Here to see the report with the video of the UFO. Click Here to read the full article.

Let us see some of the pictures of UFO.

These two photos are probably the oldest photos I found. The one on left was taken over Passaic, New Jersey on 31st July, 1952. It is taken from an FBI document. The one on the right was taken at Brazil.

This is an interesting one. I'm not sure of its location. Its one of the few photos showing a UFO that looks like a space ship. But I also feel that this one is a fake. It looks like a family is out for a picnic and they must be playing around. And the UFO must be added using a photoshop that makes it look like people are running away from it.

Here is another one. This was taken from Google Earth. This object within the circle was found over california, USA. I could not guess what this object is. Google Earth replaced this area with another one and hence this cannot be found any more.

This certainly looks like a fake. This object, what ever it is should have been on top of a building or a pillar. All the parts below the object must have been removed through Photoshop.

This picture is certainly a fake. Just closely look at the UFO. It looks like an object used in the mechanical workshop. It looks like the object was photographed in a close up and the two images are collaged. Moreover the shadow of the car is clearly seen. Where is the shadow of the UFO???

I have no comments on this photo.

This photo was taken at Knoxville, Tennessee, USA.

Here is how the fakes are created.

First the model of the UFO is created (Left).

Then it is photographed in various angles (Right).

Then these photos are collaged with some of the scenaries using the photoshop. And the result is as in below.

The collaged pictures looks too realistic. I wonder if all the pictures are taken as this.

Here is a website that has a big collection of UFO photographs. http://www.ufoevidence.org/photographs/view/newer.htm

The Unidentified Flying Objects (UFO) - II

Let us look at some of the videos of UFO.

Here are the secrets of UFO. A Must watch video.

This video is taken in an helicopter near the World Trade Center. An
object is found on the window of the WTC. The most surpricing thing is
that no object on Earth has ever flew at that high speed (including

This is the same as the above. This is the slower version taken from a
Japanese News Channel. There is a surprise here.

A very rare event. UFO seen not in the sky but in space. Viewed from
the camera of the space shuttle 'Discovery'.

Here is a collection of UFO sightings. A very interesting one.

Any guesses on what that object is???

Another interesting video where a UFO lands on Earth.
Click here to view it.

This topic was requested by Kavin.

13 June 2007

Picture of the Month - June 2007

Here's another interesting picture I found on the net. This picture is a fusion of two images. One is the visit of Apollo17 to our satellite and the other is a picture of the Earth. It is fused in such a manner that it looks like Earth is eclipsing the Sun or it is the Solar Eclipse observed in Moon. This picture tries to explain that eclipses not only occur in Earth but in any planets or satellites in our solar system. When Earth comes in between Sun and the Moon, solar eclipse can be observed on Moon whereas it would be a Lunar Eclipse on Earth.

Unlike the solar eclipse on Earth, when you observe the same event on Moon you would find that Earth completely blocks the sun. The Night Earth would be visible in this case as the reddened Moon (total lunar eclipse) reflects the light.

This picture simply tells us that this is how a Solar Eclipse would be viewed from Moon.

14 May 2007


Hi Friends! I hope this blog has been interesting so far. I have decided to make it more interesting. I have been giving some interesting facts to you but now you can ask me any topic you are interested and I'll try to post related to it. You can also ask me any queries and I'll try to answer them as soon as possible. You can ask me your queries via e-mail or the chatter box in this blog. You can mail me to incharaprakash@gmail.com Hope you would find this interesting.

6 May 2007

The Secrets of Mars

Mars – named after the Roman God of War – is the fourth planet in our solar system. It has two natural satellites revolving around it - Phobos and Deimos.

This picture shows Mars along with its two satellites Phobos and Deimos with Sun behind the Mars

Both these satellites are named after the sons of Ares (Mars) from Greek Mythology. These satellites are quite unique in their nature. They are actually escaped asteroids which are bound under the gravity of Mars. The picture on the left is Phobos and the one below is Deimos.

Asteroids are tiny pieces of rocks which are found in between the orbit of Mars and Jupiter which orbits the Sun. The picture below shows the Asteroid belt. Phobos and Deimos escaped from their orbit and they were captured by the strong gravitational force of Mars. Thus Phobos and Deimos were forced to orbit around the Mars.

Phobos has a unique property. It moves very close of the planet; it moves approximately at a distance of 9380 km away from Mars. Phobos also orbits at a very high velocity such that the time taken for Phobos to make one revolution around Mars is quicker than the time taken for Mars to make one rotation around its axis. Due to this Phobos appears to rise in the west and set in the east unlike any other satellites in our solar system. Also due to the high velocity Phobos rises and sets twice in one Mars day (which is also aprrox. 24 hrs.) This makes Phobos a unique satellite in our solar system.

The above picture shows the orbital motion of the two satellites of Mars.

1 May 2007

Picture of the Month - May 2007

(Click on the picture for the best view)

This series of images which was taken by a satellite and fused together shows the Earth during the night time. The continents are seen clearly due to the light of the Full Moon. But what is more astonishing is the brightness of the city lights. The city lights are so bright that it could actually be seen from space. These lights mark the developed areas on Earth. The eastern part of USA and west Europe are the brightest parts which are considered as the most developed areas. Whereas in Asia, Japan, east coast of China, Malaysia, Singapore and most parts of India are glittering with the city lights.

6 April 2007

The Green Sun

Confused by the title? I'm not trying to make an April Fool here. We have indeed witnessed the Green Sun. This video of the setting Sun from a site atop Mt. Autore (altitude 1,850 meters) in Italy has captured a green flash while the Sun was setting. How can the Sun turn green? Why does it occur? When can we observe this phenomenon?

(The time between frames in the gif image above varies from over one minute in the beginning to about one second as the flash becomes visible. If the image is not changing try to refresh the page.)

It is quite difficult to observe the Green Flash. It usually occurs during sunrise or sunset. This phenomenon is caused by the atmospheric bending or refraction of sunlight. Like a weak prism, the Earth's atmosphere breaks white sunlight into the seven colours, bending red colours slightly and green and blue colours through increasingly larger angles. When the sky is clear, a green flash just above the Sun's edge can sometimes be seen for a second or so, when the Sun is close to the horizon.

The above image was taken at the western horizon of Madagascar

This image of Green Flash was taken at the La Silla Observatory, in Chile, on October 15, 2005. The sun has almost set behind the mountain ranges of the western Chile when the Green Flash was observed.

Note: Click on the pictures for a better view.

Picture of the Month - April 2007

Brilliant Venus, slender crescent Moon, and lights along the Ponte 25 de Abril, which is a 2.3 km long suspension bridge across Tagus river glow against the western twilight in this lovely Moonset scene from Lisbon, the capital city of Portugal, recorded on March 20, 2007. In fact, such serene views were enjoyed across planet Earth this week, as the young Moon remained near the setting Sun following a partial solar eclipse, and Venus ruled as the evening star. Because of strong Earthshine - light from the sunlit Earth - even the Moon's night side is clearly visible in the picture.

5 February 2007

Picture of the Month - February 2007

This is dedicated to my friend who was asking me to change the usual topic - Astronomy. This brilliant photo was taken just a second before the Sand Storm that took place at Sumatra Island, Indonesia. This photo was found in a digital camera which was found about one month after the disaster.

28 January 2007

Goddess of Love - Venus

Hi everyone. This is the right time for us to see a Goddess with our own eyes – it’s the Goddess of Love. Goddess of Love is nothing but the planet ‘Venus’. Venus is the Greek Goddess of Love and Beauty. The Planet is named so because it is the brightest object in the sky let alone Sun and Moon. The picture below shows the planet Venus taken by a spacecraft.

Venus is the brightest object because its atmosphere consists of carbon dioxide and thick clouds of Sulphuric Acids which covers the planet completely. We can never see the surface of Venus unless we go into its atmosphere. Due to this reason Venus acts as a ‘Green House’. Thus the atmosphere of Venus reflects more than 95% of the light from the sun making it the brightest object in the sky. During the early periods Venus was confused for a UFO. The bright star on the top left of the picture below is the Planet Venus. We can clearly see that Venus is very bright compared to the other stars.

Venus is one of the two Inferior Planet (the other being Mercury). Inferior planets are simply planets whose orbits are within the orbit of Earth. Since Venus is the Inferior Planet we can only see the planet near the Sun i.e. either before sunrise or after sunset. When Venus is seen in the morning before sunrise it is called as the ‘Morning Star’ and when it is seen in the evening after sunset it is called as the ‘Evening Star’.

We can see Venus through our naked eye. It looks like any other star but no star can match its brightness. When you look at the planet through a telescope you can see special phenomenon which can only be noticed by the inferior planets. But Mercury is too close to the Sun and so only Venus exhibit this character very clearly. So far this phenomenon has only been noticed in the Moon, yet it is more special in Venus. This phenomenon is nothing but the ‘Phases of Venus’. It is no different from that of the Moon. Just as Moon, Venus changes its phases from ‘New Venus’ to ‘Full Venus’ and again back to ‘New Venus’. But this effect can only be viewed through a telescope.

When Venus is behind the Sun we can see the full phase of Venus. As Venus moves through its orbit it reduces its shape into a Gibbous, just like Moon. When Venus is exactly at right angles to Sun and Earth we can see Half-Venus. And as Venus continues to move around the sun and as it comes in-between the Earth and the Sun, it reduces its shape to a cresent and finally a new-Venus, exactly as that of the Moon. Yet, there is something different in its formation of phases which makes it phenomenon. During the full phase, the Venus is usually behind the sun and hence it is smaller in size due to the longer distance from the Earth. But during the cresent, Venus comes in-between Sun and Earth and hence it appears larger in size. So as Venus goes around the Sun it not only changes its shape but also its size. This phenomenon could also be seen in Mercury but to a small extent.

The picture below shows the different phases and the sizes of Venus during April-May 2004.

When Venus is exactly in between in the orbit of Earth and Sun we can see its Transit. Transit of Venus is nothing but the movement of Venus on the surface of Sun. We can see Venus as a dark spot on the sun. The picture below shows the transit of Venus over the surface of Sun. The dark spot on the Sun in the left is Venus.

The first person to notice the Phases of Venus is Galileo Galilei with his newly invented telescope. We can now see Venus at this very day as the ‘Evening Star’. We can see the planet clearly with our naked eyes. It looks just like a star but look for the brighest in the west. It is so bright that you can see the planet even before it gets dark completely. The planet will be visible until an hour or so after sunset.

If you want to look at the phases of Venus go to a planetarium nearby.

3 January 2007

Picture of the Month - January 2007

Hi Friends! From this year on, I'll post some exciting pictures every month for you all.

This picture shows the full moon with Andromeda Galaxy(aka M13) in the background. This galaxy is only about 2.5 million LY (Light Years) away and it is known as the closest spiral galaxy to Milky Way. This entertaining image compares the zoomed in image of the galaxy and the normal sized image of the mooon with the same angular view. In the normal view this galaxy looks like a small, faint, fuzzy patch near the constellation of Andromeda.