Days in the Sun

From solstice to solstice, this six month long exposure compresses time from the 21st of June till the 21st of December, 2011, into a single point of view.

Wolf Moon

A full moon looking yellowish-orange, which the ancients and old people dubbed as wolf moon, accompanied by many mythical stories.

A Star Factory

These are the places in the Milky Way galaxy where stars are formed. Awesome, isn't it?

The Ghost Nebula

The Ghost Nebula, after being captured by the Hubble space telescope

Saturn's Iapetus Moon

This is Saturn's Iapetus moon, which looks painted and colorful, setting it apart from the other moons.

Saturday, February 26, 2011

Stars

   Star is a huge, hot, shining ball of burning gases in space that produces a tremendous amount of light and other forms of energy. The Sun is a star, and it supplies Earth with light and heat energy. The stars look like twinkling points of light except for the sun. So are they really a point? No. The stars that we see in the night sky look like a point because they are very far away from us, millions of light years away. In fact the nearest star to us is the sun itself, which is about 149 million km or 93 million miles away from us.
A region where a star is forming


   Stars come in many sizes. The sun's radius is about 432,000 miles across. But astronomers classify sun as a medium sized star because other stars are much bigger than the sun. Some stars are known as red supergiants which are about a 1000 times bigger than the sun. The smallest stars are neutron stars. They are about 6 - 7 miles across in radius. But they are a 1000 times hotter than the sun. The surface temperature of the neutron stars may be twice as hot as the sun's core.
Neutron Star
   Why do stars twinkle? Stars are way far from our planet, Earth. The light that comes from them is a very little amount. And about 70% of the light is reflected back into space by the atmosphere. The 30% of it refracts through air (refractive index of vacuum - 1.000; refractive index of air - 1.003) So with this refraction and also because of the disturbance in the ever moving wind, the ray of light bends and breaks making it to look like its twinkling.

Nuclear Fusion
  Stars are basically made up of Hydrogen(H) and Helium(He) much like our own sun.These elements are very close to each other. Thus the atoms of hydrogen and helium keep colliding with each other forming new elements and atoms. This process is called Nuclear Fusion reaction. This releases a huge amount of energy as heat and light. 2 atoms of Hydrogen fuse together to form a Helium atom. The fusion of just two atoms liberates around 1kilo Joules(kJ). That is why the sun appears to be red.




Classification of stars: For the convenience of study of stars, they were classified into groups. This classification is called stellar classification.
1) Spectral class: This type of classification deals with the state and description of ionization of its chromosphere with atomic excitations. The light coming in as photons are diverted into prisms to to obtain a spectrum. The spectral lines are thus formed showing certain type of ion.These ions show a particular chemical element. By interpreting these, scientists can tell what type of star it is.
2)Temperature: In the beginning stars were classified according to their temperature. Their temperature showed the colour of the stars They were as follows.

Red                    -               cool(4000 - 6000 K)
Orange               -               warm(6000 - 8000 K)
Yellow               -                hot(8000 - 12000 K)
White                 -               very hot(12000 - 16000 K)
Blue-White         -               too hot(16000 - 20000 K)
Blue                   -                Super hot( >20000 K)
This classification was discarded because of some reasons but still used sometimes.



Now Stars are classified as O, B, A, F, G, K and M. Conventionally, to remember this, it is made into a sentence - Oh!!, Be A Fine Guy/Girl, Kiss Me.
Like the previous way, these are also according to temperature.

O - Blue:


B - Blue - White:



A - White:
Class A compared with the Sun
Class F(Polaris)
                         F - Yellow - White:












G - Yellow: 
Class G
                                          

                                   K - Orange:
Class K








M - Red:

Class M














ClassTemperature[8]
(kelvins)
Conventional colorApparent color[9][10][11]Mass[8]
(solar masses)
Radius[8]
(solar radii)
Luminosity[8]
(bolometric)
Hydrogen
lines
Fraction of all
main sequence stars[12]
O≥ 33,000 Kblueblue≥ 16 M≥ 6.6 R≥ 30,000 LWeak~0.00003%
B10,000–33,000 Kblue to blue whiteblue white2.1–16 M1.8–6.6 R25–30,000LMedium0.13%
A7,500–10,000 Kwhitewhite to blue white1.4–2.1 M1.4–1.8 R5–25 LStrong0.6%
F6,000–7,500 Kyellowish whitewhite1.04–1.4 M1.15–1.4R1.5–5 LMedium3%
G5,200–6,000 Kyellowyellowish white0.8–1.04 M0.96–1.15R0.6–1.5 LWeak7.6%
K3,700–5,200 Korangeyellow orange0.45–0.8 M0.7–0.96R0.08–0.6 LVery weak12.1%
M≤ 3,700 Kredorange red≤ 0.45 M≤ 0.7 R≤ 0.08 LVery weak76.45%
                                                                 (source for the table - Wikipedia)

The sun that we see is a Orange star, which means its a cool star. 


Yet another star classification has been made according to their sizes. This type of classification is called as 
Yerkes Stellar classification.


1)Black dwarf: 

                          






                      



                                                                                                                        2)White dwarfs:
                                                                                     
                                                                                                          
                                                                                                                                                A White Dwarf

3) Sub-dwarfs:
A Sub-Dwarf star in the
 center of a nebula











                                                                         4)Dwarfs: 
                                                                                   
                                                                                         




                              










                5)Sub-Giants:














                                                                              6)Giants: 




                                                                                       

      






7)Bright-Giants:


                                       


                                                                  8)Supergiants : 
                                                                             


                                                                                                                     




                                                                      9)Hypergiants:



                                                              
                                                                  Hypergiant


                                                         
                                     




Saturday, February 19, 2011

Galaxies

    Galaxy is a system of stars, dust and gas held together by gravity. Galaxies are the building blocks of our solar system. Our solar system is in a galaxy called the Milky Way galaxy. Scientists estimate that there are more 100 billion galaxies scattered throughout the visible universe then just think how many more might be there. Astronomers have photographed millions of them through telescopes. The most distant galaxies are as far as 10 billion to 13 billion light years away. Galaxies range in diameter over a few thousand to a half-million light years. Small galaxies have fewer than a billion stars. Large galaxies have more than a trillion.

    Galaxies are distributed unevenly in space. Some have no close neighbour. Others occur in pairs, with each orbiting the other. But most of them are found in groups called clusters. A cluster may contain from a few dozen galaxies to several thousand galaxies.

   Classification of galaxies:
Galaxies are classified under their shape
1)Spiral galaxies: Galaxies that are shaped like spirals contain new and old stars. Spiral galaxies are identified by their curved arms, which form a spiral around their center. Some of the biggest and the best known galaxies are spirals, like our own Milky Way Galaxy and the great Andromeda Galaxy.
Spiral Galaxy
2)Elliptical galaxies: Elliptical Galaxies are made up of ancient stars. Some elliptical Galaxies are flat like pancakes, while others are round
Elliptical Galaxy
3)Irregular Galaxy:  Some galaxies have no particular shape. They may look like a twisted saucer or an odd shaped ball. These are irregular galaxies.
Irregular Galaxy
4)Lenticular galaxies: A galaxy which is an intermediate between an elliptical galaxy and a spiral galaxy are know as Lenticular galaxies. They are disk galaxies, like spiral galaxies but contain very small amount of interstellar dust, thus having very little amount of star formation.
Lenticular Galaxy


5)Barred spiral galaxies:
Barred Spiral Galaxy
The Milky Way Galaxy: Milky Way galaxy is the galaxy in which we live. The solar system is situated in this galaxy. The solar system in fact rotates around the milky way galaxy once in every 1,250,000 years. Huge clouds of gas and dust lie through out the galaxy and form new stars everyday. The milky way is so humongous that 10 other small galaxies orbit around it like the planets revolve around the sun.
The core of the Milky way galaxy
Infrared Image

   The milky way is shaped like a thin disk with a bulge in the center. The bulge consists of a vast, thick bar of stars. Stars, dust, gas fan out from the central bulge in long, curving arms that form a spiral(coiled) pattern. Astronomers believe that the spiral patterns originate from the ends of the bar. Therefore, they classify Milky Way as a barred spiral galaxy. Barred spirals are a common type of galaxy, though not as common as spiral galaxies without bars.

Andromeda Galaxy
The Andromeda Galaxy: The Andromeda Galaxy is a spiral galaxy approximately 2.6 million years away. The Andromeda can be seen from the North Pole. The Andromeda galaxy was thought to be bigger than the milky way but it has been proved wrong in the year 2006. It is as huge as the Milky way Galaxy is. The Andromeda gets its name from the Andromeda constellation.

 A picture of Andromeda by
NASA
  The Milky Way galaxy and the Andromeda are heading towards each other slowly. They are expected to collide in about 4.5 billion years creating a massive explosion in the universe.







Small Magellanic Cloud
Large Magellanic Cloud
 From the Southern hemisphere two more Galaxies can be seen with the naked eye. They are called as the Large Magellanic Cloud and the Small Magellanic Cloud. Both are Irregular Galaxies. They are 160,000 and 180,000(approximately) light years away from the milky way.




Cannibal Galaxies: These types of Galaxies are not special divisions, but these are special types of humongous galaxies. These Galaxies are also called the Hungry galaxies. They are so big that they swallow up their neighbouring small galaxies.Even the Milky way is believed to be a Cannibal Galaxy which will in time swallow Sagittarius, a small neighbouring galaxy.

Sagittarius Galaxy


   

Friday, February 18, 2011

How do our speakers work?

Moving coil microphone or dynamic microphone: 


The construction of a dynamic microphone resembles that of a loudspeaker, but in reverse. It is a moving coil type microphone which has a very small coil of thin wire suspended within the magnetic field of a permanent magnet. As the sound wave hits the flexible diaphragm, the diaphragm moves back and forth in response to the sound pressure acting upon it, and the attached coil of wire also moves within the magnetic field of the magnet. The resultant output voltage signal from the coil is proportional to the pressure of the sound wave acting upon the diaphragm so the louder or stronger the sound wave the larger the output signal will be, making this type of microphone design pressure sensitive.
As the coil of wire is usually very small the range of movement of the coil and attached diaphragm is also very small producing a very linear output signal which is 90o out of phase to the sound signal. Also, because the coil is a low impedance inductor, the output voltage signal is also very low so some form of "pre-amplification" of the signal is required.
As the construction of this type of microphone resembles that of a loudspeaker, it is also possible to use an actual loudspeaker as a microphone. Obviously, the average quality of a loudspeaker will not be as good as that for a studio type recording microphone but the frequency response of a reasonable speaker is actually better than that of a cheap "freebie" microphone. Also the coils impedance of a typical loudspeaker is different at between 8 to 16Ω. Common applications where speakers are generally used as microphones are in intercoms and walki-talkie's.

Moving coil loudspeaker or dynamic loudspeaker:
When an analogue signal passes through the voice coil of the speaker, an electro-magnetic field is produced and whose strength is determined by the current flowing through the "voice" coil, which inturn is determined by the volume control setting of the driving amplifier. The electro-magnetic force produced by this field opposes the main permanent magnetic field around it and tries to push the coil in one direction or the other depending upon the interaction between the north and south poles. As the voice coil is permanently attached to the cone/diaphragm this also moves in tandem and its movement causes a disturbance in the air around it thus producing a sound or note. If the input signal is a continuous sine wave then the cone will move in and out acting like a piston pushing and pulling the air as it moves and a continuous single tone will be heard representing the frequency of the signal. The strength and therefore its velocity, by which the cone moves and pushes the surrounding air produces the loudness of the sound.