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.

Sunday, May 20, 2012

Large Magellanic Cloud


The Large Magellanic Cloud (LMC) is a nearby irregular galaxy, and is a satellite of the Milky Way. At a distance of slightly less than 50 kiloparsecs (≈160,000 light-years), the LMC is the third closest galaxy to the Milky Way, with the Sagittarius Dwarf Spheroidal (~ 16 kiloparsecs) and Canis Major Dwarf Galaxy (~ 12.9 kiloparsecs) lying closer to the center of the Milky Way. It has a mass equivalent to approximately 10 billion times the mass of our Sun (1010 solar masses), making it roughly 1/100 as massive as the Milky Way, and a diameter of about 14,000 light-years (~ 4.3 kpc). The LMC is the fourth largest galaxy in the Local Group, the first, second and third largest being Andromeda Galaxy , our own Milky Way Galaxy, and  the Triangulum Galaxy.
While the LMC is often considered an irregular type galaxy (the NASA Extragalactic Database lists the Hubble sequence type as Irr/SB(s)m), the LMC contains a very prominent bar in its center, suggesting that it may have previously been a barred spiral galaxy. The LMC's irregular appearance is possibly the result of tidal interactions with both the Milky Way, and the Small Magellanic Cloud (SMC).
It is visible as a faint "cloud" in the night sky of the southern hemisphere straddling the border between the constellations of Dorado and Mensa.
The very first recorded mention of the Large Magellanic Cloud was by the Persian astronomer, `Abd al-Rahman al-Sufi (later known in Europe as "Azophi"), in his Book of Fixed Stars around 964 AD.
The next recorded observation was in 1503–4 by Amerigo Vespucci in a letter about his third voyage. In this letter he mentions "three Canopes, two bright and one obscure"; "bright" refers to the two Magellanic Clouds, and "obscure" refers to the Coalsack.
Ferdinand Magellan sighted the LMC on his voyage in 1519, and his writings brought the LMC into common Western knowledge. The galaxy now bears his name

Other images of LMC:


Infrared Image

Sunday, May 6, 2012

Critical Angle

Critical angle is the angle at which the light ray travelling form a denser medium to a rarer medium grazes along the surface rather than escaping directly. The angle of refraction in 90° for the angle of incidence equal to critical angle. A ray of light which is incident of the boundary separating the two optical mediums is incident at angle greater than critical angle will get reflected. This phenomenon is called Total Internal Reflection.


The angle of incidence is measured with respect to the normal at the refractive boundary (see diagram illustrating Snell's law). Consider a light ray passing from glass into air. The light emanating from the interface is bent towards the glass. When the incident angle is increased sufficiently, the transmitted angle (in air) reaches 90 degrees. It is at this point no light is transmitted into air. The critical angle \theta_c is given by Snell's law,

n_1\sin\theta_i = n_2\sin\theta_t \quad.
Rearranging Snell's Law, we get incidence
\sin \theta_i = \frac{n_2}{n_1} \sin \theta_t.
To find the critical angle, we find the value for \theta_i when \theta_t = 90° and thus \sin \theta_t = 1. The resulting value of \theta_i is equal to the critical angle \theta_c.
Now, we can solve for \theta_i, and we get the equation for the critical angle:
\theta_c = \theta_i = \arcsin \left( \frac{n_2}{n_1} \right),
If the incident ray is precisely at the critical angle, the refracted ray is tangent to the boundary at the point of incidence. If for example, visible light were traveling through acrylic glass (with an index of refraction of 1.50) into air (with an index of refraction of 1.00), the calculation would give the critical angle for light from acrylic into air, which is
\theta _{c}=\arcsin \left( \frac{1.00}{1.50} \right)=41.8{}^\circ .
Light incident on the border with an angle less than 41.8° would be partially transmitted, while light incident on the border at larger angles with respect to normal would be totally internally reflected.
If the fraction {n_2}/{n_1} is greater than 1, then arcsine is not defined—meaning that total internal reflection does not occur even at very shallow or grazing incident angles.
So the critical angle is only defined when {n_2}/{n_1} is less than 1.

How does our phone Vibrate?


There is a device that takes vibration to high-tech extremes. Any parent whose child owns a Tickle-Me-Elmo doll has experienced this technology. Elmo has a vibration system (designed to simulate body-shaking laughter) that is powerful enough to cause many children to drop the toy. The vibration system inside a pager works exactly the same way on a smaller scale, so let's use Elmo as an example.
Inside the control unit (on the right hand side in the above image) is a small DC motor which drives this gear:You can see that, attached to the gear, there is a small weight. This weight is about the size of a stack of 5 U.S. nickels, and it is mounted off-center on the gear. When the motor spins the gear/weight combination (at 100 to 150 RPM), the off-center mounting causes a strong vibration. Inside a cell phone or pager there is the same sort of mechanism in a much smaller version
.