Parsec (pc)

1 pc = 3.08 x 10¹⁶ m

One parsec (pc) is the distance to a star that subtends and angle of 1 arc second at an arc length of 1 AU.

Parallax is “the best way to get distance in astronomy,” said Mark Reid, an astronomer at the Harvard Smithsonian Center for Astrophysics. He described parallax as the “gold standard” for measuring stellar distances because it does not involve physics; rather, it relies solely on geometry.

The Vernier calliper is used to measure the length or thickness of an object with great accuracy. It was invented by Pierre Vernier in 1630. It can measure length less than 1 mm.
A Vernier calliper consists of a fixed main scale or ordinary scale, a sliding Vernier scale, movable jaws, and a tail.
Parts of a Vernier Calipers

Main Scale: The main scale consists of a steel metallic strip graduated in centimeters at one edge and in inches at the other edge . It consists of a fixed external jaw and a fixed internal jaw.
Vernier Scale: A vernier scale  slides on the strip. It can be fixed in any position by the retainer. On the Vernier scale, 0.9 cm is divided into ten equal parts. It consisits of a fixed external jaw and a fixed internal jaw.

External Measuring Jaws: The outer measuring jaws (one of the main scale and the other of the vernier scale) helps to take the outer dimension of an object

Internal Measuring Jaws: The inner measuring jaws (one of the main scale and the other of the vernier scale) helps to take the inner dimension of an object.
Retainer: The retainer helps to retain the object within the jaws of the Vernier calipers to fix firmly.
Depth Measuring Strip: The depth measuring strip (prong) helps to measure the depth of an object. 

Least Count: The smallest length that can be measured accurately with a device is called the least count of that device. The least count of a Vernier calliper is known as the Vernier constant.

The least count or the smallest reading which you can get with the instrument can be calculated as:

Least Count = One main scale division - one Vernier scale division ------------ (i)

The greenhouse effect is the trapping of the sun's heat in the atmosphere of a planet by gases in that atmosphere. The green house effect happens because of so-called greenhouse gases, which includes carbon dioxide, methane, water vapor & other. The greenhouse effect is hugely significant.

• Viscosity is the property of a fluid that resists the force tending to cause the fluid to flow.
• It is analogous to friction in solids.

The 1878 Forest Act, divided forests in India into three categories reserved, protected and village forests.
The consequences of this Act were :

1. Villagers used forests for different needs, i.e. for fuel, fodder and leaves. After Forest Act they could not take anything from the reserved forests.
2. In forest areas people graze their cattle, collect fruits and roots and hunt animals and fish. Almost everything was available in the forest for their livelihood. The Forest Act meant severe hardship for them. All their practices became illegal.
3. Circumstances forced the villagers to steal wood and if they were caught, forest guard claimed bribe from them. Women who collected fuelfood were scared of the forest guards as they harassed them and demanded free food.
4. After the Forest Act, the forest department only encouraged to plant Teak and Sal tree for commercial uses.