Distances can be measured within 10% as far as the Galactic Center, about 30,000 light years away. The Gaia space mission provided similarly accurate distances to most stars brighter than 15th magnitude. The Hubble Space Telescope's Wide Field Camera 3 has the potential to provide a precision of 20 to 40 microarcseconds, enabling reliable distance measurements up to 5,000 parsecs (16,000 ly) for small numbers of stars. In the 1990s, for example, the Hipparcos mission obtained parallaxes for over a hundred thousand stars with a precision of about a milliarcsecond, providing useful distances for stars out to a few hundred parsecs. Astronomers usually express distances in units of parsecs (parallax arcseconds) light-years are used in popular media.īecause parallax becomes smaller for a greater stellar distance, useful distances can be measured only for stars which are near enough to have a parallax larger than a few times the precision of the measurement. The amount of shift is quite small, even for the nearest stars, measuring 1 arcsecond for an object at 1 parsec's distance (3.26 light-years), and thereafter decreasing in angular amount as the distance increases. These shifts are angles in an isosceles triangle, with 2 AU (the distance between the extreme positions of Earth's orbit around the Sun) making the base leg of the triangle and the distance to the star being the long equal-length legs. As the Earth orbits the Sun, the position of nearby stars will appear to shift slightly against the more distant background. The most important fundamental distance measurements in astronomy come from trigonometric parallax, as applied in the stellar parallax method. A similar diagram can be drawn for a star except that the angle of parallax would be minuscule. The lower diagram shows an equal angle swept by the Sun in a geostatic model. In the upper diagram, the Earth in its orbit sweeps the parallax angle subtended on the Sun. Parallax is an angle subtended by a line on a point. Half the apex angle is the parallax angle.

To keep itself informed of and study critically the status of physics.Stellar parallax motion from annual parallax.

To assist industries, national and other agencies in their developmental tasks by precision measurements, calibration, development of devices, processes, and other allied problems related to physics.

To identify and conduct after due consideration, research in areas of physics which are most appropriate to the needs of the nation and for the advancement of the field.

To establish, maintain and improve continuously by research, for the benefit of the nation,.

To strengthen and advance physics-based research and development for the overall development of science and technology in the country.

The weights and balances used in local markets and other areas are expected to be certified by the Department of Weights and Measures of the local government.

It is the responsibility of the NPL to calibrate the measurement standards in these laboratories at different levels.

Responsibility of National Physical Laboratory (NPL): Physical quantities can only be added if they have the same Units Currently Accepted for Use with the SI System: NameĬalculation of number of kilometers in 20 miles:Ĭonversion factors a mile = 5280 ft, 1 ft = 12 in, 1 in = 2.54 cm, 1 m = 100 cm, 1 km = 1000 m.Ģ0 miles = 20 × 5280 ft = 20 × 5280 × 12 inches Units outside SI but Frequently Used in Physics: Name

shake is used to measure very small time.

Extremely small areas are measured in barn.Mass is measured in slug, metric ton, quintal.

1 chandrashekhar unit = 1.4 times mass of the Sun. Chandra Shekhar unit is practical unit of measuring large masses.One a.m.u.: It is defined as 1/12 th of the mass of one atom. 1 a.m.u.A light-year (ly), parsec (pc) are used to measure the distance between stars and the astronomical unit is used to measure the distance between planets. Note that light-year (ly) and parsec (pc) are units of distances and not of time.

Parsec distance