Chapter 1 · Topic 1.2 · Prelims + Mains2 of 3
Basics of Science: Measurement and instruments
Key points
- 1 au = 149 597 870 700 m. Nautical mile = 1,852 m.
- Light-year (about 9 trillion km) is a distance. Light speed fixed at 299 792 458 m/s.
- CSIR-NPL keeps IST: five caesium clocks, two hydrogen masers, within ±2.9 ns of UTC.
- IST Rules 2026: IST = UTC(NPLI) + 5:30, in force 180 days after notification.
- LIGO-India: Rs 2,600 crore, DAE lead agency.
- IceCube: 86 strings, 1 cubic km of ice, neutrinos and dark matter.
Prelims box: facts and traps
| Instrument | Measures |
|---|---|
| Hygrometer | humidity |
| Anemometer | wind speed |
| Seismograph | earthquake waves |
| Interferometer | tiny length changes |
- Trap: a light-year measures distance, not time.
- Trap (Prelims 2015): all three IceCube statements are correct.
Measurement, big distances and Indian Standard
Time and distance need agreed units. Some non-SI units are accepted for use with the SI (SI Brochure, Table 8):
- the astronomical unit: 1 au = 149 597 870 700 m, roughly the Earth-Sun distance,
- the nautical mile: 1,852 m.
A light-year is the distance light travels in one Earth year, about 9 trillion km (NASA). It is a distance, not a time, like saying a town is “two hours away”. Astronomical distances are measured in light-years because the speed of light in vacuum is always the same, fixed at 299 792 458 m/s (Prelims 2021: answer (d)).
Which one of the following is a reason why astronomical distances are measured in light-years?
- Distances among stellar bodies do not change.
- Gravity of stellar bodies does not change.
- Light always travels in straight line.
- Speed of light is always same.
Show answer
Answer: (d) · UPSC official key
CSIR-National Physical Laboratory (CSIR-NPL), New Delhi, is India’s national measurement institute. It keeps Indian Standard Time using five caesium clocks and two hydrogen masers (very stable atomic clocks). It stays within ±2.9 nanoseconds of Coordinated Universal Time (UTC), the world reference. It gives IST to ISRO’s NavIC timing centres (CSIR-NPL note, PIB).
The Legal Metrology (Indian Standard Time) Rules, 2026 (G.S.R. 761(E), 27 August 2026) define IST as the official time for all civil, commercial and legal purposes. CSIR-NPL realises it by adding 5 hours 30 minutes to UTC(NPLI). They come into force 180 days after Gazette publication (Gazette of India).
Scientific instruments, small and giant
UPSC tests these pairs:
| Instrument | Measures or detects |
|---|---|
| Barometer | air pressure |
| Hygrometer | humidity of the air |
| Anemometer | wind speed |
| Seismograph | earthquake waves |
| Spectrometer | the wavelengths (colours) of light given off or absorbed |
| Interferometer | tiny length changes, by combining light beams |
| Particle detector | particles from collisions or from space |
General reference.
Modern discovery often needs giant instruments. LIGO in the USA uses laser interferometers with arms several kilometres long to sense gravitational waves, ripples in space from events like black holes merging. India’s LIGO-India project has been approved at an estimated cost of Rs 2,600 crore, with the Department of Atomic Energy as lead agency (PIB, 10 August 2023: approved cost, not spending).
IceCube, at the South Pole, is buried under the ice. Its sensors hang on 86 strings frozen into boreholes, spread over a cubic kilometre between 1,450 and 2,450 metres deep (IceCube, University of Wisconsin-Madison). Neutrinos are ghost-like particles that pass through almost everything. It is the largest neutrino detector and is also used to search for dark matter (Prelims 2015: 1, 2 and 3).
In the context of modern scientific research, consider the following statements about ‘IceCube’, a particle detector located at South Pole, which was recently in the news : 1. It is the world’s largest neutrino detector, encompassing a cubic kilometre of ice. 2. It is a powerful telescope to search for dark matter. 3. It is buried deep in the ice. Which of the statements given above is/are correct?
- 1 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer
Answer: (d) · UPSC official key
What UPSC asks: Prelims: au, instruments. Mains: light-year, LIGO-India.
Mains box: analysis and answer points
- Big science: LIGO-India and its gains.
- Time: why a legal IST standard matters for NavIC and finance.
Practice
Write an answer
In 150 words, explain the significance of Basics of Science with one recent example.
Flashcards (8)
1 astronomical unit?
149 597 870 700 m.
1 nautical mile?
1,852 m.
Why measure star distances in light-years?
Speed of light is always the same.
Who keeps Indian Standard Time?
CSIR-NPL, New Delhi.
IST in terms of UTC(NPLI)?
UTC(NPLI) + 5 h 30 min.
Anemometer measures?
Wind speed.
LIGO-India approved cost and lead agency?
Rs 2,600 crore; Department of Atomic Energy.
IceCube volume and depth?
About 1 km³, 1,450-2,450 m deep.
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