Science Original explainer
Your phone listens to clocks in space to find you within metres. How GPS works — and India's own NavIC.
Open a map on your phone and a blue dot appears, showing exactly where you are — often within a few metres. It feels like magic, and it is easy to forget that the dot is the result of a conversation between your phone and clocks in space. GPS, the Global Positioning System, is a network of satellites orbiting the Earth, each carrying an extremely accurate atomic clock and broadcasting the time. Your phone listens to those signals and works out where you are by measuring how long each one took to arrive.
The system was built by the United States military. The first GPS satellite was launched on 22 February 1978, and the constellation of 24 satellites was completed in 1993, with full operational capability declared in 1995. It was designed so that soldiers, ships and aircraft could find their position anywhere on Earth, in any weather. Civilians were allowed to use a less accurate version at first. In 2000, the deliberate degradation of the civilian signal was switched off, and GPS became accurate enough for everyday navigation. Today there are about 31 operational GPS satellites.
Here is how the trick works. Each satellite broadcasts two things: where it is, and what time it is — according to its atomic clock, which loses less than a second in millions of years. Your phone receives the signal and notes the time it arrived. The difference between the sent time and the received time tells the phone how far away the satellite is, because radio waves travel at the speed of light. One satellite gives you a distance. Two narrow it down. With four satellites, your phone can work out its position in three dimensions — latitude, longitude and altitude — by a method called trilateration. It is geometry, done in a fraction of a second.
The catch is the clocks. Your phone's clock is nowhere near as accurate as the satellite's, and even a tiny error in timing becomes a huge error in position: light travels about 300 metres in a single microsecond. So the phone treats its own clock error as a fourth unknown and solves for it along with the position, which is why it needs a minimum of four satellites. More satellites give a better fix. That is why your location is more accurate in an open field than in a narrow lane between tall buildings, where signals bounce and arrive late.
GPS signals are faint by the time they reach you. Anything that blocks the sky makes them worse: tunnels, basements, dense forests, and the concrete canyons of a city. Indoors, your phone falls back on Wi-Fi networks and mobile towers, which is why a mall map can place you in the wrong shop. Weather does not matter much, but solar storms can disturb the signals, and in rare cases governments can jam or spoof them. Your phone copes by combining GPS with other sensors — the accelerometer, the compass, the gyroscope — to guess your movement between fixes.
There is also a quiet issue: privacy. Your phone knows where you have been, and so does every app you granted location access to. That history can reveal your home, your workplace, your doctor, and your habits. GPS itself does not track you — your phone only listens, it does not transmit to the satellites — but the apps on your phone can record and share your location. Checking which apps have location access, and setting them to ask only while in use, is one of the simplest privacy steps you can take.
India did not want to depend entirely on a foreign military system for something as basic as navigation, so ISRO built its own: NavIC, short for Navigation with Indian Constellation. The original design has seven satellites — three in geostationary orbit, staying fixed above the equator, and four in geosynchronous orbit, tracing a figure of eight over India each day. The first satellite went up in July 2013, and the constellation was completed in April 2016 with the launch of IRNSS-1G. NavIC covers India and the region extending about 1,500 kilometres beyond its borders, and it was built to be accurate to a few metres for civilian use.
NavIC is designed for Indian needs: navigation for vehicles and ships, timing for power grids and banks, and disaster management in areas where other signals are weak. Some newer phones sold in India already support it, and the government has pushed for wider adoption. It does not replace GPS for most users yet — it works alongside it, giving your phone more satellites to listen to, which means a faster and more reliable fix. The long-term goal is a system India controls entirely, so that navigation keeps working even if access to foreign systems is ever restricted.
The next time the blue dot finds you, remember what is happening: clocks in space, about twenty thousand kilometres above you, are broadcasting the time; your phone is measuring millionths of a second; and geometry is turning those measurements into a place on a map. It is a military system turned into a public utility, a piece of space infrastructure so reliable that we have forgotten it is there. And that is the highest compliment a technology can receive: to become invisible, and to simply work.
This explainer was written by The Daily Short's desk from the sources listed above. It is general information, not professional advice. Spot an error? Tell us via the Contact page and we will correct it. Follow our official Instagram @the.daily.short.