How fast is Earth spinning where you live in India?
Everyone in India is moving at well over 1,000 km/h without feeling a thing. We calculated the speed for each city, then added Earth’s orbit, the Sun’s path around the galaxy, and what all that does to your weight.
Earth’s rotation carries you eastwards at about 1,471 km/h if you live in Delhi, 1,583 km/h in Mumbai, 1,631 km/h in Chennai and 1,658 km/h at Kanyakumari. At the equator the speed is 1,674 km/h, about 465 metres every second. The farther you are from the equator, the smaller the circle you travel each day and the slower you go, so Srinagar moves at about 1,388 km/h.
How fast does the Earth rotate?
Earth turns once on its axis, relative to the distant stars, every 23 hours 56 minutes and 4 seconds. That is the sidereal day. The 24-hour day we live by is about four minutes longer, because Earth also moves along its orbit each day and has to turn a little extra to bring the Sun back to the same place in the sky.
A point on the equator, 6,378 km from the axis, covers a circle of 40,075 km in one sidereal day, which gives 465 metres per second. Away from the equator the circle shrinks. In Delhi, at 28.6 degrees north, you are about 5,600 km from the axis and your daily circle is about 35,200 km long. Earth is slightly flattened, so we used the standard WGS84 model of its shape for each city rather than a perfect sphere.
Why don’t we feel Earth spinning?
You feel changes in motion, not motion itself. In a smooth aeroplane at 900 km/h you can pour tea; what you notice is take-off, turbulence and braking. Earth’s spin is extraordinarily steady, and the air, the oceans and you all share it. The only acceleration involved is the gentle inward pull needed to keep you on a circle, about 0.034 metres per second squared at the equator. That is a third of one percent of gravity: real, measurable, and far too small to feel.
You weigh slightly less in Kanyakumari
That small effect does show up on precise scales. Spin and Earth’s bulge together make gravity a little weaker near the equator. Using the standard formula for gravity at sea level and allowing for each city’s height, we find that a person whose weight reads 70.000 kg on a spring scale in Delhi would read about 69.927 kg in Kanyakumari, 69.939 kg in Chennai and 69.959 kg in Mumbai. That is about 70 grams lighter in Kanyakumari. Your mass is the same everywhere; only the pull on it changes. A balance scale, which compares masses, would show no difference.
Rockets use the spin: why ISRO launches east
A rocket launched eastwards starts with the ground’s speed for free. At Sriharikota, 13.7 degrees north, that is about 452 m/s; at Baikonur in Kazakhstan it is about 324 m/s, and at Cape Canaveral about 409 m/s. That bonus is one reason launch sites are placed as close to the equator as a country allows and why ISRO launches geostationary satellites eastwards over the Bay of Bengal. Our story on why India is building a second spaceport in Tamil Nadu explains why the new site is chosen for southward launches instead.
And faster still: Earth’s other motions
- Around the Sun: about 30 km per second, or roughly 107,000 km/h. Earth moves fastest when closest to the Sun, at perihelion on 3 January 2027, at about 30.3 km/s, and slowest at aphelion on 5 July 2027, at about 29.3 km/s.
- Around the Milky Way: the Sun carries the whole solar system around the galaxy at roughly 230 km per second, taking more than 200 million years for one lap.
- Relative to the cosmic microwave background: the slight warming of that afterglow of the Big Bang in one direction of the sky shows the solar system moving at about 370 km per second relative to it.
Is Earth’s rotation slowing down?
Yes, very gradually. The Moon’s tides act as a brake, and over centuries the day has lengthened by about 1.8 milliseconds per century on average, according to a study of ancient eclipse records by Stephenson and colleagues in 2016. Over shorter spans the spin speeds up and slows down by fractions of a millisecond as the atmosphere, oceans and Earth’s core shift; in recent years it has run slightly fast, which is why timekeepers have discussed, for the first time, a leap second that would be removed rather than added.
How we worked this out
Rotation speed is 2π times the distance from Earth’s axis, divided by the sidereal day of 86,164.09 seconds. The distance from the axis uses the WGS84 ellipsoid (equatorial radius 6,378.137 km, flattening 1/298.257) at each city’s latitude. Gravity uses the Somigliana normal gravity formula for WGS84 with a free-air correction of 0.3086 mGal per metre for each city’s approximate height above sea level. Orbital speeds and the dates of perihelion and aphelion come from the open-source Astronomy Engine library. Launch-site speeds use the same rotation formula. The galactic and cosmic microwave background speeds are rounded published values.
Sources
- US National Geospatial-Intelligence Agency: World Geodetic System 1984
- Stephenson, Morrison and Hohenkerk (2016): measurement of the Earth’s rotation, 720 BC to AD 2015
- Planck Collaboration (2018): Planck 2018 results I, overview (CMB dipole)
- NASA: EPIC, Earth Polychromatic Imaging Camera
- Astronomy Engine, open-source astronomy calculation library
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