Science
Science
Physics, chemistry and the measurements behind everyday things, from light and air to the constant that now defines the kilogram.
Fact files
All topics ›Earth's atmosphere
78.08 %
Nitrogen in dry air, by volume
X-rays
8 November 1895
Evening Röntgen saw a screen glow across his darkened room
The kilogram
1889
Year the metal cylinder was sanctioned as the unit of mass
Rainbows
40 to 42 degrees
Angle of the primary bow from the antisolar point
Gravity
9.80665 m/s²
Standard acceleration of gravity, an exact defined value
Helium
1868
Year helium was first detected, in the Sun's spectrum