It is not completely empty.
It is a hard vacuum containing a low density of particles,
predominantly a plasma of hydrogen and helium,
as well as electromagnetic radiation, magnetic fields,
neutrinos, dust, and cosmic rays.
- FAI – The International Aeronautical Federation, recognises the Karman line 60 miles above Earth’s surface as being the boundary between the atmosphere and space.
- local space is known as the region around of our Solar System.
- space is not an empty vacuum – it is a near vacuum; each cubic kilometre contains a few drifting atoms of gas and dust.
- in the region of our Sun – this interstellar medium consists of about 90% hydrogen, 9% helium and 1% dust.
- interstellar dust – tiny grains composed mainly of silicate (silicon and oxygen) and graphite (carbon) as well as small amount of iron.
- between galaxies – intergalactic medium consists mostly of ionized hydrogen – atoms of hydrogen gas that have had their electron stripped away.
How do we measure the distances to things in space?
- space is so big – that miles becomes meaningless!
- so that’s why people often use the word ‘astronomical’ to describe exceptionally large number instead.
- in local distances are often measured in AU (Astronomical Units); one AU is around 92 million miles as the average distance between the Earth and the Sun. (diagram)
- interstellar space – usually measured in light years (ly); one light year is about 5.6 trillion miles (the distance light travels in one year.)
- some astronomers prefer to measure large distance in parsecs (pc); one parsec equals 3.36 light years .
.Back to Exploring Space page.