The UniverseThe Universe

Seconde F

Order of MagnitudeOrder of Magnitude

Order of MagnitudeOrder of Magnitude

1 Gm = 1 gigameter = 10^9 meters = 1 000 000 000 m1 nm = 1 nanometer = 10^(-9) meter = 0.000000001 m

Order of MagnitudeOrder of Magnitude

Nucleus of an atom

nucleus

AtomBacteriaHumansEarthSunSolar System

Interstellar distanceGalaxyObservable universe

1000 kg 1 Kg

Order of MagnitudeOrder of Magnitude

Filling of space by the matter is essentially incomplete, at both tiny (atom) and big

(cosmos) scales (essentially void around us)

Speed of lightSpeed of lightSpeed of light in vacuum is a phyical constant : c = 3.10^8 m/s = 300 000 000 m/s The light is composed of photons and is propagated in straight line

Speed of light (speed of propagation) depends only on the medium

speed(vacuum) = speed(air) = c = 3.10^8 m/s

speed(water) < cRefraction index n : quantity without

unit

A.Einstein 1879 - 1955

Speed of lightSpeed of lightGalilée, Romer, Cassini, Newton,

Michelson.. using astronomy The meter is the distance travelled

by the light in the void during 1/299 792 458 second

v = c (m/s)

m

s

Speed of lightSpeed of light

d = 1m

d = 150 000 000 Km

Even if the light of speed is great, the gigantic distances at the cosmos scale cause delays (we don’t

see things in ‘real time’)

s m

m/s

s km

km/s

Light-yearLight-yearA light-year is the distance travelled

by the light in vacuum during one year

The light-year (ly) is not a new unit, it’s used only because it’s handy with the gigantic distances we

have in the cosmos

m

m/s

s

1 year converted in seconds

1 ly

roughly

Light-yearLight-year

I see dinosaurs

How far are we from this planet?Extinction of the

dinosaurs : 65 millions years ago

The aliens are at least 65 000 000 light-years away from us

Watch far = Watch in the past

Light-yearLight-year

Questions ?

Homework