Measuring the Very Large

For distance that is. The Kilometer

What exactly *is* a kilometer? 1000 meters We walk at about 5 km/hr, or 0.0015 km/s

The Moon (closest object), is 400,000 km away How long to walk there?

Lunar

The distance to the *nearest* planet, Venus 38,000,000 km ▪ (at its closest, but it can be up to 228,000,000 km

away) How long to walk that?

From the earth to the sun is 150,000,000 km This is used as a new unit of distance The Astronomical Unit (A.U.)

Solar

In the solar system: Jupiter is 4 A.U. from us Neptune, 30 A.U. Pluto, 50 A.U. Edge of the solar system, 100,000 A.U. Nearest Star (Alpha Centauri), 268,000 A.U.

Clearly, the A.U. quickly loses its usefulness.

oort

Light travels faster than anything else in the universe. 300,000 km/s (186,000 mi/s, or 670,000,000

mi/hr)

In one year, light will travel 10 trillion km

This is called the LIGHT YEAR (ly)

It is the BASIC unit of distance for astronomy

Loca

l Sta

rs

Nearest Star 4.2 light years

Thickness of the milky way galaxy 1,000 ly

To the center of our galaxy 25,000 ly

Diameter of our galaxy 120,000 ly

Distance to the nearest major galaxy (Andromeda) 2,000,000 ly

• Ultra