| Nature is a temple where alive pillars |
|---|
| Sometimes let leave confused words; |
| The man passes there through forests of symbols |
| Who observe it with familiar glances. |
| As long echoes which by far merge |
| In dark and deep unity, |
| Vast like the night and clearness, |
| The perfumes, the colors and the sounds are answered. |
| It is fresh perfumes like flesh of children, |
| Soft like the oboes, greens like the meadows, |
| - And others corrompus, rich person and triumphing, |
| Having the expansion of the infinite things, |
| Like amber, musk, benzoin and incense |
| Who sing transport of the spirit and the directions. |
| Charles Beaudelaire in Correspondences |
We present in this chapter the various types of measurement of distance in cosmology. In particular, we present how the measurement of the distance from luminosity makes it possible to force the cosmological parameters presented at the first chapter.
We present, in the second time, how in practice the measurement of distance is carried out. In particular, we describe how measurements of the flux of objects whose intrinsic luminosity is known (standard candles) allows measurements of distances.
Lastly, we present the various observational difficulties which arise in practice to measure distances.
Corrections of extragalactic extinction