The visible and the invisible

The spectrum of the Sun and the sensitivity of the eye. away, to become a mere length, as are all the colours we know and love and with them even those that escape human perception, such as X rays and gamma rays. Light is thereby bleached. In its extended meaning, colour is now a number with units of length, frequency (like our own pulse) or energy. These three physical ideas, spatial, temporal and energetic, are canonically and invariably related. It is a simple matter to translate...

Last dash before oblivion

Onion Skin Structure Massive Stars

The destiny of stellar species invites the following question what mutation transforms an otherwise peaceful and long-lasting celestial body into an explosive and creative supernova In fact it is the star's luminosity and the ruinous energy expenditure of its glorious years that bring about its own downfall. Indeed, to shine it must burn, and to burn it must perish. In a struggle to draw out their final lustre, massive stars push their fires to the very limit and exhaust themselves in an...

MPoO ooo

Hydrogen Fusion

Hydrogen fusion via the proton-proton chain. Fig. 5.1. Hydrogen fusion via the proton-proton chain. Number one is hydrogen, with one proton, whilst four is helium, with two protons and two neutrons. Four protons fuse together under the influence of heat to give a helium nucleus, and this happens billions of times over. The mass of the helium nucleus is slightly less than the sum of the masses of the four protons. What has happened to the difference In fact, it has been radiated away....

History of the Sun Nebulous birth

The sky is no empty arena and stars are not the only actors. The other player in the cosmic drama is the cloud. The business of the perfect interstellar cloud is to confiscate or at least filter the light of stars lying behind or even within it. Certain clouds referred to as bright nebulas are lit up from within. They are in the process of giving birth to a generation of stars, for like rats, cats and fish, stars are born in broods. Hence, the large, dusty and icy interstellar clouds are not...

Supernova dust

Held in meteorite magmas, we find grains or granules called chondrules, whose compositions deviate from the average. Indeed, they exhibit isotopic anomalies with respect to the canonical abundance table. These tiny inclusions represent genuine mineral relics from the stellar age. Although the greater part of the matter in the Solar System displays a high degree of isotopic homogeneity, which is just what allows us to build up the abundance table discussed earlier, a small fraction of this...

Astronomy of radioactivity

The best illustration of radioactive astronomy is titanium-44. We shall take it as the archetype of a good radioactive isotope. It is relatively abundant and has a reasonable lifetime of around 100 years, neither too long, nor too short. Only aluminium-26 can rival it in this respect and nuclear gamma astronomy has already reaped some of the rewards (see Fig. 4.4). Calcium-44 bears the same relation to titanium-44 as a grandson to his grandfather. The radioactive affiliation is Fig. 4.4....

The Sun as reference

The motions of the Sun and Moon form the basis of our calendars. The measurement of mechanical time is largely based on the periodic reoccurrence of certain phenomena the rhythm of day and night, the seasons, or the cyclic reappearance of the planets and stars in the sky. The flow of change is attested by the apparently irreversible global evolution of the Cosmos. Cosmic time, eternity's yardstick, is the measure of universal change, of the evolution of matter, and this evolution is essentially...

Synopsis of nucleosynthesis

Like chemistry, nuclear astrophysics is a combinatorial art. Nuclear reactions are written down like chemical reactions, replacing atoms with nuclei. The earliest nucleosynthesis belongs to cosmology. A first flurry of nuclear reactions took place in the great primordial heat occurring between 1 and 100 seconds after the Big Bang. The species H, D,3 He, 4He and 7Li were synthesised in proportions that depend on the baryonic density of the Universe (Vangioni-Flam & Casse 1998) (see Appendix...

Telescopes in the sky on the ground and in the basement

The air renders us insensitive to radiation from space, some forms of which are lethal, rather like a skin-protecting cream. At the same time it acts as a censor with regard to the astronomical information carried by that radiation. There is no choice therefore but to break out from the cocoon, to rise above the atmosphere by means of stratospheric balloons, rockets and satellites. With its airborne and space-borne telescopes, the whole planet Earth is turned towards the Universe, its eye...