Astronomy Cast
Astronomy Cast takes a fact-based journey through the cosmos as it offers listeners weekly discussions on astronomical topics ranging from planets to cosmology.

• Universe grows and cools until 100 seconds after the Big Bang. The temperature is 1 billion degrees, 109 K. Electrons and positrons annihilate to make more photons, while protons and neutrons combine to make deuterons. Almost all of the deuterons combine to make helium. The final result is about 3/4 hydrogen, 1/4 helium by mass; deuteron/proton ratio 30 parts per million. There are about 2 billion photons per proton or neutron.
• One month after the Big Bang the processes that convert the radiation field to a blackbody spectrum become slower than the expansion of the Universe, so the spectrum of the Cosmic Microwave Background (CMB) preserves information back to this time.
• Matter density equals radiation density 56,000 years after the Big Bang. The temperature is 9000 K. Dark matter inhomogeneities can start to collapse.
• Protons and electrons combine to form neutral hydrogen. Universe becomes transparent. Temperature is T=3000 K, time is 380,000 years after the Big Bang. Ordinary matter can now fall into the dark matter clumps. The CMB travels freely from this time until now, so the CMB anisotropy gives a picture of the Universe at this time.
• The first stars form 100-200 million years after the Big Bang, and reionize the Universe.
• The first supernovae explode and spread carbon, nitrogen, oxygen, silicon, magnesium, iron, and so on up through uranium throughout the Universe.
• Galaxies form as many clumps of dark matter, stars and gas merge together.
• Clusters of galaxies form.
• The Solar System and Sun form 4.6 billion years ago.
• Now: The time is 13.7 Gyr after the Big Bang, and the temperature is T=2.725 K. The homogeneous patch is at least 1029 cm across, which is larger than observable Universe.

Even though the universe is now a chilly 2.725 K, it was once much hotter. In fact, from the moment of the initial big bang singularity until nearly 100,000 years later, the universe was hot enough so that electrons and protons had too much energy to come together and form neutral atoms. What existed was a "primordial soup" full of free electrons, protons and neutrons.

One of the most identifiable nebulae in the sky, the Horsehead Nebula in Orion, is part of a large, dark, molecular cloud. Also known as Barnard 33, the unusual shape was first discovered on a photographic plate in the late 1800s. The red glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma Orionis. The darkness of the Horsehead is caused mostly by thick dust, although the lower part of the Horsehead's neck casts a shadow to the left. Streams of gas leaving the nebula are funneled by a strong magnetic field. Bright spots in the Horsehead Nebula's base are young stars just in the process of forming. Light takes about 1,500 years to reach us from the Horsehead Nebula.

From afar, the whole thing looks like an Eagle. A closer look at the Eagle Nebula, however, shows the bright region is actually a window into the center of a larger dark shell of dust. Through this window, a brightly-lit workshop appears where a whole open cluster of stars is being formed. In this cavity tall pillars and round globules of dark dust and cold molecular gas remain where stars are still forming. Already visible are several young bright blue stars whose light and winds are burning away and pushing back the remaining filaments and walls of gas and dust. The Eagle emission nebula, tagged M16, lies about 6500 light years away, spans about 20 light-years

Newborn stars are forming in the Eagle Nebula. This image, taken with the Hubble Space Telescope in 1995, shows evaporating gaseous globules (EGGs) emerging from pillars of molecular hydrogen gas and dust. The giant pillars are light years in length and are so dense that interior gas contracts gravitationally to form stars. At each pillars' end, the intense radiation of bright young stars causes low density material to boil away, leaving stellar nurseries of dense EGGs exposed. The Eagle Nebula, associated with the open star cluster M16, lies about 7000 light years away.

Alex Filippenko is the Richard and Rhoda Goldman Distinguished Professor in the Physical Sciences. His research accomplishments, documented in more than 600 published papers, have been recognized by several major prizes, and he is one of the world's most highly cited astronomers. In 2009 he was elected to the National Academy of Sciences. He has won the top teaching awards at UC Berkeley and has been voted the "Best Professor" on campus six times. In 2006, he was selected as the Carnegie/CASE National Professor of the Year among doctoral institutions.

Most of the Universe is dark. The protons, neutrons and electrons that make up the stars, planets and us represent only a small fraction of the mass and energy of the Universe. The rest is dark and mysterious.

Through his spyglass, in 1609 Galileo saw that there were spots on the Sun, imperfections on the Moon, and that the Milky Way was composed of millions of faint stars. His most stunning (and controversial!) discovery was of satellites orbiting Jupiter, dashing the concept that the Earth was the center of the Universe.  (NASA)

The more I learn about the universe, the less convinced I am that there's any sort of benevolent force that has anything to do with it, at all

-Neil degrasse Tyson

The Universe is Rated R for Cosmic Violence. Since the Big Bang the Universe has been a dynamic mix of exploding stars, colliding galaxies, black holes, dark matter, comets and asteroids- this cosmic violence is on such an immense scale that it makes our tiny planet seem like a distant spectator hoping not to be noticed by the war of the titans. But it will be noticed and has been in the past. There is a huge nuclear fire ball called the sun in our solar system that will become a red giant and the Andromeda galaxy heading towards our own galaxy.

"A general problem with much of Western theology in my view is that the god portrayed is too small. It is a god of a tiny world and not a god of a galaxy much less of a universe."

-Carl Sagan

The gods of the human primate from this little blue planet in the universe seem to be too small, too human and too petty to be the ultimate force in this giant cosmos.


The created gods of the human mind are too small and petty for the grandeur of the stars and universe. Human gods do not even cover the scale of the earth and its history much less the universe.

"A universe in which everything is known would be static and dull, as boring as the heaven of some weak-minded theologians ."
Carl Sagan

"...one of the strongest motives that lead men to art and science is escape from everyday life with its painful crudity and hopeless dreariness, from the fetters of one's own ever-shifting desires. A finely tempered nature longs to escape from the personal life into the world of objective perception and thought."

"A person starts to live when he can live outside himself."

"A human being is a part of a whole, called by us _universe_, a part limited in time and space. He experiences himself, his thoughts and feelings as something separated from the rest... a kind of optical delusion of his consciousness. This delusion is a kind of prison for us, restricting us to our personal desires and to affection for a few persons nearest to us. Our task must be to free ourselves from this prison by widening our circle of compassion to embrace all living creatures and the whole of nature in its beauty."

"Now he has departed from this strange world a little ahead of me. That means nothing. People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion."

"Imagination is more important than knowledge."

"We can't solve problems by using the same kind of thinking we used when we created them."

"Education is what remains after one has forgotten everything he learned in school."

"The important thing is not to stop questioning. Curiosity has its own reason for existing."

Albert Einstein

"We are just an advanced breed of monkeys on a minor planet of a very average star. But we can understand the Universe. That makes us something very special."

"It surprises me how disinterested we are today about things like physics, space, the universe and philosophy of our existence, our purpose, our final destination. Its a crazy world out there. Be curious."

Stephen Hawking