We urbanites are so trapped in our mundane engagements that we are rarely aware of the celestial sphere at night 鈥� and there is not much to see in the first place.

But our ancestors used to look above long and steady for portents of future events.

In 1054, they noticed a new star (鈥済uest star鈥�) in the constellation Taurus. It was visible for many weeks, even during the day.

They were witnessing a supernova explosion whose expanding remnants are still visible today, according to 鈥淲elcome to the Universe,鈥� a guided tour of the cosmos by three leading astrophysicists, Neil deGrasse Tyson, Michael A. Strauss and J. Richard Gott.

Even though such cosmic events were not predictors of human fate, we should not underestimate their relevance to us. As explained in the book, the hydrogen in our body was forged in the birth of the universe itself, while the other heavier elements originated from distant, long-dead stars.

The mysteries of the universe concern us in other ways.

鈥淒id you know there is an ultimate limit to how much information can ever be stored in a 6-inch-diameter hard drive and that depends on black hole physics?鈥� Gott observes. Black holes take us to the frontiers of astrophysics, but this book does not presuppose a solid grounding in science.

The book has been inspired by the enormously popular introductory astronomy course for nonscience majors at Princeton University, a course that was commended in the Time magazine.

In an informative and entertaining way, the book takes us from the latest discoveries to the edge of outer space, from planets, stars, galaxies to black holes, wormholes, and time travel.

The awesome universe makes you feel tiny and insignificant at times, but the book has been written to empower.

The cosmos can be stunning in purely numerical terms. For instance, a thimbleful of neutron star material equals a herd of 100 million elephants.

Our traditional conception of the universe as everlasting and unchanging (tianchang dijiu) is also challenged, as equation traces the beginning to the Big Bang 13.8 billions years ago, when all the space, time, matter, and energy were crushed together in a hot, seething cauldron of matter and energy.

We were born in the Big Bang, and as the universe expanded in the one-way expansion, the temperature cooled to about 2.7 K today. It will cool further, until it bottoms out at a temperature predicted by Stephen Hawking.

And then one by one the light of the stars dies out, and darkness reigns.

Intriguing, but the crux of the matter is how to explain fundamental scientific principles to common readers.

Elemental truth

The book reasons that the sun鈥檚 visible light is not absorbed by the air, because otherwise you would not see the sun at all.

You cannot see the sun in a room without windows, because the roof of your building is absorbing the visible light from the sun.

The ground absorbs the light from the sun, and then radiates the energy back to the atmosphere as invisible infrared light which can be absorbed by the air (and heating the air). This is easy to understand.

When this topic is further pursued, we learn that the ground behaves as a blackbody, or an object that absorbs all incident radiation. Same with your body. What鈥檚 your body鈥檚 luminosity, or wattage?

The answer is that on average each of us functions as a light bulb of 900 watts. Hence the need to metabolize food to keep the light on. But with the sun a very violent process is going on to maintain its luminosity.

In the center of the sun, at 15 million K, 4 million tons of matter needs to be converted into energy every second.

When Einstein came out with the famous equation in 1905, E = mc2, which shows that a certain amount of matter can be completely converted into energy, it was realized that the sun is one big thermonuclear fusion bomb, except that its awesome energy is contained by all the mass pressing down on the core.

The equation led to the creation of nuclear bombs.

Most nuclear bombs exploded in the Cold War were fission bombs, while today most power of our nuclear arsenal are fusion bombs.

To give you a sense of how destructive they are: Fusion bombs use fission bombs as their trigger. The bombs make us uneasy, but it is fascinating to know how this process is actually linked with our own makeup, and our fate.

With higher temperature and pressure, helium fusion kicks in, leading to carbon, and then to oxygen at the core. By following a similar process, you get iron in the middle, surrounded by successive shells of lighter elements.

And when iron accumulates, it is the end of the road. For if you fuse iron, instead of getting energy, the process would suck the energy out of the star. The fusion stops, and the star collapses.

鈥淎s the core collapses faster and faster, the star implodes, leaving a tiny, superdense neutron star in the center, whose formation generates enough kinetic energy to blow off the entire envelope and outer core of the star and causes a titanic explosion, for several weeks shining billions of times brighter than the sun,鈥� Tyson explains. 鈥淏ut these elements are still locked inside a star, and they have to get out of the star somehow, because we鈥檙e made of these elements!鈥�

The guts of this star are now released into the galaxy, into what we call the interstellar medium, chemically enriching gas clouds with heavy elements, enabling gas clouds to become something more interesting than clouds of pure hydrogen and helium.

Interesting, because some of these heavier elements end up in our body. As Strauss concludes: 鈥淚t鈥檚 both humbling and awesome to realize that most of the material in our bodies and everything that surrounds us has been produced through thermonuclear processing in stars.鈥�

Einstein鈥檚 time travel to the past can be hard to understand, but it is easier to see telescopes are time machines that 鈥渟how us the distant past and allow us to study the processes by which galaxies evolve through cosmic time.鈥� By comparing the properties of distant galaxies with those we see in the nearby universe, we can gain insight into how galaxies are formed.

The book鈥檚 explanation of the Big Bang is also revealing.

When the universe was born 鈥� time, space, energy and all 鈥� it appears to have been infinitely dense and infinitely hot. Was it also infinitely small? Think about what we mean by 鈥渟mall.鈥� The universe is infinite in size today, and expanding, thus shrinking it in the past still leaves it infinite in size, and that was true all the way back to the Big Bang.

This makes it easier for us to make sense of the appropriate equations of Einstein鈥檚 theory of general relativity.

Destructive know-how

鈥淭he Big Bang was not an explosion, as it is sometimes erroneously depicted, of something very small and dense expanding into empty space. It is not like a bomb. Because the universe has no edge, there is no empty space 鈥榦ut there鈥� for it to expand into. It is the space itself that is expanding,鈥� explains Strauss.

It is also observed that 鈥渨hat existed before the Big Bang鈥� is a legitimate question, only that general relativity doesn鈥檛 have an answer for you.

鈥淭he equations of general relativity predict an infinite density at the moment of the Big Bang. In science, when your equations yield a result of infinity, you know that your theory is incomplete; there is more physics going on than the equations describe,鈥� writes Strauss.

But a host of observations accord beautifully with the theory.

鈥淭he Big Bang model is far more than 鈥榡ust a theory鈥�: it is supported by a vast array of empirical, quantitative evidence and has passed every test we have given it with flying colors,鈥� writes Strauss.

Tyson observed that we should feel empowered and emboldened for our understanding of astrophysics, 鈥渂ecause the human brain, our three pounds of gray matter, figured this stuff out.鈥�

Our uncanny cognitive power should also make us tremble. Robert Oppenheimer, the leader of the Manhattan Project, later said that the first test of the atomic bomb reminded him of lines from the Bhagavad Gita: 鈥渘ow I am become Death, destroyer of worlds.鈥�

In Truman鈥檚 private library, a book on the atomic bomb was found where he had underlined words from Horatio鈥檚 last speech in Hamlet: 鈥淟et me speak to the unknowing world. So shall you hear of carnal, bloody and unnatural acts, of accidental judgments, casual slaughters, of deaths put on by cunning and forced cause, and, in this upshot, purposes mistook fall鈥檔 on the inventors鈥� head.鈥�