2009: International Year of Astronomy

Look
Creative Commons License photo credit: judepics

We could say that modern astronomy began in 1609.  That was the year when the telescope, invented by the Dutch in 1608, was first used to observe and describe celestial objects.  Until telescopes were used, astronomy was primarily about measuring the positions of the Sun, Moon, and planets in the sky.  This helped early astronomers make calendars and to plan their harvests, but people were unable to study the celestial bodies and learn their characteristics.  A recently discovered lunar map indicates that Thomas Harriot of England was the first to observe and draw a magnified image of the Moon in July 1609. 

Galileo Galilei, of course, is most well-known for building and using early telescopes.  He did his lunar observations in December 1609 while observing from Padua, Italy.   The prevailing idea at the time was that everything in the heavens had to be perfect and unblemished.  Drawings of mountains, valleys, and craters on the Moon contradicted this idea, showing the Moon to be an ‘imperfect’ world like Earth.  As Galileo published his drawings and Harriot did not, Galileo gets the credit for changing our concept of the universe, helping us realize that celestial bodies are worlds and not just sources of light.

On January 9, 1610, Galileo saw three ‘fixed stars’ next to Jupiter.  Four days later he discovered a fourth and realized that these ‘stars’ orbited Jupiter.  Today, those four moons– Io, Europa, Ganymede, and Callisto, are called the Galilean moons.  The direct observation of moons orbiting Jupiter disproved Claudius Ptolemy‘s model of the universe, already centuries old at the time, which held that all bodies in the universe orbited the Earth.

Moon n Venus played hide-and-seek
Creative Commons License photo credit: voobie

In December 1610, Galileo observed Venus and saw that Venus showed phases like the Moon’s when magnified in his telescope.  This meant that sometimes the sunlit side of Venus faces Earth, while at other times we see the night side, although Venus is never opposite the Sun in the sky.  This could happen only if Venus orbits the Sun rather than Earth.

By the way, Galileo did far more than just astronomy.  Rice University’s Galileo Project has more on his extraordinary life, including a timeline.

It was also in 1609 that Johannes Kepler published his New Astronomy, containing his first two laws.  The first law states that each planet’s orbit is an ellipse rather than a perfect circle.  The second law states that a planet sweeps out equal areas in equal times.  Kepler published his third law, which relates the square of a planets period (time for one orbit) to the cube of its average distance, in 1619. 

This makes 2009 the 400th year of modern astronomy.  Appropriately, the United Nations declared this year to be the International Year of Astronomy.  At that link, you can learn about events taking place all over the world promoted by the International Astronomical Union (IAU) and the United Nations Educational, Scientific, and Cultural Organization (UNESCO).  Their goal is for people all over the world to discover the wonders of the sky and to appreciate our place in the universe.

Star Cloud Over Saskatchewan.jpg
Creative Commons License photo credit: Space Ritual

You can participate in the International Year of Astronomy right here in Houston.  Several of the Fun Hundred events we’ve set up to celebrate our 100th anniversary are astronomy-related.  They include Sun-Earth Day at the vernal equinox, our annual viewing of the Perseid meteor shower in mid-August, members nights at the George Observatory, and a winter solstice event on our sundial. 

Also, you can observe the phases of Venus in the first three months of this year, just as Galileo did through his telescope.  Keep in mind that Galileo’s telescope looked like this; anyone with a good pair of binoculars has better observing equipment.  Go outside at dusk and look west southwest for the brightest point of light in the sky.  That is Venus.  Through a telescope, you’ll notice that Venus appears half-lit in mid-January 2009.  As you keep observing through March, you’ll see Venus become a more and more pronounced crescent.  This is because Venus is coming around to our side of the Sun and thus turning more and more of its night side to Earth.  The very skinny crescent of mid-March is so pronounced that it is noticeable in binoculars.

Remember, the great discoveries, or aha moments, as my co-blogger described, are not limited to great, historic scientists.  The beauty of science is that anyone who takes the time to observe can share in the act of discovery.

The Great Cosmic Year

Our Milky Way Galaxy..
Creative Commons License photo credit: Sir Mervs

One of the biggest challenges in teaching astronomy to kids – or even to the general public – is that astronomy involves numbers so big as to be virtually meaningless. Consider the age of the universe, for example. Our best data indicate that the Big Bang, where space and time began, occurred about 13.7 billion years ago. As very few of us have seen 13.7 billion of anything before, how can we appreciate how long a time that is?

One way is to use a scale-model. Just as we use globes because the real Earth is too big to look at, we can ‘shrink’ the 13.7 billion year history of the universe into one year. Imagine a Great Cosmic Year, in which the Big Bang occurs at 12:00:00 am on January 1 and the present moment is 11:59:59.9999999 pm on December 31. On this time scale, each day represents (13.7 billion/365) years, or about 37.5 million years. Our best estimates for when the events listed below occurred are approximate; the dates listed may need to be adjusted slightly in the future.

Still, locating the events in the history of the universe, the Sun, and the Earth on this calendar can give us a better sense of how much time is involved.

January 1, midnight The Big Bang occurs.

January 13 The oldest known star in our galaxy (designated HE 1523-0901) forms.

‘HE’ here refers to the Hamburg/ESO (European Southern Observatory) survey, in which the star is catalogued. Being about 100 times too dim to be seen with the unaided eye, the star has no common name. It is in the constellation Libra.

Planet Earth (III)
Creative Commons License photo credit: Aaron Escobar

January 4-27 Re-ionization occurs.

We take for granted that the universe is transparent; that we can look through space and see galaxies, stars, and other planets. However, once hydrogen atoms formed in the early universe, this would have been impossible, as hydrogen atoms readily absorb photons (light particles). After the first billion years (corresponding to January 27 in the Great Cosmic Year), the hydrogen had been re-ionized. This happens when the electron in the hydrogen atom is too energetic too remain in orbit around the single proton which makes up the hydrogen nucleus. Newly formed stars and galaxies provided much of this energy.

April 14 First Sun-like stars (population I) appear.

Hydrogen and helium are so abundant in the universe that astronomers lump all other elements into a catch-all category called ‘metals.’ Astronomers divide stars into three categories based on their ‘metallicity,’ or how much stuff other than H or He they contain. This is important because those ‘metals’ ultimately make up solid things such as planet Earth, or you or me. Our Sun is only about 2% ‘metal.’

Stars of comparable metallicity are the youngest and are placed in population I. Some older stars in the distant halo of our galaxy are much less ‘metallic’ than our Sun, in some cases by a factor of 1,000 or 10,000; these are population II stars. Since all elements heavier than helium are formed in stars, astronomers speculate that the very first stars had virtually no metals, but such ‘population III’ stars have yet to be discovered.

It took about four billion years to make the first population I stars, bringing us to April 14 in our Great Cosmic Year.

Andromeda, again.
Creative Commons License photo credit: makelessnoise

May 23 The Milky Way’s galactic thin disc forms. This part of our galaxy includes our Sun.

August 31 Our solar system forms from a spinning cloud of dust.

The first population I stars to formed back on ‘April 14′ did not include our Sun. Astronomers recently discovered decay products of 60Fe, an isotope of iron that results from supernovae (exploding stars), in some meteorites. This suggests that a nearby supernova ejected this material into the dust cloud that became our solar system, making our sun at least a second generation population I star.

September 2 Earth begins to form.

Bad Moon Rising
Creative Commons License photo credit: makelessnoise

September 3 The Moon forms when a Mars-sized object called ‘Theia’ strikes Earth.

September 21 Earth begins to solidify.

This corresponds to the end of the Late Heavy Bombardment, a period of frequent impacts on all bodies in the inner solar system. Up to this point, consistent bombardment kept the Earth molten, with magma seas. With the end of the bombardment, Earth began to cool, solid rocks appeared, and Earth’s geologic history began.

September 29 Life begins on Earth.

October 12 The first continent (called Ur) appears on Earth.

November 2 Oxygen (O2) builds up in Earth’s atmosphere.

November 14 Eukaryotes (with distinct nuclei in the cell) exist on Earth.

November 27 Multicellular organisms exist.

December 5 The supercontinent Rodinia forms.

December 17 Cambrian explosion: earliest forms of most types (phyla) of animals appear.

December 20 First life on land

triceratops
Of course, the real dinosaurs were bigger,
and not made of paper.
Creative Commons License
photo credit: kekremsi

December 25-29 Age of the dinosaurs

December 30 (morning) Chicxulub meteor impact helps cause extinction of about 3/4 of all life, including the dinosaurs.

The following events all occur on December 31:

9:17 am Drake passage completes the isolation of Antarctica; the continent freezes over.

7:30 pm Human ancestors diverge from chimpanzees.

9:57 pm Lucy lives in east Africa.

11:52 pm Homo sapiens sapiens exists.

11:59:14 pm Last Glacial Maximum (most recent Ice Age)

11:59:45pm Uruk, in Sumer, is one of the first cities on Earth.

Our existence as a species, compared to the whole universe, is about eight minutes out of a year. All of human civilization amounts to about 15 seconds. Once, I presented this calendar and was told that the smallness of our existence was an attack on religious faith. Perhaps, however, this need not be so. After all, an important virtue in most religious traditions is humility. This is not the denial of our talents and value, but the realization that we, with our goals, hopes, and dreams, are but one element of a much larger whole. As you reflect back on 2008 this holiday season, I invite you to reflect on the Great Cosmic Year. I find that the resulting wonderment and awe deepens my appreciation of the universe, and reminds me why I studied science in the first place.