2009: International Year of Astronomy

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.

Go stargazing! July edition

Creative Commons License photo credit: KingArthur10

Jupiter is up all night long this month. At about 3 am on July 9, the Earth will pass between the Sun and Jupiter. This alignment is called opposition because it puts the Sun and Jupiter on opposite sides of the Earth.

Being opposite the Sun in our sky, Jupiter rises at sunset and sets at sunrise; it is up literally all night long the night of July 8-9 and up virtually all night for the whole month. Jupiter outshines everything else in the night sky this month unless the moon is present.

Jupiter is easy to find this July; it is low in the southeast at dusk or low in the southwest at dawn.

Mars and Saturn are also visable this month. Look west at dusk to find stars in the shape of a backwards question mark.  These form the mane of the constellation Leo the lion.  The point under the question mark is Regulus.

Saturn is to Regulus’ upper left.  On July 1, Mars is to the lower right of Saturn, near Regulus.  Saturn is the brighter of the two; Mars continues to fade each day as Earth pulls away from it. Watch each night as Mars approaches Saturn and passes it on July 10. By the end of July, Mars will be up and to the left of Saturn, and both will be lower to the horizon at dusk. The Moon is near Mars and Saturn on July 6th. Venus is lost in the Sun’s glare, and will remain out of sight through the end of the summer.

International Space Station & Half-Moon & Saturn & Regulus
Creative Commons License photo credit: scyllarides

The brightest star in the sky tonight is Arcturus, which you can find by extending the arc of the Big Dipper’s handle (arc to Arcturus).  Arcturus, the fourth brightest star we see at night, is the brightest star left since the top three are not visible in Houston in July.

The Big Dipper happens to be to the upper left of the North Star at dusk this month.

Scorpius, the Scorpion, is in the southeast at dusk.  Sagittarius, the Archer, known for its teapot asterism, is to Scorpius’ left.

 In the east, look for the enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair. This triangle is up all night long in July, hence its name.

Of the three Summer Triangle stars, Vega is the brightest (in fact, 5th brightest overall and 2nd only to Arcturus on July nights). However, Deneb actually puts out far more light, despite the fact that Deneb is about 3000 light years away, compared to 25 light years for Vega.  Star brightness depends not only on intrinsic power, but on distance.

Moon Phases in July 2008:

New July 2, 9:19 pm
1st Quarter July 9, 11:34 pm
Full July 18, 2:59 1m
Last Quarter July 25, 1:42 pm
Full Moon
Creative Commons License photo credit: Andréia

At about 3 am on Friday, July 4, 2008, the Earth is at aphelion (greatest distance from the Sun). We were closest to the Sun about six months ago, on January 2.  This serves as an excellent reminder that it’s the Earth’s tilt on its axis, and not its varying distance from the Sun, which causes our seasons.

Astronomers define the average Earth-Sun distance (about 93 million miles) as one astronomical unit, or AU. On July 4, we will have moved out to 1.016 AU, while on January 2 we were at 0.983 AU. This is not enough of a difference to affect how much warmth comes our way; it’s going to stay hot and sticky for a while.