Thursday, January 17, 2008

Walking With Galileo

Reader Steve Welch asks, “What can be done with the department store telescope that a well-meaning but clueless parent or grandparent (who didn't read your blog) gave someone for Christmas? I think the kids who get those scopes should be helped.” Excellent question, Steve. My diatribe against department store telescopes notwithstanding, the reality is that thousands of small, cheap refractors are given as first telescopes. They can, in fact, be the instruments that spark many a life-long interest in observational astronomy.


If you’ve received one of these, you have a great advantage: you now have a tool to take you beyond the naked-eye stargazing that you’re probably already doing. And I must confess you also have a great advantage over me. In my science-bereft youth, I never saw a telescope and never even knew that a regular person was allowed to own a telescope. Telescopes were big, fancy, complicated pieces of equipment restricted for use by professional scientists in observatories. Or so I thought.

So, where in the Milky Way shall we go? Your new spyglass is probably best suited for exploring our galactic ‘hood, better known as the solar system. You can use it to examine the Moon and the planets. You can even go beyond the solar system and explore the band of the Milky Way. And you’ll be in great company as you do so, because you’ll be walking with Galileo.

We’ve all heard of Galileo Galilei, the 17th century Italian astronomer and “father of modern astronomy” who butted heads with the Catholic Church. Every stargazer who strives to see more through binoculars or telescopes, every amateur telescope maker who grinds glass, every artist who sketches sunspots or moon craters at the eyepiece--they all walk in Galileo’s footsteps. He was the big kahuna who got this star party started.

Galileo Facing the Roman Inquisition - painting by Cristiano Banti

Just one year after the invention of the refractor telescope, the enterprising do-it-yourselfer Galileo turned one of his own improved instruments skyward. He was the first person to use a telescope to make a set of astronomical observations. He quickly made a series of remarkable discoveries, and science and humankind would never be the same.

Galileo was just getting warmed up when he discovered:
- the surface of the Moon is pockmarked with craters. Before Galileo, everyone thought the Moon was smooth, the way bodies in a ‘perfect’ universe should be.
- planets are discs, not points of light like the stars. Before Galileo, planets were thought to be a special type of star: “wandering stars” that moved against the backdrop of the fixed stars.
- the Milky Way is a horde of stars too numerous and faint to be resolved with the naked eye. Before Galileo trained his telescope on it, the long arm of the Milky Way that stretches across the sky could only be seen as a hazy band of light, so its nature was not known.

What makes these and a host of other discoveries truly amazing is that Galileo did it with what we would consider a substandard instrument. Galileo’s telescopes were long, skinny affairs, around four feet long and around two inches in diameter. Only the center of the two-inch glass objective (the optical lens) was usable, due to the primitive glass-grinding techniques of the day. Looking through his telescope would have been a bit like looking through a drinking straw: the field of view was quite small, about a quarter of the Full Moon. It is believed he only ever achieved 20x magnification with the telescopes he made. Additionally, the glass of Galileo’s time was green, due to a high iron content; this was probably a bit like looking through the bottom of an old-time glass Coca Cola bottle. To add yet another challenge to early telescopic viewing, the glass was full of little bubbles.



One of Galileo's telescopes
in the Institute and Museum of the History of Science, Florence, Italy




Sadly, Galileo ended his days confined to his house, because of his conflict with the Church. Moreover, he was nearly blind, probably due to glaucoma (an eye disorder that damages the optic nerve).

This week, let’s send our thanks back across the centuries to the great observer, in the only way that is fitting: by pointing our little refractors at the night sky. No matter how cheap or rinky-dink your telescope is, remember it’s giving you a better view than our pioneering pal Galileo had.


1) The moon will be a great target this week, as it grows towards Full Moon on January 22. It will be already visible in the sky at sunset every evening until January 23, when it will rise about an hour and a half after sunset. Even in my $20 drugstore refractor, the Moon is a marvel of ridges, dark lava seas, and craters of every size.



2) High in the eastern sky at sunset, the red planet Mars shines bright between the two horn stars of Taurus, east of the Pleiades. A view through your little refractor with your highest power eyepiece (lowest mm number) will clearly show the contrast between the disc shape of the planet and the pinpoint lights of the background stars. On Saturday the 19th, the Moon and Mars will dog each other across the sky, a mere sliver apart.


The Winter Milky Way, marked with gray band

3) If you are observing in a dark-sky location, you should be able to spot the gossamer band of the winter Milky Way stretching overhead from horizon to horizon. It's easiest to spot before the Moon rises or after it sets. The band's orientation across the sky and relative to the horizons will vary as the night progresses, but it will eventually move toward the western horizon, as the Earth spins toward the east and another morning. Slowly scan the length of the hazy band of light with your telescope to see thousands of otherwise invisible stars come within your reach. It is no less magic now than it was in the 17th century.

Crayon portrait of Galileo by Leoni

1 comment:

Denis Bauerschmidt said...

great post. it came up when my mom was looking to see if galileo had discovered that the milky way was made of many stars.

it was very interesting.