05-04-2008 Galileo’s Footsteps (Article 131)

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Simon Kenny
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Location: Shannon, Co. Clare, Ireland

05-04-2008 Galileo’s Footsteps (Article 131)

Post by Simon Kenny » Fri Jan 02, 2009 4:28 pm

Galileo’s Footsteps (Article 131)

This year sees the 400th anniversary of the invention of the telescope, and while most people have never heard of the Dutch inventor, Hans Lippersey, they have heard of the first person to use it, a year afterwards, for astronomical purposes. At the beginning of the 17th century, the Italian Galileo opened our eyes to the hidden wonders of the Universe which until then was subject to our fears, myths and theoretical scientific understanding.
One of the objects he viewed in 1610 is visible to the unaided eye in the constellation of Cancer, the Crab. This was the open cluster of stars, whose catalogue number, assigned over a century later, is M44. Known since antiquity as Praesepe, or the beehive, M44 belongs to the faintest of the zodical constellations, and was one of the objects in deep space viewed by Galileo, the first astronomer we know to have an instrument. While on a dark night it appears as a misty blur of light to the unaided eye, it is a magnificent object in binoculars, yet looks relatively poorly endowed through a small reflecting telescope. It is one of the many objects that appear better in binoculars than a telescope due to its large apparent size. M44 is visible during March high in the south near the zenith, and to the west (right) of Leo.

When Galileo viewed M44 with his, and by today’s standards, very poor quality optics, his tiny 30mm diameter telescope allowed him to count 40 stars within the central region of the cluster. Today, his experiment can be repeated easily by an amateur who may wish to walk in Galileo's footsteps. A 60mm refracting telescope is the typical smallest size available on the market today, yet viewing M44 from urban skies in a 60mm you will be very lucky to count more than 30, and even that is tops! The 60mm 'scope captures 4 times the amount of light that a 30mm 'scope does, yet why do we see less stars in the same object? The answer perfectly illustrates the effects due to urban light pollution from our cities and towns.

That said, if you get a chance to view it from a dark rural site in the same instrument, the view will be breathtaking, including colour in the brighter members. Galileo would be pleased. Maybe that is his footsteps you hear each night when you ponder the wonders of the night sky. However, take comfort from the great man, whose fortuitous use of a spectacle maker's invention to feed his curiosity, still gives memorable moments to so many astronomers almost 400 years later. Today, we know M44 lies 525 light years away and contains over 350 stars. It lies within 1 degree of the path of the ecliptic thus often provides fine conjunctions with solar system objects such as the Moon, planets and asteroids. Clear skies.

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