I received official warning today from Cardinal Bellarmine that I am not to teach or defend the Copernican Theory whereby the Earth moves around the Sun.
--Galilei
26 Feb 1616
Thursday, February 26, 2009
Thursday, February 19, 2009
Yay! No Moon!
This is a great weekend for observing as the light of the moon won't be washing out all the deep sky objects.
Starting in the solar system, though, we can observe Venus in the southwest after sunset. It's the brighter-than-any-star star-like object. Just about any telescope will show you what phase Venus is in.
Around midnight Saturn is high in the sky. It's hanging around the back legs of Leo right now. It's a fairly bright star-like object, a little cream-colored. Just about any telescope will show you the rings around Saturn. But this year the rings are nearly edge-on, so look for a thin line or ring around the planet.
A little later than Saturn, this year's bright comet (so far), Comet Lulin, is still brightening. From a dark location, I've read, you can see the comet with the unaided-eye. Lulin will be brightest the night of 23-24. Will it be bright enough to see with the unaided-eye from Parkville?
This is the time of year for observing open clusters. On Taurus' back is the Seven Sisters, or the Plieades. To the unaided-eye it looks like a very tiny Little Dipper. In even the smallest of 'scopes it looks like a swarm of stars.
North of Orion in the constellations of Gemini and Auriga are four of my favorite star clusters, all of them Messier objects (so they're fairly bright). M35 in Gemini is a star cluster I call the Soccer Ball because it sits at the feet of Castor, one of the twins of Gemini. Three clusters lie right in a row northwest of M35. These are M36, 37, 38 all in southeastern Auriga. A small to modest-sized 'scope will bring all of these into view.
Clear skies and enjoy.
Starting in the solar system, though, we can observe Venus in the southwest after sunset. It's the brighter-than-any-star star-like object. Just about any telescope will show you what phase Venus is in.
Around midnight Saturn is high in the sky. It's hanging around the back legs of Leo right now. It's a fairly bright star-like object, a little cream-colored. Just about any telescope will show you the rings around Saturn. But this year the rings are nearly edge-on, so look for a thin line or ring around the planet.
A little later than Saturn, this year's bright comet (so far), Comet Lulin, is still brightening. From a dark location, I've read, you can see the comet with the unaided-eye. Lulin will be brightest the night of 23-24. Will it be bright enough to see with the unaided-eye from Parkville?
This is the time of year for observing open clusters. On Taurus' back is the Seven Sisters, or the Plieades. To the unaided-eye it looks like a very tiny Little Dipper. In even the smallest of 'scopes it looks like a swarm of stars.
North of Orion in the constellations of Gemini and Auriga are four of my favorite star clusters, all of them Messier objects (so they're fairly bright). M35 in Gemini is a star cluster I call the Soccer Ball because it sits at the feet of Castor, one of the twins of Gemini. Three clusters lie right in a row northwest of M35. These are M36, 37, 38 all in southeastern Auriga. A small to modest-sized 'scope will bring all of these into view.
Clear skies and enjoy.
Our Telescope
About 10 months ago a rumor came to our ears that a spyglass had been made by a certain Dutchman by means of which visible objects, although far removed from the eye of the observer, were distinctly perceived as though nearby. About this truly wonderful effect some accounts were spread abroad, to which some gave credence while others denied them. The rumor was confirmed to me a few days later by a letter from Paris from the noble Frenchman Jacques Badovere. This finally caused me to apply myself totally to investigating the principles and figuring out the means by which I might arrive at the invention of a similar instrument, which I achieved shortly afterward on the basis of the science of refraction. And first I prepared a lead tube in whose ends I fitted two glasses, both plane on one side while the other side of one was spherically convex and of the other concave. Then, applying my eye to the concave glass, I saw objects satisfactorily large and close. Indeed, they appeared three thimes closer and nine times larger than when observed with natural vision only. Afterward I made another more perfect one for myself that showed objects more than sixty times larger. Finally, sparing no labor or expense, I progressed so far that I constructed for myself an instrument so excellent that things seen through it appear about a thousand times larger and more than thirty times closer than when observed with the natural faculty only. It would be entirely superfluous to enumerate how many and how great the advantages of this instrument are on land and at sea. But having dismissed earthly things, I applied myself to explorations of the heavens. And first I looked at the Moon from so close that it was scarcely two terrestrial diameters distant. Next, with incredible delight I frequently observed the stars, fixed as well as wandering, and as I saw their huge number I began to think of, and at last discovered, a method whereby I could measure the distances between them. In this matter, it behooves all those who wish to make such observations to be forewarned. For it is neccessary first that they prepare a most accurate glass that shows objects brightly, distincly, and not veiled by any obscurity, and second that it multiply them at least four hundred times and show them twenty times closer. For if it is not an instrument such as that, one will try in vain to see all the things observed in the heavens by us and enumerated in further "blogs." Indeed, in order that anyone may, with little trouble, make himself more certain about the magnificatoin of the instrument, let him draw two circles or two squares on paper, one of which is four hundred times larger than the other, which will be the case when the larger diameter is twenty times the length of the other diameter. He will then observe from afar both sheets fixed to the same wall, the smaller one with one eye applied to the glass and the larger one with the other, naked eye. This can easily be done with both eyes open at the same time. Both figures will then appear of the same size if the instrument multiplies objects according to the desired proportion. Now let us review the observations made by us during the past 2 months, inviting all lovers of true philosophy to the start of truly great contemplation....
-- Galilei
(Translated by Albert Van Helden, University of Chicago Press, 1989)
-- Galilei
(Translated by Albert Van Helden, University of Chicago Press, 1989)
Thursday, February 5, 2009
What's Up This Weekend?
An Astronomical Challenge
How many astronomical objects are visible in the daytime sky? There's the sun of course. And the moon, sometimes. Can you think of anything else?
How about Venus? In the night sky, at certain times of the year, only the moon outshines Venus. But does that mean Venus is bright enough to see in broad daylight? Many people are surprised to find out that the answer is yes.
It's difficult to see in the daytime sky and it takes practice or luck to do it, but I'm going to try to help you with a trick that I've been using recently to find Venus -- even at two in the afternoon. Right now, Venus is about 44 degrees from the sun. This is a little more than the width of two hand spans at arm's length. Actually, it's about 18-1/2 inches from the sun as measured by a yardstick held at arm's length.
Now using the sun to find things in the daytime sky can be bad for your eyes, so use the corner of a building or something to block the sun. Hold the yardstick up to the object blocking out the sun. Venus will be at about a 10 o'clock position relative to the sun. Venus will be a pale point of light in the sky, so it will be difficult to see at first. If after searching around about 18-1/2 inches from the sun you don't see Venus you may want to hunt in that area of the sky with binoculars. Do NOT point the binoculars in the direction of the sun. If you are a child, get your parents help.
Happy hunting! If you still can't find Venus, feel free to stop by the store some clear afternoon Tuesdays - Saturdays and I'll help you out.
How many astronomical objects are visible in the daytime sky? There's the sun of course. And the moon, sometimes. Can you think of anything else?
How about Venus? In the night sky, at certain times of the year, only the moon outshines Venus. But does that mean Venus is bright enough to see in broad daylight? Many people are surprised to find out that the answer is yes.
It's difficult to see in the daytime sky and it takes practice or luck to do it, but I'm going to try to help you with a trick that I've been using recently to find Venus -- even at two in the afternoon. Right now, Venus is about 44 degrees from the sun. This is a little more than the width of two hand spans at arm's length. Actually, it's about 18-1/2 inches from the sun as measured by a yardstick held at arm's length.
Now using the sun to find things in the daytime sky can be bad for your eyes, so use the corner of a building or something to block the sun. Hold the yardstick up to the object blocking out the sun. Venus will be at about a 10 o'clock position relative to the sun. Venus will be a pale point of light in the sky, so it will be difficult to see at first. If after searching around about 18-1/2 inches from the sun you don't see Venus you may want to hunt in that area of the sky with binoculars. Do NOT point the binoculars in the direction of the sun. If you are a child, get your parents help.
Happy hunting! If you still can't find Venus, feel free to stop by the store some clear afternoon Tuesdays - Saturdays and I'll help you out.
Tuesday, February 3, 2009
Astronomical Message
In this series of "blogs" I propose great things for inspection and contemplation by every explorer of Nature. Great, I say, because of the excellence of the things themselves, because of their newness, unheard of through the ages, and also because of the instrument with the benefit of which they make themselves manifest to our sight.
Certainly it is a great thing to add to the countless multitude of fixed stars visible hitherto by natural means and expose to our eyes innumerable others never seen before, which exceed tenfold the number of old and known ones.
It is most beautiful and pleasing to the eye to look upon the lunar body, distant from us about sixty terrestrial diameters, from so near as if it were distant by only two of these measures, so that the diameter of the same Moon appears as if it were thirty times, the surface nine-hundred times, and the solid body about twenty-seven thousand times larger than when observed only with the naked eye. Anyone will then understand with the certainty of the senses that the Moon is by no means endowed with a smooth and polished surface, but is rough and uneven and, just as the face of the Earth itself, crowded everywhere with vast prominences, deep chasms, and convolutions.
Moreover, it seems of no small importance to have put an end to the debate about the Galaxy or Milky Way and to have made manifest its essence to the senses as well as the intellect; and it will be pleasing and most glorious to demonstrate clearly that the substance of those stars called nebulous up to now by all astronomers is very different from what has hitherto been thought.
But what greatly exceeds all admiration, and what especially impelled us to give notice to all astronomers and philosophers, is this, that we have discovered four wandering stars, known or observed by no one before us. These, like Venus and Mercury around the Sun, have their periods around a certain star notable among the number of known ones, and now precede, now follow, him, never digressing from him beyond certain limits. All these things were discovered and observed a few days ago by means of a glass contrived by me after I had been inspiered by divine grace.
Perhaps more excellent things will be discovered in time, either by me or by others, with the help of a similar instrument, the form and construction of which, and the occasion of whose invention, I shall first mention briefly, and then I shall review the history of the observations made by me.
(HMS Beagle note: Galileo translated by Albert Van Helden, Sidereus Nuncius or The Sidereal Messenger, University of Chicago Press, 1989)
Certainly it is a great thing to add to the countless multitude of fixed stars visible hitherto by natural means and expose to our eyes innumerable others never seen before, which exceed tenfold the number of old and known ones.
It is most beautiful and pleasing to the eye to look upon the lunar body, distant from us about sixty terrestrial diameters, from so near as if it were distant by only two of these measures, so that the diameter of the same Moon appears as if it were thirty times, the surface nine-hundred times, and the solid body about twenty-seven thousand times larger than when observed only with the naked eye. Anyone will then understand with the certainty of the senses that the Moon is by no means endowed with a smooth and polished surface, but is rough and uneven and, just as the face of the Earth itself, crowded everywhere with vast prominences, deep chasms, and convolutions.
Moreover, it seems of no small importance to have put an end to the debate about the Galaxy or Milky Way and to have made manifest its essence to the senses as well as the intellect; and it will be pleasing and most glorious to demonstrate clearly that the substance of those stars called nebulous up to now by all astronomers is very different from what has hitherto been thought.
But what greatly exceeds all admiration, and what especially impelled us to give notice to all astronomers and philosophers, is this, that we have discovered four wandering stars, known or observed by no one before us. These, like Venus and Mercury around the Sun, have their periods around a certain star notable among the number of known ones, and now precede, now follow, him, never digressing from him beyond certain limits. All these things were discovered and observed a few days ago by means of a glass contrived by me after I had been inspiered by divine grace.
Perhaps more excellent things will be discovered in time, either by me or by others, with the help of a similar instrument, the form and construction of which, and the occasion of whose invention, I shall first mention briefly, and then I shall review the history of the observations made by me.
(HMS Beagle note: Galileo translated by Albert Van Helden, Sidereus Nuncius or The Sidereal Messenger, University of Chicago Press, 1989)
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