Starship Asterisk*

http://gishbar.blogspot.com/ wrote:
<<In early January 1610, Galileo had just finished up an incredible series of observations of the Moon, the Milky Way, and several stellar nebulae. In the case of the Moon, his 20-power telescope revealed the Moon's cratered and mountainous surface, showing that it was not smooth and perfect as stated in the Aristotelian world view, but was in fact, quite rough. Galileo discovered a multitude of stars, far more than could be seen with the naked eye, within the "clouds" of the Milky Way, on the belt of the constellation Orion, and within nebulae and star clusters such as the Orion Nebula, Beehive Cluster, and the Pleiades. During the first week of January 1610, Galileo drafted a letter to Galileo's Florentine friend, Enea Piccolomini describing these observations along with details on how best to operate the telescope for astronomical viewing, for example, suggesting the use of a stand for the telescope to prevent inadvertent hand motions from ruining observations. Galileo set aside the letter for a few days, picking it back up on the evening of January 7, 1610.

That evening, an hour after sunset, Galileo aimed his 20x telescope, with a newly masked objective lens, toward the planet Jupiter, at the time near opposition and in the midst of its retrograde loop in the night sky. In this case he observed three stars forming a line with Jupiter, parallel to the ecliptic. Two of these stars were to the lower left (east) of Jupiter and another star was to the upper right (west) of the planet. He noted this in the conclusion of his letter to Piccolomini:

• ... and only this evening I have seen Jupiter accompanied by three fixed stars, totally invisible by their smallness, and the configuration was in this form nor did they occypy more than one degree of longitude. The planets are seen very rotund, like little full moons, and of a roundness bounded and without rays. But the fixed stars do not appear so...

On January 7, 1610, Galileo discovered what we call today the Galilean moons, believing them at the time to be fixed stars behind Jupiter. When I first read this passage, I assumed he was referring to the moons as "The planets" in that last section, hence my anniversary message earlier today. However, re-reading that and understanding the timing of when that was written, the very night he made his first observation of these satellites, he was actually referring to planets like Venus, Jupiter, or Mars as "little full moons", and that these "fixed stars" do not appear like that. This again drives home the point that on January 7, the day of discovery, Galileo hadn't figured out what he found, but it was enough for him to keep making observations over the following days.

A quick note: Galileo refers to having seen three little stars, not four. In fact, he did see all four Galilean satellites. Ganymede was the lone star to the west of Jupiter and Callisto the star furthest east. The eastern star closest to Jupiter was actually two moons, Io and Europa, too close together for Galileo's low-powered telescope to separate.>>

http://en.wikipedia.org/wiki/Galileo_Galilei wrote:

• Behold therefore, four stars reserved for your famous name, and those not belong to the common and less conspicuous multitude of fixed stars which, with different motions among themselves, together hold their paths and orbs with marvelous speed around the planet Jupiter, the most glorious of all the planets, as if they were his own children, while all the while with one accord they complete all together mighty revolutions every twelve years around the center of the universe, that is, round the Sun.
  - From Galileo's Sidereus Nuncius (trans. by Edward S. Carlos)

<<In 1610 Galileo published an account of his telescopic observations of the moons of Jupiter, using this observation to argue in favour of the sun-centered, Copernican theory of the universe against the dominant earth-centered Ptolemaic and Aristotelian theories. The next year Galileo visited Rome in order to demonstrate his telescope to the influential philosophers and mathematicians of the Jesuit Collegio Romano, and to let them see with their own eyes the reality of the four moons of Jupiter.
While in Rome he was also made a member of the Accademia dei Lincei.>>

http://www.planetary.org/blog/article/00002298/ wrote:
400 Years of the Galilean Satellites
By Emily Lakdawalla Jan. 7, 2010

<<It was 400 years ago today that Galileo discovered smaller planets attending the planet Jupiter. Jason Perry is doing a far better job than I could of writing about the momentous discovery on his blog, the Gish Bar Times. This post serves as an index to his thoroughly researched history, and he's also maintaining an index to other bloggers' writings on the topic here.

In addition to Jason, I also want to highlight the ongoing work of Paul Schenk, who will soon be publishing an Atlas of the Galilean Satellites. He's been studying outer planet moons -- more specifically, the topography of outer planet moons (and what that says about their geology) -- since the 1980s. While in Padua for an event celebrating the anniversary, he uploaded a bunch of spectacular 3D flyovers of the Galilean moons to his Youtube channel; numerous screen grabs from his movies can be viewed at his blog, Dr. Schenk's 3D House of Satellites. My favorites include this one, showing a nine-kilometer-high mountain peak next to a caldera on Io:
http://www.youtube.com/watch?v=q3Yji2ck ... r_embedded

...and this one, showing the rumpled, peaky terrain of Callisto's plains.
http://www.youtube.com/watch?v=LILgPtbQ ... r_embedded

Both are vertically exaggerated, the Callisto one much more than the Io one.

Agenor Linea, Europa

Stretching 1400 kilometers across Europa, Agenor Linea is a mysterious feature composed of numerous parallel ridges. In this view, made from Galileo data, we see a part of Agenor that is 20 kilometers wide, with a few hundred meters of relief from ridge top to trough bottom (there is some vertical exaggeration). Adjacent to Agenor are regions of chaos. Mapping suggests that some strike-slip motion has occurred across the feature. Credit: Paul Schenk>>

Astronomy. What's the first thing you think of when you read that word? The many beautiful vistas returned from Hubble? A family in a backyard huddled around a small telescope? Giant research observatories such as the Keck? Whatever may come to mind, it usually involves a telescope. But the very nature of telescopes has changed over the centuries, with different arrangements of lenses dominating for decades before succumbing to some combination of basic physics or technical limitations. We'll (somewhat belatedly) celebrate the 400th anniversary of Galileo's telescope by taking you on a quick tour of four centuries of progress and frustration.