Showing posts with label moons. Show all posts
Showing posts with label moons. Show all posts

January 13 - Galileo Discovers Callisto

    Posted on January 13, 2022


This is an update of my post published on January 13, 2011:






News flash: January 13, 1610: 

Galileo Galilei discovered a fourth moon of Jupiter. 

But he did not choose the name “Callisto”!


To some extent people who discover new lands, comets, animals, elements, moons (and so on!) get the privilege of naming them—but at times those names are changed later. Galileo called this moon IV, the Roman numeral “4,” to distinguish it from Jupiter's other moons, I, II, and III. This turned out to be confusing, as many other planets turned out to have their own moons—quite a lot of moons, in some cases!—and we now know that Jupiter alone has 79 moons (at least! —stay tuned!).


The "Galilean moons" are Jupiter's largest four, the four Jovian
moons discovered by Galileo. 

The photo below shows roughly what Galileo would have seen
through his telescope.



A German astronomer who lived at the same time as Galileo, Simon Marius, claimed to have discovered Jupiter's moons before Galileo. Looking at the evidence, it seems possible that Marius discovered the Jovian moons independently of Galileo—but a few days later. Marius suggested naming Jupiter's moons for female mythological characters associated with Jupiter: Io, Europa, Ganymede, and Callisto. But because of the dispute over priority, Galileo never adopted those names—he stuck with his Roman numerals.




It seems that Marius's suggested names were officially adopted in the mid-1800s and became commonly used in the 1900s. At that point, Roman numerals were used for the smaller, newly-discovered V through XII, but in the 1970s the smaller Jovian moons were named after other lovers, favorites, and daughters of Jupiter. A few of the smaller moons are still waiting for a name, as far as I can tell.

Take a Peek at Jupiter's Moons

With a small telescope or a good pair of binoculars, you can spot Callisto and Jupiter's other largest moons. Check for the time when Jupiter will rise in an almanac such as the Time And Date online almanac.  

Here's a great video about why Callisto might be home to a human colony some day!




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August 28 - Discovery of a Very Special Moon!

 Posted on August 28, 2021


This is an update of my post published on. August 28, 2010:


When Sir William Herschel first spotted Saturn's moon Enceladus, on this date in 1789, he didn't know it was special. It just looked like a little speck of light circling the magnificently ringed planet.

But we now know better. We had a spacecraft way out there near Saturn, Cassini, for almost two decades. It circled Saturn, taking measurements and photos, for 20 years. And what it showed about Enceladus is that half of the moon is cratered (like most planets and moons in the solar system) but the other half is smoooooth. Even more interesting, there are “tiger stripes,” which are four depressions or cracks, on one portion of the smooth half (shown here with false color), and water geysers periodically go off through cracks. The water instantly turns into ice, of course, and it is the apparently the snow made from these geysers that fills in and covers the craters and makes that part of the moon smooth.



That's pretty surprising, and nobody knows why the cracks and geysers are only on one part of the moon instead of scattered pretty evenly over the moon.

Recently, complex organic molecules - the ingredients for life! - were discovered coming up in those geysers. Hopefully we can get another spacecraft way out there to detect if there is life in the depths of the moon.



Enceladus is in the thickest part of the sparse "E ring."

It's only the sixth largest of Saturn's moons, only about 314
miles (or 505 km) in diameter. I read that it could fit inside
the borders of Arizona!






Also on this date:
















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December 18 - Space! The Last Frontier!

Posted on December 18, 2019

Of course there's plenty of stuff to explore here on planet Earth - we will hopefully make more discoveries about the ocean floor, the deepest trenches, and the interior of the Earth, for example, and of course there's still TONS to learn about the complexities of living things and especially brains.

But as far as new lands to visit, explore, and maybe even settle - that we'll only find in space.


Today is the anniversary of several space-related events:

On this date in 1958, the world's first communications satellite was launched.

Called Project SCORE (Signal Communications by Orbiting Relay Equipment), it was the world's first purpose-built communications satellite, the second test of a communications relay system in space, and the first broadcast of a human voice from space. U.S. President Dwight D. Eisenhower did NOT go up in the Atlas rocket, of course (at this point in history, there had been no humans in space), but there was an on-board tape recorder that played a tape with Eisenhower's Christmas message to the world!

On this date in 1966, astronomer Richard Walker discovered another of Saturn's moons.

Back in the olden days, all our discoveries about space began from observations made on Earth. Since then we have invented space telescopes and manned and unmanned explorers that fly by or orbit or land on a moon or planet or what-have-you.  

In 1966, some of this unmanned fly-by and lander stuff had already happened, but most discoveries were still done with a telescope and photographic plates and painstaking comparison of photographs. That kind of careful comparison is how Walker discovered what is sometimes called Saturn XI - the eleventh moon of Saturn's to be discovered. ("XI" is the Roman numeral for "11.") This moon has been named Epimetheus.

Saturn's moon Epimetheus (above) is named for
one of the Titans in Greek mythology (below),
even though the resemblance is not all that striking!

On this date in 1973, the Soviet Union launched Soyuz 13.

This manned spaceflight was the Soviet Union's first mission dedicated to science. The Soyuz was especially changed in order to carry the Orion 2 Space Observatory, which collected information about stars' ultraviolet spectra.

On this date in 1999, NASA launched the Terra platform with five Earth-sensing instruments.

This launch was performed by the U.S., but the Terra platform represented scientists from around the world. The platform name was the result of a contest among high school students; Terra means "Earth" in Latin. The various instruments on Terra included infrared sensors that create high resolution images of ice, clouds, and land surfaces; instruments that took spectral readings; and instruments that measured and tracked pollution. Data collected from Terra help scientists understand climate change, the way pollution spreads, and trends in aerosol and carbon monoxide pollution.

On this date in 2018, a meteor exploded over the Bering Sea. 
The explosion was 10 times greater than the atomic bomb that destroyed Hiroshima. Luckily, this meteor exploded 16 miles above a sea rather than right on a city! - and so nobody even noticed...
We were just talking about the instruments on the Terra platform (see above), and it turns out that the only reason we know about this 2018 explosion is because one of Terra's instruments captured an image of the meteor's remnant and its dark trail of smoke just a few minutes after the explosion. The white background is the surface of the clouds above the sea.
The brown diagonal streak near the center
of the photo is the meteor fragment
that was caught on camera.



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