Tag: Galileo

Happy birthday, Neptune!

By Phil Plait | July 12, 2011 6:00 am

Today is special: it is now one full Neptunian year since this giant planet was discovered in 1846!

So today is Neptune’s birthday! Um. Well, kinda.

Yeah, as usual, stuff like this gets complicated. I realized this anniversary was coming up about a year ago, and contacted an old friend about it: Kelly Beatty, editor at Sky and Telescope magazine, who then contacted astronomers John Westfall and Roger Sinnott. We had some fun email exchanges about all this! I think I have a good grip on this now, so let me explain.

The short form

First, to celebrate a birthday, you need the birthdate. That’s the first complication. Neptune was discovered on September 23, 1846 by astronomer Johann Galle using star charts by Johann Encke, and they are generally given credit for it. However, that date of September 23 is a bit dicey! Galle and Encke report that they found Neptune on 9/23 at 12:00:15 "Berlin M.T.", according to Westfall. But they reckoned the day starting at noon! And since they’re using Berlin mean time, you have to account for the longitude of Berlin with respect to 0° longitude on Earth. According to Westfall, once you do all that, you get a discovery time of September 23 at 23:06:40.

Worse yet, there may be some imprecision in the exact time the astronomers reported the discovery, although Galle reported the time to a fraction of a second. Westfall reports that might be as much as 1.2 hours, preferring a discovery time of September 24, 1846 at 00:15 GMT.

Who’s right? Turns out, it doesn’t matter much, since we only need to know the time to within a few hours to get the right date for the birthday. Still, Westfall appears to have looked at this pretty hard, so you know what? Good enough. I’ll use his numbers.

A year by any other name would take as long

OK, so we have the birthdate. Now, how long is a Neptune year?

Yeah, well, that turns out not to be so easy to answer either! Read More

CATEGORIZED UNDER: Astronomy, Cool stuff, Top Post

The Galilean Revolution, 400 years later

By Phil Plait | January 7, 2010 10:00 am

Four hundred years ago tonight, a man from Pisa, Italy took a newly-made telescope with a magnifying power of 33X, pointed it at one of the brighter lights in the sky, and changed mankind forever.

The man, of course, was Galileo, and the light he observed on January 7, 1610 was Jupiter. He spotted "three fixed stars" that were invisible to the eye near the planet, and a fourth a few days later.

Here is how he drew this, 400 years ago:


He noted the stars moved around Jupiter as they followed it across the sky, and so was the first to figure out that other planets had moons like our own. It wasn’t an easy observation; his telescope was still small, the field of view narrow (so not all the moons were visible at the same time), and the moons faint next to Jupiter’s brilliant glare. But Galileo persisted, and figured it out. We call these four the Galilean moons in his honor: Io, Europa, Ganymede, and Callisto.

Here’s how we see them today:


The image above [click to embiggen] is from the New Horizons spacecraft as it shot past Jupiter in early 2007, showing all four moons. Each is scaled to show its true relative size to the others. It’s impossible not to wonder what Galileo would have thought, knowing that just shy of 400 years after he made his first observations, we would fling our robotic proxies out into the solar system and get close up views of the objects he discovered.

Think of it! For all of time before, Jupiter was just a light in the sky. And then, forever after that night forty decades ago, it was a world, surrounded by more worlds.

[See more pictures of Jupiter and its moons in a gallery over at 80 Beats.]

Galileo went on to observe craters on the Moon, spots on the Sun, and the phases of Venus. It was that last that may have been his crowning achievement, because the way Venus showed phases meant it could not possibly orbit the Earth, and that it must orbit the Sun. The geocentric theory had held sway for over a thousand years, but Galileo proved it was wrong almost overnight. Of course, the Church wasn’t thrilled with this, though I suspect they might have rolled with it if Galileo hadn’t been such an arrogant jerk and published a manuscript insulting the Pope, a man who used to be his friend and supporter.

If there is a lesson in there, I leave it to my readers to suss it out.

Now, all these years later, a lot of legends exist over the man. He didn’t invent the telescope, he wasn’t the first to point it at the sky, and he wasn’t even the first to publish his drawings. But he was a merciless self-promoter, and because of that we do remember him now (again, any lessons learned here are up to you). And it’s not entirely unfair to do so; he was a tireless observer, a wonderful artist, a great inventor (he may not have been the first to build a telescope, but he made his far better than its predecessors) and a brilliant scientist who, even if he hadn’t done so much for astronomy, would still be remembered today for his other work.

Tonight, just after sunset, Jupiter will be a glowing white beacon in the southwest. I have a Galileoscope, an inexpensive telescope created as part of the International Year of Astronomy 2009, an effort to get as many people on Earth to look up as possible. I think perhaps it would be fitting if I brave the subzero temperature outside, maybe for just a few minutes, and take a look at the mighty planet. Tonight’s display is better than Galileo himself had it: all four moons will be perfectly arrayed, two on each side of Jupiter’s face.

I’m not a very religious man, nor am I a very spiritual man. But I know there will still be a sense of connection, a sense of wonder that I will have tonight that I will share with a man long dead, but whose life and achievements still echo through time.

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

Hub of beauty

By Phil Plait | November 10, 2009 11:03 am

When Galileo first turned his telescope to the sky, almost exactly 400 years ago, he could not possibly have known what he was starting.

Today, four centuries later, we’ve come a long, long way. To celebrate the anniversary of Galileo’s telescopic revolution, NASA’s Great Observatories — Hubble, Spitzer, and Chandra — have released a jaw-dropping mosaic of the very heart of the Milky Way galaxy. Behold!


[Oh yes, you want to click to embiggen that-- what I show here is a very compressed version. Or you can go here for a massive copy. You can also get wallpaper versions here.]

This image is nothing less than a heroic effort of astronomical artistry. It’s a chunk of the sky 38 x 14 arcminutes across, or about half the size of the full Moon, and it’s aimed right into the core of our galaxy. See the bright spot just to the right of the center? Buried in there behind light years of dust and gas is the monster of the Milky Way, a black hole with four million times the mass of the Sun. But even that is dwarfed by the 400 billion solar mass heft of the entire galaxy.

hst_spitzer_chandra_mw2There is so much going on in this image it’s hard to know where to start. But first… the Hubble images are in the near-infrared, with a wavelength a little more than twice what the eye can see (1.87 microns for those playing at home). That’s represented in the image as yellow. Spitzer contributed observations in four infrared wavelengths (3.6, 4.5, 5.8, and 8.0 microns), and those are depicted in red. Chandra sees X-rays which are normally written as units of energy, but to remain consistent with the other two images, they were at wavelengths of 0.0005, 0.00025, and 0.00016 microns, and are shown in blue.

What does all this mean? Different objects emit light at different characteristic wavelengths. Warm dust, for example, emits strongly in the infrared. Stars and warm gas emit visible and near-infrared light. Violently heated gas, affected by huge magnetic fields or shocked by colossal collisions glows in X-rays. So this image is a polychromatic view of the crowded downtown region of a bustling city: our galaxy.

You might want to look at an annotated version of this image so you can get your bearings. It’s worth it!

The huge arches of gas on the left are actually the edges of gigantic molecular clouds (dense nebulae where stars are born), lit up by the torrential blast of light from a clutch of massive stars nearby. This clot of stars, called the Arches Cluster due to the arcs it excites, can be seen as a small spot glowing blue just to the left of center in the picture. Don’t be deceived by its diminutive appearance: the Arches cluster has thousands of superstars in it, each dwarfing our Sun, and each capable of sleeting out vast amounts of radiation that lights up the gas surrounding it. Were this cluster much closer than its 25,000+ light year distance, it would blaze in our sky like a beacon. Replace the Sun in our solar system with just one of those stars, and the Earth would be fried beyond the capability of any life to survive. You might as well try living in the flame of an arc-welder.


Below and just to the left of the Arches is a clumpier, more twisted arc of gas called the Sickle. That’s a giant cavity being carved out of dense gas by the Quintuplet cluster, the pinkish glow in its center. It’s another nursery of stars like the Arches cluster, which is also blasting out light and stellar winds which eat away at the gas enveloping it. The Pistol Star resides there, perhaps one of the most massive stars in the Milky Way.

And there’s more! The blue glow on the left is from an X-ray binary called 1E1743.1-2834, what is probably a massive star being orbited by either a neutron star or a black hole. Matter is being stripped from the star and piling up outside the collapsed companion, where it gets heated up to millions of degrees and emits X-rays.

Supernovae remnants dot the image, as do stars, filaments of gas, clouds of dust, and more. This picture is an astronomer’s dream, a map of everything someone might want to visit with a starship — as long as the shields are at full strength. This image is also a map of violence, turbulence, and unrest… a typical scene, so we think, of any normal spiral galaxy like ours. And our Galaxy’s center is considered quiet by astronomers! Some are far worse.

But this is home for us. It’s a place of unimaginable fury but also astonishing beauty… and we see it now as we do because we have dared to examine the world around us, to use tools we invent to peer closer, to magnify the tiny, to extend our eyes into realms we once didn’t even know existed. And every time we do — every single time — we find more questions, more puzzles, more things to examine.

And we find art. Galileo wasn’t the first to turn his telescope to the sky, nor was he the first to record what he saw. But he was the one who made everyone see what he did, and for that, all these years later, he is owed a debt of gratitude.

CATEGORIZED UNDER: Astronomy, NASA, Pretty pictures

Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


See More

Collapse bottom bar

Login to your Account

E-mail address:
Remember me
Forgot your password?
No problem. Click here to have it e-mailed to you.

Not Registered Yet?

Register now for FREE. Registration only takes a few minutes to complete. Register now »