Posts tagged moon
Posts tagged moon
by Neil deGrasse Tyson
From Natural History Magazine
Science consists in discovering the frame and operations of Nature, and reducing them, as far as may be, to general rules or laws—establishing these rules by observations and experiments, and thence deducing the causes and effects of things.
In scientific inquiry, often the answer to one simple question fortuitously explains the answers to many others; they may even answer questions that have yet to be conceived. Powerful ideas unify concepts or phenomena that were previously thought to be unrelated. For example, Sir Isaac Newton identified a falling apple and Earth’s orbiting moon as different effects of a single law of universal gravitation represented by a simple equation. (The falling apple did not actually hit Sir Isaac on the head. He saw it fall from afar.)
Newton’s famous equation is a recipe to compute the force of gravity between any two objects in the universe. With a basic application of Newton’s equation you can show that the force of gravity is greatest where an object is nearest another object and least at the point where it is farthest. As you stand on Earth, for example, Earth’s gravity is slightly stronger at your feet than at your head. The differential is small, so don’t blame your light-headedness on this phenomenon. Earth pulls on your feet with a force that is only one ten thousandths of one percent stronger than that at your head.
This simple difference in gravity, officially known as the tidal force, is felt by all objects as they are pulled by the gravity of all other objects in the universe. Tidal forces are the direct cause of a diverse array of cosmic phenomena that otherwise seem to have nothing to do with one another. Some of my favorites: the daily rise and fall of Earth’s oceanic tides; Earth’s gradually slowing rotation rate, which is making the days longer and longer; the Moon’s slow spiral away from Earth; the Moon showing only one face toward Earth at all times; Pluto, and its lone moon Charon, showing each other only one face during their mutual orbit; the geological (or is it iological?) activity of Io, one of Jupiter’s moons; the breaking apart of comet Shoemaker Levy-9 in its close encounter with Jupiter; the long tails of colliding galaxies in collision; and the spectacularly gory death to which you would succumb if you approached the center of a black hole (as detailed in last month’s Universe essay Death by Black Hole).
Tidal forces are strongly dependent on distance. A mild increase in distance between two objects can make a large difference in the strength of the tidal force. For example, if the Moon were just twice its current distance from us, then its tidal force on Earth would decrease by a factor of eight. At its current average distance of 240,000 miles from Earth, the Moon manages to create sizable atmospheric, oceanic, and crustal tides by attracting the part of Earth nearest the Moon more strongly than the part of Earth that is farthest. (The Sun is so far away that in spite of its generally strong gravity, its tidal force on Earth amounts to less than half that of the Moon.) The oceans respond most visibly in being stretched toward the direction of the Moon. Meanwhile, as the solid Earth continues to rotate, the continental shelves are constantly trying to push forward the1.5 quintillion tons of bulging ocean water.
The Earth’s moon 1.5 days after its New Moon phase, with the International Space Station seen streaking across the sky and Jupiter shining amid the clouds.
Worth reblogging. Just beautiful.
Never have I felt such contentment before. I am so full of emotion but I am speechless. Words cannot begin to express the feelings that have been elicited by the wonders that I have experienced tonight.
The Moon. She is the most beautiful thing to me; it truly is one of my favourite things. It is such a humbling experience to see the Moon with merely the naked eye; but what I have seen tonight… nothing can ever compare. Never have I seen such beauty in my life. The surfaces, the textures, the shades; the craters, the hills lit along the shadow. The most beautiful thing has been completely exposed for it’s raw existence and the feelings that followed will hardly be matched by any other.
Then Saturn. A little speck of light in our night sky, but with the use of such an amateur tool, it becomes it’s own world and it too, exposed for it’s true beauty. The rings, oh the rings. I thought it was too good to be true, but upon focusing the lens, the apparent ears became visible and there it was. This massive gas giant of a planet with beautiful rings visible by me. It looks just like it does in pictures. It is so hard to convince myself at this point that what I’m looking at is real. We have current understanding of Saturn’s rings, and even I am utterly dumbfounded upon their exposure; I cannot imagine what Galileo thought when he saw these “ears”…..
Lastly, Mars. There’s nothing too interesting visibly about Mars, I’ll have to admit. Although, it was a beautiful shade of red which can be seen by the naked eye. It is truly remarkable that these points of light are other worlds among Earth. I cannot wrap my mind around it. Massive bodies so far out in space that they appear as points of light to us here on our blue dot. Interestingly, they seemed to wander quite fast across the field of view and every few seconds, the telescope had to be readjusted. It really makes you appreciate the rate at which the Earth rotates which cannot by any means be appreciated unless you’re exposed to it directly. The parallax seen in a telescope, as seemingly mundane as it is, is quite remarkable.
Now, if only I could see Jupiter…
Two new satellites are now in orbit around the moon, and they could reveal whether our moon ate a sibling many moons ago.
They are designed to produce the most detailed map ever made of the lunar gravitational field, which is lumpy thanks to mountains, craters, lava flows, and larger irregularities – the moon’s far side is much more mountainous than its near side, for example.
"We don’t actually know why the near side and far side are different," says mission principal scientist Maria Zuber of the Massachusetts Institute of Technology in Cambridge.
One theory is that Earth once had two moons, and the second one wrapped itself around the lunar far side in a low-velocity collision that created the highlands. GRAIL will look for signs of such a crash.
It’s the ultimate buddy movie. Forty years ago, on November 19, 1969, astronauts Pete Conrad and Alan Bean landed on the moon in one of the most important of the Apollo flights. This video shows them making a pinpoint landing on a treacherous lunar surface, finding rocks, and generally having a blast. The program features an interview with Pete Conrad, filmed a year before he died in a tragic motorcycle accident in 1999. Credit Space.com with editorial assistance.
The MPG/ESO 2.2-metre telescope at La Silla in Chile is a powerful instrument that can capture distant celestial objects, but it has been used here to image a heavenly body that is much closer to home: the Moon. The data used for this image were selected by Andy Strappazzon from Belgium, who participated in ESO’s Hidden Treasures 2010 astrophotography competition. Andy’s composition of the Moon was the fourth highest ranked entry in the competition.
This image of the crescent Moon shows sunlight skimming across the heavily pocked surface, filling its craters with shadows. This is a fairly flat region of the Moon, but elsewhere, high mountains can be found, with some peaks reaching about 5000 metres. When backlit by the Sun, these mountains cast long shadows on the lunar surface. In the 1600s, Galileo Galilei used these long shadows to determine the height of the peaks.
At the Moon’s poles (not seen in this picture), some craters are permanently shadowed and the floors of some may have not seen sunlight for billions of years. Scientists had long suspected that these dark and constantly cold regions of the Moon could harbour water ice, but it wasn’t until late 2009 that evidence for this was found.
In a NASA mission called LCROSS (Lunar Crater Observation and Sensing Satellite), a spent rocket booster was sent on a one-way collision course to the Moon’s south pole, while the remaining part of the spacecraft hunted for evidence of water in the ejected debris. The mission was a success and its findings confirmed the presence of water ice within these dark craters. The finding has important implications for the future of human exploration of the Moon and elsewhere in the Solar System.
On Cerro Paranal, the 2600-metre-high mountain in Chile’s Atacama Desert that is home to ESO’s Very Large Telescope, the atmospheric conditions are so exceptional that fleeting events such as the green flash of the setting Sun are seen relatively frequently. Now, however, ESO Photo Ambassador Gerhard Hüdepohl has captured an even rarer sight: a green flash from the Moon, instead of the Sun. The photographs are very probably the best ever taken of the Moon’s green flash.
Gerhard was surprised and delighted to catch the stunning green flash in this series of photographs of the setting full Moon crossing the horizon, taken on a clear early morning from the Paranal Residencia.
The Earth’s atmosphere bends, or refracts, light — rather like a giant prism. The effect is greater in the lower denser layers of the atmosphere, so rays of light from the Sun or Moon are curved slightly downwards. Shorter wavelengths of light are bent more than longer wavelengths, so that the green light from the Sun or Moon appears to be coming from a slightly higher position than the orange and red light, from the point of view of an observer. When the conditions are just right, with an additional mirage effect due to the temperature gradient in the atmosphere, the elusive green flash is briefly visible at the upper edge of the solar or lunar disc when it is close to the horizon.
Moonset from the ISS. On 16th April ‘03 Don Pettit, the ISS science officer, imaged the full moon as it set behind the Earth’s limb. In this montage the relative positions of the moon are computed from the image times and the ISS orbital period.
As the ISS spun, the moon’s light dipped ever deeper into the earth’s atmosphere before leaving again. The path length is double that the setting moon seen from earth’s surface and the distortion by differential atmospheric refraction is correspondingly greater.
At first the lower limb is distorted most as the atmospheric lens pushes the lower limb upwards to create an egg shape (close-up). Finally the whole moon becomes an impossibly flattened oval. In the final frame the moon’s lower edge is slightly clipped by the earth’s surface.
The lower part of the disk and then the entire moon is appreciably reddened by preferential atmospheric scattering of blue light out of the ray path.