Planetarium

Archive for December, 2008

Wednesday, December 10th, 2008

The full Moon of Dec. 12th is the biggest and brightest full Moon of the year.

It’s no illusion. Some full Moons are genuinely larger than others and this Friday’s is a whopper. Why? The Moon’s orbit is an ellipse with one side 50,000 km closer to Earth than the other. In the language of astronomy, the two extremes are called “apogee” (far away) and “perigee” (nearby). On Dec. 12th, the Moon becomes full a scant 4 hours after reaching perigee, making it 14% bigger and 30% brighter than lesser full Moons we’ve seen earlier in 2008. Above: In 2004, Greek amateur astronomer Anthony Ayiomamitis photographed an apogee Moon and a perigee Moon, and set the images side by side to show the difference. Okay, the Moon is 14% bigger, but can you actually tell the difference? It’s tricky. There are no rulers floating in the sky to measure lunar diameters. Hanging high overhead with no reference points to provide a sense of scale, one full Moon looks much like any other. The best time to look is when the Moon is near the horizon. That is when illusion mixes with reality to produce a truly stunning view. For reasons not fully understood by astronomers or psychologists, low-hanging Moons look unnaturally large when they beam through trees, buildings and other foreground objects. On Friday, why not let the “Moon illusion” amplify a full Moon that’s extra-big to begin with? The swollen orb rising in the east at sunset may seem so nearby, you can almost reach out and touch it.What you will see is the world around you. This is both the brightest and (in the northern hemisphere) the highest-riding full Moon of the year. If you go outside around midnight it will be close to overhead and act like a cosmic flood lamp making the landscape absolutely brilliant, especially if there’s snow. Full moons are always high during winter and, indeed, the solstice is right around the corner on Dec. 21st.  By: Dr. Tony Phillips, Science@NASA

 

Wednesday, December 10th, 2008

There is a giant black hole at the centre of our galaxy

 

German astronomers tracked the movement of 28 stars circling the centre of the Milky Way, using two telescopes in Chile. The black hole is four million times more massive than our Sun, according to the paper in The Astrophysical Journal. Black holes are objects whose gravity is so great that nothing – including light – can escape them. According to Dr Robert Massey, of the Royal Astronomical Society (RAS), the results suggest that galaxies form around giant black holes in the way that a pearl forms around grit. ‘The black pearl’ Dr Massey said: “Although we think of black holes as somehow threatening, in the sense that if you get too close to one you are in trouble, they may have had a role in helping galaxies to form – not just our own, but all galaxies. “They had a role in bringing matter together and if you had a high enough density of matter then you have the conditions in which stars could form. “Thus the first generation of stars and galaxies could have come into existence”. The researchers from the Max Planck Institute for Extraterrestrial Physics in Germany said the black hole was 27,000 light years, or 158 thousand, million, million miles from the Earth. “Undoubtedly the most spectacular aspect of our 16-year study, is that it has delivered what is now considered to be the best empirical evidence that super-massive black holes do really exist,” said Professor Reinhard Genzel, head of the research team. “The stellar orbits in the galactic centre show that the central mass concentration of four million solar masses must be a black hole, beyond any reasonable doubt.” Observations were made using the 3.5m New Technology Telescope and the 8.2m Very Large Telescope (VLT) in Chile. Both are operated by the European Southern Observatory (Eso). By Pallab Ghosh Science correspondent, BBC News