Using basic trigonometry, astronomers can directly calculate the distances to nearby stars by measuring the tiny shift in position that occurs as Earth sweeps from one side of its orbit to the other. But what about globular clusters, the huge star swarms that orbit the core of the Milky Way? They are typically too far away to measure the tiny angles needed to make the calculations. Instead, astronomers were long forced to estimate distances based on stellar evolution theory and how the brightness and colours of stars in a globular cluster differed from similar nearby suns. But last year, the Hubble Space Telescope managed to directly measure the distance to NGC 6397, one of the nearest globulars to Earth, to an accuracy of just 3 percent. The answer? 7,800 light years. The cluster apparently formed some 13.4 billion years ago, shortly after the big bang.
This Hubble Space Telescope image shows globular cluster NGC 1783 in the Southern Hemisphere constellation of Dorado. NGC 1783 lies within the Large Magellanic Cloud, a satellite galaxy of our Milky Way, some 160,000 light-years from Earth. NGC 1783 is thought to be less than 1.5 billion years old — very young for a globular cluster.
This NASA/ESA Hubble Space Telescope image reveals NGC 1222, a galaxy with a rather eventful story to tell. NGC 1222 has been described as a peculiar example of a so-called lenticular galaxy, but one that exhibits very recent star formation on a huge scale — an event known as a starburst — due to having recently consumed two dwarf galaxies.