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.
At first glance, this cosmic kaleidoscope of purple, blue and pink offers a strikingly beautiful — and serene — snapshot of the cosmos. However, this multi-coloured haze actually marks the site of two colliding galaxy clusters, forming a single object known as MACS J0416.1-2403 (or MACS J0416 for short), 4.3 billion light-years away from Earth.
This scene captured by the NASA/ESA Hubble Space Telescope shows PGC 83677, a lenticular galaxy — a galaxy type that sits between the more familiar elliptical and spiral varieties in the Hubble sequence. Studies have uncovered signs of a monstrous black hole in the core of PGC 83677 that is spewing out high-energy X-rays and ultraviolet light.
In this NASA/ESA Hubble Space Telescope image we see the striking face-on spiral galaxy NGC 6814, whose luminous nucleus and spectacular sweeping arms are rippled with an intricate pattern of dark dust. The galaxy was discovered by William Herschel in 1788. NGC 6814 lies 74.4 million light-years away in the constellation of Aquila.