Pictured above is Omega Centauri, a globular star cluster that orbits the Milky Way galaxy and that has millions of stars in a sphere 150 light years across (150 light years is a bit more than 34 times the distance of the Sun from the nearest star). On the left-hand side is an image taken by an amateur astronomer (source), and it’s quite typical of what you would have seen with professional telescopes many years ago. On the right-hand side is what you get if you use ESO’s “Wide Field Imager (WFI), mounted on the 2.2-metre diameter Max-Planck/ESO telescope, located at ESO’s La Silla observatory, high up in the arid mountains of the southern Atacama Desert in Chile.” (source; note that I created the little composite above by eye using Photoshop, aligning some of the bright stars; this required rotating one of the images) That’s not even such a big telescope actually.
The difference is quite striking, though, especially if you look at a couple close-ups:
The last image is aesthetically a bit more interesting, but it’s the center image that’s the killer: A look at the cluster’s center (crop done by eye). These days, you can actually resolve individual stars in the center of globular stars clusters! If you wan to see the cluster in all its glory download the 8040 x 7560 pixel - 72MB full-resolution image.