M4 is one of the easiest globular clusters to locate. If you have a pair of binoculars, and your southern horizon is clear just after sunset, you can find the constellation of Scorpio and its brightest star, Antares. Tucked deep in the claw of the scorpion is M4, a globular star cluster only 43 quadrillion miles away.
Does that seem like a long way away? If NASA had been able to aim Voyager 1 in the direction of M4, it would take more than 4.7 billion years to reach the target. That’s longer than the current age of the Earth and Sun.
Needless to say, conventional travel will never get us to M4, let alone any other globular cluster orbiting our galaxy. We can only imagine, so check out this animation.
Philippe Loys de Chéseaux discovered this body in 1745 and a generation later Charles Messier catalogued it as his number 4. It took another generation for telescopes to discern individual stars.
M4 is as large as the moon as seen from Earth, but it is significantly smaller than numbers 3 and 2 on the Messier list. Every 120 million years M4’s orbit takes it deep into the center of our galaxy. Astronomers suppose that its outer stars have been stripped away over the eons. As a result, M4 has only about one-fifth the number of stars as M3.
Image credit: By ESO Imaging Survey – https://www.eso.org/public/usa/images/eso1235a/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=94663247