Cancer, also known as “the dark sign”, is a medium sized constellation surrounded by Gemini to the West, Leo, Canis Minor and Hydra.
The Brightest star in Cancer is Beta Cancri which only has an apparent magnitude of 3.5. So it’s brightest star isn’t overly bright and neither are the rest of them hence the name “the dark sign”. Cancer is the Latin word for Crab and throughout history it has been depicted as several different creatures.
In ancient Babylonia, Cancer was both a Crab and a snapping turtle at different times. In much later texts, Cancer was even illustrated as a water beetle and a lobster.
As for the other stars in Cancer, some actually have planets! 55 Cancri has five confirmed planets captured in its orbit including a Super Earth-like planet. It is eight times the mass of the Earth and orbits within the star’s habitable zone. This means that this super Earth is roughly the same distance from 55 Cancri as we are from the Sun. Theoretically, it is at a distance to support liquid water on its surface.
Sadly, the star itself is 41 light years from us so the chances are we will never have the technology to communicate with this planet never mind visiting it. The probe Voyager 2 has taken over 40 years to achieve a distance of 1 light day away! So a probe would take at least half a million years to get there!
The Beehive Cluster is also located in Cancer. It is one of the objects Galileo first observed with his telescope and was even able to distinguish some individual stars within the cluster. It’s a very popular target for amateur astronomers and one I particularly love looking at!
My favourite object in Cancer is a Quasar that cant been seen with the naked eye! A quasar is a supermassive black hole with an orbiting accretion disk of gas. As the gas falls into the black hole, energy is released in the form of electromagnetic radiation. The quasar itself is 8.4 Billion light years from Earth and was used to attempt to calculate the velocity of gravity!
Another pair of supermassive black holes exists in Cancer, OJ287, and are among the largest known to modern science. These black holes are believed to orbit one another. As the larger mass hole merged into the smaller one, gravitational waves propagate throughout the universe at the speed of light as predicted by Einstein. Recently, gravitational waves were found by the LIGO observatory which won them the Nobel Prize in Physics in 2017.
Next stop my own star sign Leo!