Cancer

Cancer is a faint constellation and its brightest star reaches only 3.5m. It is the only constellation in which there is a deep-sky object that is brighter than the brightest stars of the constellation – M 44 shines at 3.1m. As part of the zodiac, Cancer is one of the oldest constellations.

ι Cancri can be separated as a beautiful double star even at 7x magnification. A 4.0m bright yellow giant is orbited by a 6.6m bright bluish companion. A telescope with at least 300x magnification will show that a total of five stars belong to the system – ι¹ is a double star, ι² even a triple star. However, ι is only an optical double star. The brighter ι¹ is about 300 light-years away, while only 188 light-years separate us from ι². But the uncertainty in the distance measurement for ι² is at least 85 light-years.

M 44 is also well known as the Beehive-Cluster or Praesepe. The amount of proper names already shows that this is a popular object. The 1.5° large star cluster has been known since ancient times, where it was known as a weather sign – If the „little cloud“ in Cancer remained invisible in spite of a clear sky, a storm was coming. It was not until 1610 after the invention of the telescope that Galileo could see more than a small cloud. Today, even binoculars show up to 75 of about 200 stars easily. They form a 15 light-years wide open star cluster at 525 light-years distance. With 3.1m its overall brightness is higher than that of the brightest single star in Cancer.

The star cluster was formed 650 to 700 million years ago. It is one of the older star clusters and similar in age to the Hyades in Taurus. It also shares its speed and probably the place of origin, so that the two clusters may have a common origin. Praesepe and Hyades, as well as many stars between the two clusters, belong to the Hyades Stream, the remains of an old stellar association that has already circled the galaxy three times. Our much older Sun is currently in the middle between the stars Hyades Stream.

M 67 is a 30 arcmin large cluster with more than 500 stars. However, its brightest members reach only 10m, so most binoculars can only show a patch of light. It is much older than M 44, only NGC 188 in Cepheus could be even older. Its age is estimated at 3.9 billion years, some sources give an age of 10 billion years – about as old as some globular clusters. For comparison, our Sun has a life expectancy of about 11.5 billion years and was born 4.5 billion years ago. The 12 light-years large star cluster is located 1,500 light-years away from the galactic plane and is 2,500 light-years away from our Sun. M 67 is easy to find two 2° west of α Cancri.