Iota Cancri: Hard to Say, Easy to See

April 24, 2009

While its name sounds like a disease you’d catch after a weekend of incautious living, iota Cancri (pronounced “eye-OH-tah KAN-kree”) is actually a pretty double star in the northern part of the constellation Cancer, the Crab.  This pair is easy to separate and striking in a small telescope, which makes it a pleasant diversion for those gazing at the nearby “Beehive” cluster.



The Basics

• The two components of Iota Cancri are a yellow giant star of magnitude 3.9 and a dimmer blue-white main sequence star of magnitude 6.8.  The contrast in color and brightness make the pair especially striking.

• With a telescope, low power and a slight defocusing will enhance the color contrast.

The double star iota Cancri, 7 degrees north of the Beehive Cluster

• The star is located in northern Cancer, just 7 degrees north of the Beehive Cluster.  The coordinates are RA 8h46m, Dec +28d45m.

• The brighter star has the same surface temperature as our sun, but it’s 200 time brighter and has evolved off the main sequence.   The fainter star is twice the mass of the sun, and revolves about its heavier companion every 60,000 years or so.

A Deeper View

• The stars are far apart from each other, some 2800 times the distance from the Earth to the Sun.  A planet near the brighter star would see the fainter star shining as bright as the full Moon does in our sky.  A planet near the fainter star would see the brighter star as 10 times as bright as the full Moon.

• With such a large separation, the stars may get ripped away from each other by chance gravitational encounters with passing stars.

• Two years ago, the tiny asteroid 411 Xanthe passed in front of iota Cancri.  You can see a video of the occultation here…

Good to Know

Just below iota Cancri lie gamma Cancri and delta Cancri, also called Aselus Borealis and Aselus Australis (the northern and southern donkeys), which according to legend, feed at the “heavenly manger” (the star cluster M44).  Both “donkeys” are double stars.

Personal View

While there are a few fine sights to see in this part of the sky, the star lore is even more interesting.  According to legend, the Crab was sent into the sky by the goddess Juno to bite Hercules as he battled the multi-headed water serpent Hydra.  Hercules crushed the Crab with his foot, yet the constellation remains prominent on the ecliptic thousands of years later.

** Highly Recommended **

Now anyone can quickly identify celestial objects with the SkyScout Personal Planetarium.  Just sight your object through the viewfinder and press the “Target” button.  SkyScout identifies the object on the LCD screen and plays an detailed audio description.  Click here to learn more…

Posted in Celestial Objects