(April schedule and May schedule)
Cancer constellation is winter-spring constellation and it is in best position for evening observing in March when it is high on the southern sky close to the zenith.
In February it is climbing on the southeastern sky, in March it is high on the southern sky and in best position for evening observing, in April it is high on the southwestern sky and in May it is low on the western sky.
We will observe it in April evenings when it is high on the southwestern sky and in May evenings when it is low on the western sky.
Double and multiple stars
Zeta Cancri - Its name is Tegmine. Its total visual magnitude on the sky is 4.7 and it is about 80 light years away from the Earth. It consists of two component stars Zeta1 Cancri and Zeta2 Cancri which need about 1,100 years to orbit once around their common center of mass (or common center of gravity).
The first component of this star system zeta1 is in fact binary star system composed of two stars which are separated on the sky by only 1 arc second, but their separation currently increases until 2018 or 2019. Their visual magnitudes are 5.3 and 6.3. Their orbital period is about 60 years. Their mass is a bit bigger than the mass of our Sun and they are main sequence stars with surface temperature about several hundred degrees K higher than that of our Sun. Catalogue designations for these two stars are HD 68257 and HD 68256.
The second component or zeta2 is separated on the sky from zeta1 about 6 arc seconds and its visual magnitude is 6.3. It is main sequence star similar to our Sun in mass, size and temperature. Interesting, zeta2 is also double star system because it is orbited by a companion separated by only about 0.3 arc seconds with visual magnitude 10. It is main sequence star and probably it is red dwarf star with orbital period of 17 years. The catalogue number for zeta2 is HD 68255.
Iota Cancri - It is not known yet if this star is a true binary star system or only visual double. The components are separated about 30 arc seconds on the sky.
The first component has visual magnitude 4.1 and is about 300 light years away. It is bright giant star, already expanded and with lower surface temperature than when it was main sequence star.
The second component has visual magnitude 6.6 and is a main sequence star more massive and hotter than our Sun. It is about 280 light years away from the Earth.
Deep sky objects
(can be observed only from dark location outside of the city)
M44 - It is an open cluster of stars. Its name is Praesepe and also the Beehive Cluster. Its visual magnitude is 3.7 and it is about 600 light years away from the Earth. It is visible with the naked eyes on the sky at night. Because it is so close to the Earth, it appears relatively large on the sky, with apparent diameter about 1.5 degrees. Its real diameter in the space is about 40 light years. Because of this, it is best to be viewed with binoculars, because if viewed with telescope will not fit completely in the field of view. Its age is about 600 millions years. Probably the cluster contains about 1,000 members, and because of its age, the stars are in all stages of evolution, like main sequence stars, red giants and also those which have finished their evolution and now are white dwarfs. Four red giants and one yellow giant can be seen, and 11 white dwarfs have been discovered. Also about 70 percent of the cluster members are red dwarfs and about 30% are Sun-like stars.
M 67 - It is an open cluster of stars. Its visual magnitude is 6.1 and it is about 2,500 light years away from the Earth. Its diameter in the space is about 20 light years. It is about 4 billion years old. It is very old for open cluster and among the oldest known open clusters of stars. It is known that once formed from a nebula, the open clusters do not last forever and in a period of several hundred million years they slowly lose their members and disappear - due to interaction with the interstellar material, interaction when passing through the spiral arms of the galaxy, passing close to other clusters of stars, interaction with other massive stars which throw cluster members out of the cluster, interaction of the cluster members between each other, explosion of one member in the binary star system in the cluster will throw the other member out of the cluster, also our galactic nucleus with its tidal gravitational forces strips the members of the cluster, and because of many other reasons. Probably when was born the cluster was ten times more massive. Because of its old age and its closeness, M 67 is intensively studied by astronomers, because it contains stars from all stages of their evolution. The study helps the fact that all members are the same age and distance, thus astronomers can also compare the stars and draw a lot of important conclusions about the stellar evolution. M 67 contains a lot of red giants, about 100 Sun-like stars, and about 150 white dwarfs. Even we amateur astronomers can make some conclusions, and that is: Because of its age, it does not contain hot blue and blue-white massive stars, because they finished like supernovae or white dwarfs several million years after the cluster was born.
Another old open cluster is NGC 188 in Cepheus constellation, and we will observe it too.