Canis Major constellation is winter constellation and it is in best position for evening observing in February and March when it is on the southern sky.
In January it is rising and is low on the southeastern sky, and in February and March it is in best position for observing when it is on the southern sky.
We will observe it in April early in the evening when it is very low on the southwestern sky and try to catch it before it sets behind the horizon.
Double and multiple stars
Alpha Canis Majoris - Its name is Sirius. It is the brightest star on the sky. Its visual magnitude is -1.5 (minus 1.5). It is one of the closest stars to the Earth - it is only 8.7 light years away. That makes it among the most studied stars on the sky by professional astronomers (of course after our Sun).
The companion is very interesting type of object - it is so-called white dwarf. That is the latest stage of the evolution of a star with mass smaller than 10 solar masses. Because around 98 percent of the stars in our galaxy have mass less than 10 solar masses, all of them will finish their life as white dwarfs. After spending all fuel inside its core during the life, and passing through red giant stage of its evolution, the star outer shell will split from the core during some period of time, and form a beautiful planetary nebula. What will left is the dense core of the star composed of degenerate matter with very high temperature and very small size. The mass of an average white dwarf is a bit more than half mass of our Sun, but its diameter is less than the diameter of our Earth! The white dwarfs are very dense objects, made of highly compressed stellar core. After forming the white dwarf is very hot - its temperature is about 10 million K, and remains steady inside, while only the thin outer shell cools. The outer shell of the white dwarf will cool slowly down from 10 millions K and will be visible for a long period of time. The surface temperature of the known white dwarfs are from several hundred thousands to several thousands K. Cooling will extend over billions of years - at the beginning faster and after slowly. The planetary nebula will disperse in a relatively short period of time into space and will not be visible anymore.
White dwarfs can have maximum mass of 1.4 solar masses after which it cannot exist as white dwarf. The mass of the Sirius companion is one solar mass. Its visual magnitude is 8.6 and should be easy target with a telescope, but that is not the case because the bright Sirius with its glare makes detecting and observing the companion very difficult. The age of the Sirius white dwarf companion is about 100 million years. It is the closest white dwarf to the Earth. Last decades a lot of new white dwarfs has been discovered in our galaxy, for a total of about 10,000. Hundred years ago astronomers did not even know about white dwarfs.
Sirius is sometimes referred as Sirius A and its white dwarf companion as Sirius B. Its orbital period is 50 years. The separation between Sirius and the companion is currently about 7 arc seconds and it is widening until around 2020, when will be 11 arc seconds (when they will be about 4.5 billion km apart). Sirius is main sequence star with two solar masses and 1.7 solar diameters, 10,000 K surface temperature. The Sirius A/B system is about 250 million years old. The now white dwarf was once more massive than Sirius, thus spent its nuclear fuel faster, went through red giant phase and finished as white dwarf, while less massive Sirius is still on the main sequence. Sirius B surface temperature is about 25,000 K and its diameter is the same as the Earth diameter. Sirius A will have fuel to stay on the main sequence for the next 750 million years, when will pass through a red giant phase and will also become a white dwarf.
Our Sun will also finish its life as a white dwarf after living about 10 billion years as a main sequence star fusing hydrogen into helium. In these 10 billion years our Sun will spend all hydrogen in its core after fusing it into helium. In a short period of time after this, it will start fusing helium into carbon and oxygen in its core and leave the main sequence and go through the phase of a red giant. Will spend all its helium inside its core and will no longer be able to fuse other elements. That means the fusion inside its core will stop and will not be able to produce energy anymore. The core material will compress under its own gravitation and will become very dense. The outer shells will left the core forming planetary nebula. The very hot, dense core which left is the white dwarf and its surface will cool down slowly over the period of billions of years.
Epsilon Canis Majoris - Its name is Adhara. Its main component is a bright giant with visual magnitude of 1.5, its distance from Earth is about 450 light years, its mass is about 13 solar masses and its diameter is 14 solar diameters, with outer atmosphere temperature about 22,000 K. About 20 million years old.
The companion has visual magnitude of 7.5 separated about 7 arc seconds from the main component.
h 3945 - The visual magnitudes of the companions of this double star are 5.0 and 5.9. Their separation on the sky is about 27 arc seconds. It is a beautiful double star with great color contrast of the components. The colors of the components are orange and blue.
Deep sky objects
(can be observed only from dark location outside of the city)
M41 - Messier 41 from the Messier Catalog. It is an open cluster of stars with visual magnitude 4.5. It is visible with naked eyes from dark locations outside of the urban areas. It is about 2,300 light years away and its diameter is about 25 light years. About 200 million years old. Its brightest star is red giant with visual magnitude 6.3 located in the center of the cluster. Several red giants and also several white dwarfs are among the members of this cluster.
NGC 2360 - From the New General Catalog. It is an open cluster of stars with visual magnitude 7.2. It lies about 3,500 light years away and in reality its diameter is about 15 light years. It is about 2 billion years, and currently the stars with masses about 2 Sun masses have evolved into red giants.
NGC 2204 - From the New General Catalog. It is an open cluster of stars with visual magnitude 8.6. It is about 8,500 light years away from the Earth.
NGC 2362 - From the New General Catalog. It is an open cluster of stars. Its visual magnitude is 4.1 and it lies about 5,000 light years away. It is young cluster about 5 million years old. The stars which are members of this cluster are still on the main sequence, except one which is in the center of the cluster and stands out with its brightness among other members. It is the star Tau Canis Majoris with visual magnitude 4.9. It is a multiple star system with several close companions which can be resolved only with spectroscopy. The largest member have mass about 50 times that of our Sun and is the only star which evolved away from the main sequence. Currently is bright giant. Its diameter is about 20 times bigger than our Sun diameter. Other two stars which are part of this star system are also massive stars, but still on the main sequence with masses about 20 Sun masses each.