The constellation Cancer does not contain any bright stars. However, the constellation gave the name to the Northern Tropic of the Earth. Several astronomical objects in it deserve to be mentioned.
Zodiac Cancer
According to astrologers, the Sun will enter the constellation Cancer on June 22. Or perhaps on the 21st. There is no consensus among astrologers on this point. But astronomers are unanimous: it will enter this constellation only on July 21, that is, in just one month.
The reasons for this are described in this article, but they can be summarized as follows: astronomers look at the sky all the time, but astrologers use obscure methods that were outdated 2000 years ago to determine the position of astronomical bodies.
However, the power of tradition should not be underestimated. After all, this constellation, which astrologers consider “dark” due to the lack of bright stars, gave the name to the Northern Tropic of the Earth. The latter is an imaginary line that marks the northernmost latitude at which the Sun can be at its zenith.
This happens during the summer solstice, which occurs on June 21-22. This fact was discovered more than 2000 years ago, when our sun was actually in the constellation Cancer. Since then, precession has shifted this point relative to the stars, the very boundaries of the constellations have changed, but the name has remained, although now it does not correspond to the actual state of affairs. During the summer solstice, the Sun will still be in Taurus and only move to Gemini the next day.
In general, as with any constellation in which the Sun is located, the end of June is a very poor time for observing. Cancer is simply hiding in the rays of our luminary; it can be seen only slightly right after the Sun sets over the western horizon, but given the dimness of the stars in it, it is almost impossible to see anything now.
The best time to observe the constellation Cancer is in winter. Then it will rise high in the sky in the middle of the night. However, it will not be easy to find it. First, you need to find Gemini, then Leo, and then Cancer will be between them.
Cancer is a constellation that has been known since ancient times, but myths describe its appearance in the sky very briefly. Once upon a time, when Hercules was fighting the Hydra, a giant arthropod climbed out to help her. However, the hero defeated him, and the gods took both monsters to heaven.
Interesting stars
Often, the brightest star in a constellation is its α, and then the luminosity decreases from one letter of the Greek alphabet to another. However, in the case of Cancer, everything is as confusing as possible. The brightest star is its β, which has its name Tarf. However, even this star has a magnitude of 3.5, which means that it is hardly noticeable.
Tarf is located at a distance of 290 light-years from us. This is a double system consisting of an orange giant 51 times larger and 677 times brighter than the Sun and a red dwarf orbiting it at a distance of 2600 AU. This system makes a full revolution in 76 thousand years.
In 2014, scientists announced that a planet was orbiting the main component of β Cancri. This is a gas giant whose mass is 7.8 times that of Jupiter. It makes one revolution around the star in 605 days, but given the star’s luminosity, it must be much hotter than the Earth.
The second brightest star in the constellation Cancer is its δ, or Asellus Australis. It is also a multiple system. The brightest star is an orange giant, 11 times larger than the Sun in radius and 59 times larger in luminosity. Together with another companion, it forms a double system, and the third luminary orbits them.
The third brightest star in the constellation is γ Cancer, Asellus Borealis. It is a large white star located at a distance of 181 light-years from us. Its mass is 2.18, and its radius is 2.5 times that of the Sun.
Another very interesting star can be seen only if you have perfect eyesight or use binoculars. We are talking about 55 Cancri, which was given its name in the twenty-first century –Copernicus. It is a double system located at a distance of 40.9 light-years from us. Its main component is a sun-like star with a mass of 91% and a radius of 98% of that of our own.
The second component orbits it at a distance of 1065 AU. This is a red dwarf with a mass and radius equal to 26% of the solar mass. However, what makes this system interesting is the 5 planets orbiting the main star.
All of them are named after astronomers. The closest to the star is 55 Cancri e, also known as Janssen. It is a super-Earth that is 8 times as massive and 81% larger than our home planet in terms of radius. It makes one revolution around the star in just 17 hours, and its surface is heated to 3000°C.
Next is planet b, also known as Galileo, a hot gas giant with 82% of the mass of Jupiter. It makes one revolution around the star in just 15 Earth days. Then there is 55 Cancri c, or Brahe. This is a “hot Neptune” with a mass 51 times that of the Earth. It makes one revolution around the star in 44 days.
Another “Neptune” is 55 Cancri f, or Harriot. This planet has a mass 48 times that of the Earth and orbits its star in 260 days. The intensity of the radiation allows liquid water to exist, so if not it, then its satellites may be habitable.
The planet 55 Cancri d, or Lipperhey, is the farthest from the star. It has a mass 3.12 times that of Jupiter and makes one revolution in 14 Earth years.
Praesepe and М67
However, the most interesting object for amateur astronomers in the constellation Cancer is not a single or multiple star at all, but a diffuse cluster called the Praesepe, or Beehive Cluster (M44). It looks like a small foggy spot near δ and γ Cancer. Together with these two stars, it forms the Donkey asterism. The Praesepe is a large group of stars that share a common origin and travel through the Milky Way together.
The distance to the cluster is 577 light-years, and it includes about 1000 luminaries. The age of the cluster is 600-700 million years, which means that it is very young compared to the Sun. However, scientists have already discovered two planets around the stars that make up the cluster.
Another prominent cluster in the constellation of Cancer is M67. It consists of about 500 stars and is located at a distance of 2600 light-years from us. It is one of the oldest star clusters known to humans. Its age is estimated at 3.2 to 5 billion years.
Quasar OJ 287
The constellation Cancer is also interesting for its quasars, giant black holes located in the centers of galaxies that are billions of light years away. But we can still see them because they absorb a large amount of matter, and part of it is converted into radiation that we can see throughout the entire Universe.
In particular, OJ 287 is located in the constellation Cancer. This object is a lacertide, a special type of quasar characterized by high variability of light in all bands and bright emission lines.
OJ 287 is located at a distance of 4 billion light-years from us and is a pair of black holes. The larger of the two has a mass 18.35 billion times that of the sun, and the second has about 100 million solar masses. They orbit each other for 11-12 years.
