Horse-Related Constellations: Which is Which?
The names and forms of our constellations are inspired by different objects, animals, characters, and mythological creatures. Aside from the differences, we cannot help but notice some similarities among the 88 modern constellations of today. There are times when two constellations are represented by the same animal. We can think of the dog constellations Canis Major and Canis Minor as an example. We can also notice such similarities with the Monoceros constellation and other horse-like constellations. Let’s review which is which so that we can avoid confusing them with each other.
The Monoceros Constellation is also known as “the Unicorn.” A unicorn is a mythological creature. It looks like a common horse but with something extra—a horn! This single horn is often spiraled. We can see it in the middle of its forehead. The unicorn is a symbol of purity and grace so it is usually depicted in white color. In the sky, we can see the “Lesser Dog” of the Canis Minor constellation on the unicorn’s back.
The Pegasus constellation is also related to horses. It is called “the Winged Horse.” The major difference between Pegasus and a unicorn is that Pegasus does not have a horn and a unicorn does not have wings. Also, notice that Pegasus is the name of a certain character in Greek mythology while a unicorn is a common name for a mythological creature.
In the night sky, the Winged Horse appears upside down in relation to other constellations.
The Equuleus constellation is named the “little horse” or the “foal” of the celestial sky. Interestingly, this constellation is depicted with the head of a horse only. It is beside the constellation of Pegasus and it also appears upside down!
The Centaurus Constellation is called “the Centaur.” A centaur is a creature in Greek Mythology with the upper body of a man and the lower body of a horse.
The constellation of Sagittarius is also represented by a centaur, though it is known as “the Archer.”
The Monoceros constellation has many stars and deep-sky objects. Learning about it means running into some new words and terms. It will help us enjoy our journey of understanding our celestial unicorn if we are familiar with these concepts.
What is Apparent Magnitude?
The apparent magnitude tells us how bright an object is in the sky as observed here on Earth. This object can be a star or any deep-sky object. The apparent magnitude depends on the following:
1. An object’s luminosity (energy emitted from a star’s surface)
2. An object’s distance from Earth
3. Anything in between the object and the observer
Just remember that the smaller the magnitude, the brighter the object is, as seen here on Earth. The brightest star, Sirius, even has a negative apparent magnitude of −1.46.
What is a Variable Star?
A variable star is a star whose brightness keeps changing as we see here on Earth. The same concept applies to a variable nebula. The change in brightness in a variable nebula is caused by the changes happening in its stars. Variable stars and variable nebulae are mentioned a lot when learning about the many stars and deep-sky objects in the Monoceros constellation.
A star’s color tells us something about its age and temperature. Mainly, there are seven types of stars.
Blue stars (Class O) = the hottest and the youngest
Red stars (Class M) = the coldest and the oldest
M-type stars do not have much hydrogen left to burn, so they are not as hot as the blue ones anymore.
In Focus: Monoceros aka The Unicorn
The word “monoceros” means “unicorn” in Greek. Constellation Monoceros was not included in the 48 constellations of Ptolemy’s Almagest. Much about it is credited to Dutch astronomer and cartographer Petrus Plancius. He was responsible for introducing the unicorn constellation to the world. It first appeared on a globe he created in 1612.
In 1624, German astronomer Jakob Bartsch included the Monoceros constellation on his star chart. In that star chart, he named it “Unicornu.” Today, the unicorn constellation is one of the 88 modern constellations recognized by the International Astronomical Union (IAU). Out of those 88 constellations, Monoceros is the 35th largest. It covers an area of 482 square degrees.
What Does Monoceros Look Like?
The form of the Monoceros constellation can be different depending on sources. It can also depend on where we are when we look at the night sky. Take note of the lines connecting the stars in the pictures below.
Where and When To See the Monoceros Constellation
Right Ascension: 7 hours
Declination: -5 degrees
Latitudes: Between +75° and −90°
The Monoceros constellation lies on the celestial equator. Specifically, it is in the second quadrant of the northern celestial hemisphere (NQ2). It is between 75° and -85° latitudes. We can see it in the winter night sky. It is best visible to us during the month of February at 9 pm.
Monoceros and Its Neighbors
Finding the celestial unicorn in the night sky becomes easier because it is surrounded by many bright and big constellations. It is bordered by Hydra to the east, Orion to the west, Gemini to the north, and Canis Major to the south. Other neighboring constellations are Canis Minor, Puppis, and Lepus.
The Unicorn Inside the Winter Triangle
A big part of the celestial unicorn lies inside the Winter Triangle. The Winter Triangle is an asterism formed by three bright stars from neighboring constellations of Canis Major (Sirius), Canis Minor (Procyon), and Orion (Betelgeuse). This triangle can also help us in locating the Monoceros constellation.
Monoceros and Its Stars
The Milky Way passes through the Monoceros constellation. Because of that, it has many interesting stars and deep-sky objects. Let’s get to know some of them.
1. Alpha Monocerotis (α Monocerotis)
Alpha Monocerotis is the brightest star in the Monoceros Constellation. It is a red clump giant star. It generates energy at its core by helium fusion. We can see it in the naked eye because its apparent magnitude is 3.94. This G-type star is located 148 light-years away from the Sun. Alpha Monocerotis is 1.18 billion years old, having a mass twice our Sun.
2. Beta Monocerotis (β Monocerotis)
Beta Monocerotis is a triple star system that appears as a single star to our naked eye here on Earth. The combined magnitude of these three stars is about 3.74. William Herschel discovered it in 1781 and said that it is “one of the most beautiful sights in the heavens.” It is believed to be 700 light-years from Earth.
We can say that Beta Monocerotis is the brightest visible star in the Monoceros Constellation since we see Beta Monocerotis A, Beta Monocerotis B, and Beta Monocerotis C as one. All three components are B-class stars. If we look closely, these individual stars are not as bright as α Monocerotis. Alpha Monocerotis is still the brightest individual star in the Unicorn constellation.
● Beta Monocerotis A (β Monocerotis A)
Beta Monocerotis A has an apparent magnitude of 4.6. It is 3,200 times more luminous than the Sun and it has a mass of 7 solar masses.
● CCDM J06288-0702D is a visual companion of the triple star system near Beta Monocerotis A. Although, there is a chance that it just
looks close to each other here on Earth. Its magnitude is estimated to be 12.
● Beta Monocerotis B (β Monocerotis B)
Beta Monocerotis B has an apparent magnitude of 5.4. Its luminosity is 1,600 times our Sun’s, having a mass of about 6.2 solar masses.
● Beta Monocerotis C (β Monocerotis C)
Beta Monocerotis C has an apparent magnitude of 5.6. Its mass is about 6 solar masses. It is 1,300 times more luminous than the Sun.
3. Gamma Monocerotis (γ Monocerotis)
Gamma Monocerotis is a binary star that we can see with our naked eye. Its apparent visual magnitude is 3.96, making it the second brightest star in the Monoceros constellation. It is an orange giant of stellar class K1.5III. It is located 500 light-years from our Sun.
4. Delta Monocerotis (δ Monocerotis)
Delta Monocerotis is a single star. It is the third brightest star in the constellation of the celestial unicorn. This white-hued star has an apparent magnitude of 4.15. We can see with our unaided eye but it will be faint. Delta Monocerotis is 375 light-years from the Sun.
5. Epsilon Monocerotis (ε Monocerotis)
Epsilon Monocerotis is a binary star system. It is roughly 128 light-years from Earth, with an apparent magnitude is 4.31. It is on the west side of the Rosette Nebula. The components of this binary star are Epsilon Monocerotis A (ε Mon A) and Epsilon Monocerotis B (ε Mon B).
● Epsilon Monocerotis A (ε Mon A)
Epsilon Monocerotis A is an aging subgiant star. It has a white hue. The apparent magnitude of this primary component is 4.39. It is believed to be a spectroscopic binary. A spectroscopic binary is a system of two stars that are very close to each other. From our point of view, it is difficult to tell the two stars apart so a careful analysis is needed.
● Epsilon Monocerotis B (ε Mon B)
The second component is Epsilon Monocerotis B. This star has a yellow-white hue with an apparent magnitude of 6.72.
6. Zeta Monocerotis (ζ Monocerotis)
Zeta Monocerotis is a single star. It has a yellow hue, having an apparent visual magnitude of 4.37. We can see it in the night sky without using any telescope. It is 1,852 light-years from our planet, Earth. The luminosity of Zeta Monocerotis is 2,535 times more than the Sun. It has three visual companions, components B, C, and D. Their apparent visual magnitudes are 10.32, 9.68, and 13.4 respectively.
7. S Monocerotis
S Monocerotis is also called 15 Monocerotis. This variable star system is the brightest star in a deep-sky object in the Monoceros Constellation called the NGC 2264. S Monocerotis is also a multiple star system. It has many companion stars like S Monocerotis A and S Monocerotis B.
8. V838 Monocerotis
V838 Monocerotis is also known as Nova Monocerotis 2002. This spectroscopic binary star system has an original apparent magnitude of 15.6. It is about 20,000 light-years from Earth.
It was just an unknown star in the Monoceros Constellation before. But on January 6, 2002, this faint star started to brighten. It reached its maximum visual magnitude of 6.75 on February 6th, a month after its first outburst. It then started to dim, something that naturally happens in a nova explosion. During this time, a light echo was observed by NASA’s Hubble Space Telescope.
After some time, Nova Monocerotis 2002 showed some signs of activity again. It was something very interesting. It became super bright! At that time, V838 Monocerotis was one of the brightest stars in the Milky Way galaxy.
9. Plaskett’s Star
Plaskett’s Star is also called HR 2422 and V640 Monocerotis. A Canadian astronomer named John Stanley Plaskett discovered the binary system of this star in 1922, so it was named after him.
HR 2422 is a very massive binary system. Its total mass is about 100 times more than the Sun. Because of that, there was a time when it was considered the most massive binary system. The combined visual magnitude of components A and B of V640 Monocerotis is 6.05.
CoRoT-7 is also known as TYC 4799-1733-1. It is a yellow dwarf star, which is a little smaller and cooler than our Sun. It is 500 light-years from our planet, Earth. This is a faint star, having an apparent visual magnitude of 11.67, so it is not visible in our naked eye. Some exoplanets (planets outside the Solar System) are discovered to orbit CoRoT-7.
CoRoT-1 is a G-type kind of star. Its temperature and mass are closely similar to our Sun. It is a very dim star, having an apparent visual magnitude of +13.6. It is about 2,630 light-years away. An exoplanet known as CoRot-1b orbits this star.
12. 13 Monocerotis
13 Monocerotis is known as 13 Mon for short. This white supergiant star in the Monoceros Constellation has an apparent magnitude of 4.5. It is about 2,500 light-years away.
13. HD 48099
HD 48099 is another spectroscopic binary in the constellation of the celestial unicorn. Its apparent magnitude is 6.37. Both of its components are O-type stars. The two stars in HD 48099 only take about three days to complete one orbit.
14. HD 46375
HD 46375 is a K-type subgiant star. This star is older than the Sun and is starting to become a red giant. Its apparent magnitude is 7.84, and it is 114 light-years from the Sun.
Formally Named Stars
There are two stars in the Monoceros Constellations that are formally named and approved by the International Astronomical Union (IAU).
● Citalá (HD 52265)
Citalá is a G-type main-sequence star. This star in the Monoceros constellation is 98 light-years away from us. It is more massive and more luminous than our Sun. It is estimated to be about 2.6 billion years old. An exoplanet called HD 52265 b orbits this star.
The formal name of HD 52265 was selected during the100th year anniversary of the International Astronomical Union (IAU). Citalá means “River of stars.” It is from the Nahuat language, a language native to El Salvador in Central America.
● Lusitânia (HD 45652)
Lusitânia is also called HD 45652. This star in the constellation Monoceros is 114 light-years from us. Its apparent magnitude is 8.13.
The Nearest Black Hole
V616 Monocerotis is also known as 1A 0620-00 or A0620-00. This binary star system in the constellation Monoceros is different from its other stars. The two objects of A0620-00 orbit each other. One of them cannot be seen. The mass of this invisible component is six times more than the mass of our Sun.
Astronomers believed that this massive star system is a black hole. With a distance of about 3,300 light-years, V616 Monocerotis was the nearest black hole to our planet.
As of 2020, a black hole in the HR 6819 star system was discovered. It is just 1,011 light-years away, making it the new closest black hole to Earth ever known. It lies in the Telescopium Constellation.
Planets in Monoceros Constellation
The constellation of the celestial unicorn also hosts extrasolar planets (exoplanets), or planets outside our Solar System. Some of them are considered super-Earths. When we say that a planet is a super-Earth, it means that it has a mass higher than that of the Earth’s. It does not say anything about its surface conditions, or whether it can sustain life.
CoRoT-7b was named CoRoT-Exo-7b before. This exoplanet in the Monoceros constellation is 489 light-years from Earth. This super-Earth orbits around the star CoRoT-7.
CoRoT-7c is another exoplanet orbiting the G-type star CoRoT-7 in the constellation Monoceros. It is also a super-Earth, having a distance of about 489 light-years away.
CoRoT-7d is the third exoplanet of the star CoRoT-7, but it is still unconfirmed. It is said to be 489 light-years away from our solar system.
CoRoT-1b is an exoplanet in constellation Monoceros orbiting the star CoRoT-1. It is 2,630 light-years away from us.
5. HD 52265 b
HD 52265 b is 98 light-years away from us. This exoplanet is a gas giant. It orbits the star HD 52265, which is also named Citalá. The minimum mass of this exoplanet is slightly more than the planet Jupiter’s. HD 52265 b is named Cayahuanca. The name is from the native Nahuat language which means, “The rock looking at the stars.”
Cayahuanca was discovered by two independent teams namely the California and Carnegie Planet Search team and the Geneva Extrasolar Planet Search team.
Deep-sky Objects In Monoceros Constellation
There are lots of interesting deep-sky objects in the constellation of the celestial unicorn. Let us get to know about its Messier objects, Caldwell objects, and many more.
The Messier Catalogue was compiled by a French astronomer named Charles Messier. He made the list not because of interest in deep-sky objects. These non-comet objects were getting in the way of his study about comets. There are 110 Messier objects in total. Most of the deep-sky objects in the Messier catalogue are easy to see from the night sky of the northern hemisphere.
There is only one Messier object in the Monoceros constellation.
1. Messier 50 (M50)
Messier 50 is also known as NGC 2323. It is roughly 3,000 light-years away from Earth. This open cluster has 508 confirmed members. M50 is about 140 million years old. It is located near the Canis Major constellation, which is located south of Monoceros.
The Caldwell catalogue is another astronomical catalogue. It contains a total of 109 star clusters, galaxies, and nebulae. What makes this list great is that it was made for observation purposes, especially for amateur astronomers.
The Caldwell catalogue was named after the other surname of Patrick Moore. He was the one who compiled the list. Moore made sure to include the brightest deep-sky objects. Also, he noted that a lot of bright deep-sky objects in the Southern Hemisphere were not included in the Messier Catalogue.
The Caldwell objects in the catalgoue were named in a way that C1 is the northernmost object and C10 is the most southerly.
There are four Caldwell objects in constellation Monoceros.
1. Caldwell 46 (C46)
We can call Caldwell 46 using many other names. It is also called NGC 2261 or Hubble’s Variable Nebula. It was discovered by William Herschel in 1783. Caldwell 46 was the first astronomical image taken by the Hale Telescope at Palomar Observatory. Its name, Hubble’s Variable Nebula, was after Edwin P. Hubble. He made a lot of early studies on this object.
Caldwell 46 is illuminated by one of the stars in the unicorn constellation called R Monocerotis. This star lights up the gas and dust nearby. One reason why C46 is a variable nebula is because those clouds of dust sometimes block the light from R Monocerotis, creating a shadow.
2. Caldwell 49 (C49)
Caldwell 49 is also called the Rosette Nebula. In the New General Catalogue, it is known as NGC 2237. It is located in a giant molecular cloud in the Monoceros constellation where the Milky Way passes through. It has a diameter of 130 light-years. The Rosette Nebula is 5,000 light-years away from Earth. There are many new-born stars inside this nebula.
● Caldwell 50 (C50)
Caldwell 50 is also called NGC 2244 or the Satellite Cluster. This open cluster is in the Rosette Nebula. It has many O-type stars. NGC 2244 is said to be 5 million years old.
3. Caldwell 54 (C54)
Caldwell 54 is also called NGC 2506. It is an open cluster of stars that is mildly-elongated. It is one of the four Caldwell objects found in constellation Monoceros. The cluster of NGC 2506 is about 2 two billion years old. Around 94 members were identified to be within its field.
Other Deep-Sky Objects
The constellation of Monoceros has many fascinating astronomical objects. One reason for that is because the Milky Way (the Celestial River) passes through it. Some of these objects are nebulae. Remember that a nebula is a formation of gas and dust. It is like the nursery for the formation of new stars!
1. NGC 2264
NGC 2264 is a diffuse nebula. A diffuse nebula is an extended nebula which does not have a definite boundary. NGC 2264 refers to both the Christmas Tree Cluster and the Cone Nebula as one astronomical object. All the objects in this nebula are 2,600 light-years from Earth.
● The Christmas Tree Cluster
The Christmas Tree Cluster is an open cluster made up of very young stars. It got its name because of its triangular shape which makes us think of our favorite tree, the Christmas tree! It makes up NGC 2264’s northern part.
● The Cone Nebula
The Cone Nebula is on the southern part of one of the famous NGC 2264. It got its name from its cone-like shape. Its apparent length is 10 arcminutes. A massive star known as NGC 2264 IRS gave rise to the creation of many baby stars in the Cone Nebula.
Two other deep-sky objects are in the NGC 2264 region, but they were not officially included. They are the Snowflake Cluster and the Fox Fur Nebula.
● The Snowflake Cluster
The Snowflake Cluster is another amazing cluster in NGC 2264 of the Monoceros constellation. It is made up of infant stars that appear as pink-red specks toward the center. This star-forming cloud is dynamic because its newborn stars are going to crawl away from their birth location as time goes by. When that happens, the snowflake-like structure of these stars will not resemble its cluster name anymore.
● The Fox Fur Nebula
The Fox Fur Nebula is near the brightest star in NGC 2264, which is the S Monocerotis. It got its name because it looks like a red fox stole (shawl). We can see both blue and red areas of this nebula.
2. IC 447
IC 447 is a reflection nebula. A reflection nebula is made up of clouds of interstellar dust that reflects the light of stars nearby. It contains some massive B-type stars.
3. The Red Rectangle Nebula
The Red Rectangle Nebula is also called HD 44179. We can easily identify it in pictures because of its red color and rectangular shape. It has a binary star in its center but they are hidden, so we cannot see its light. There is still a lot of mystery about the Red Rectangle Nebula. Its X-shape is just one example.
4. NGC 2232
NGC 2232 is another open star cluster in the Monoceros constellation. It is 1,060 light-years from the Sun. It is one of the closest open clusters to our Sun.
5. The Seagull Nebula
The Seagull Nebula is also called IC 2177. It is about 3,650 light-years away from Earth. Many stars form in this cosmic cloud. It is between the border of the Monoceros constellation and the Canis Major constellation. Some astronomers think that IC 2177 resembles a lizard when the image is going to be rotated 180 degrees. The area near the seagull’s eye (or head) is called NGC 2327.
● NGC 2327
NGC 2327 has a cluster of stars born more than one million years ago. The Seagull’s eye is the hottest and brightest area in the entire Seagull Nebula.
Meteor Showers Related to Monoceros Constellation
1. Alpha Monocerotids
Alpha Monocerotids run from November to December. During its peak on December 21, we can see as many as 12 meteors per hour. This meteor shower is also called the November Monocerotids.
2. December Monocerids
December Monocerids happen every year from November 9 to December 11. We cannot see as many meteors during its peak on December 8, where only two meteors or less fall per hour.
More About Monoceros and Unicorns
There is still more to know about the Monoceros constellation after learning about its location, stars, and other deep-sky objects. It is always better to learn something extra!
Monoceros Constellation in Urania’s Mirror
Urania’s Mirror is a set of 32 astronomical star-chart cards. It is also called “A view of the Heavens.” It was first published in 1824. These cards have holes so that when we hold it against the light, we can see the stars of the constellations shining bright!
In the 31st star-chart card (Plate 31) are the constellations of Monoceros, Canis Minor, and Atelier Typographique. The third constellation might sound unfamiliar. That is because this constellation does not exist anymore!
Atelier Typographique or Officina Typographica was located south of Monoceros. The constellation was drawn to honor Johannes Gutenberg’s printing press. This constellation’s most recent use was in 1878. The stars of Officina Typographica became a part of the Puppis constellation. It became permanent there when the constellation boundaries were set in 1928.
Unicorns in Ancient Times
The Monoceros constellation is relatively new so there is no mythology directly related to it. We might not hear stories about why it was put in the night sky, but unicorns have been mentioned a lot throughout time. Some early artworks of Mesopotamia showed unicorn-like creatures. Below is a unicorn seal.
Here is a unicorn-like creature found in Lascaux cave paintings, in south-western France. It is said to be about 17,000 years old.
The unicorn was also mentioned in some of India and China’s ancient myths. It was introduced into Greek Literature by Ctesias, a historian. It was said to have healing powers, as everyone who drank from its horn will be protected from harm.
In the Bible, an animal called re’em was mentioned a lot. Some translated this creature as “unicorn.” Many stories surround this mythical creature.
Some stories said that the reason why there are no more unicorns on Earth now is because they were busy playing when the animals were boarding Noah’s Ark. Whatever the truth is, the mystery of this creature is still stirring the curiosity of many up to this day!