The Terebellum Star– Facts in brief:
What is it?
This faintly visible Fixed Star named Terebellum (Omega Sagittarii, 58 Sagittarii (its Flamsteed designation) is one of the many stars within the well-known and relatively large Constellation of Sagittarius. Terebellum is not actually part of the main outline of the Constellation of Sagittarius.
It is recognized as the 28th brightest Star in the celestial Archer Constellation, and although its luminosity is faint it is still visible by the naked eye.
Terebellum, is a mature main sequence star that can be described in two ways:
- a yellow spectroscopic binary star, spectral type G3/G5lll
- a yellow subgiant star , spectral type G5 IV
It is a suspected variable yellow subgiant star, located in the Constellation Sagittarius, which is located in the Southern Hemisphere.
It is identifiable as a part of one of the more prominent asterisms in the sky known as ‘The Tetrapleuron’ (translated as Terebellum).
Terebellum is located close to the celestial equator and it is therefore partly visible from both the northern Hemisphere and the Southern Hemisphere, in the night sky, at certain times of year.
It can mainly be seen from the Southern Hemisphere from June to November, but can also be seen low on the horizon in the months of August to October in the Northern Hemisphere.
Terebellum in Sagittarius
Terebellum (omega Sagittarii) is a spectroscopic binary star.
It’s yellow in color and located in the Constellation Sagittarius, in the Southern hemisphere, but visible from both (and associated with the image from Greek Mythology, The Archer).
It is the 28th brightest star in Sagittarius, after 27 other bright stars that also have a fourth magnitude rating.
- Kaus Australis, is the brightest star in Sagittarius, with an apparent magnitude of 1.79, located 143 light years from the Sun and visible by naked eye in the night sky
The Constellation of Sagittarius is the 15th largest Constellation overall in the Southern Sky and borders several other well known, and easy to identify Constellations:
The age and size of Terebellum
Based on its spectral type of G3/G5lll the color of this star is yellow.
This suggests that it has exhausted all of the hydrogen at its core and has therefore evolved beyond the main sequence stage of a star’s life.
This is a hot star that has expanded over time and was estimated, according to the latest Hipparcos data in 2007, to have 3.12 times the radius of the Sun (expanded to a radius of 3.12 solar radii), and emits around 7.1 times as much energy.
It is estimated by Hipparcos to be around 2.6 billion years in age (from a possible range of 2.30-2.90 billion years old), but it is not known how much longer its lifespan will be.
It is possible that it will continue to expand and possibly end life in a supernova explosion.
The luminosity of Terebellum is not bright enough for it to be listed as one of 58 bright stars commonly used for celestial navigation and marking our position. (The brightest Star in the Constellation of Sagittarius, Kaus Australis, epsilon Sagittarii, with its apparent magnitude of 1.73 is ranked number 48 of the 58 listed Navigational Stars)
FACT: The Navigational stars are some of the brightest and most easily recognized stars in the night sky. They were used by many ancient civilizations during sea voyages and from land points to mark time, locate their position and plan directions for journeys.
Ptolemy’s Quadrilateral asterism
It was Ptolemy who used the name ‘Tetrapleuron” translated as Terebellum, to describe this asterism, a quadrilateral of 4th magnitude stars he observed in the Constellation of Sagittarius.
These four stars are located within 2 degrees of each other and form a visible quadrilateral shape with one star at each former as follows:
- Terebellum I, Omega Sagittarii – located in the North East corner
- Terebellum II, 59 Sagittarii, located in the South East corner
- Then Terebellum III, 60 Sagittarii, is located in the North West corner
- Terebellum IV, 62 Sagittarii, located in the South West corner
The Terebellum I is considered to be the chief bright star in the quadrangle. In Greek mythology it is referred to as the quadrangle in the tail, referring to the rump of the Archer figure associated with the Sagittarius Constellation.
These fixed stars are located within the Constellation Sagittarius and are close to the eastern border of the Constellation Capricornus.
The star names in the asterism often referred to as The Quadrilateral include:
- Omega Sagittarii,, a yellow subgiant, with an apparent magnitude of 4.70, located 76 light years distant from the Sun
- 62 Sagittarii, (its Flamsteed designation) an aging single, variable red star, and the brightest star within the Quadrilateral, with an apparent magnitude of 4.43, located 450 light years from the Sun
- 59 Sagittarii (its Flamsteed designation), a single star, with an apparent magnitude of 4.54 located 830 light years from the Sun
- 60 Sagittarii, (its Flamsteed designation),the dimmest of the four, is a suspected binary star is located 379 light years distant from the Sun, with an apparent magnitude of 4.83
Greek Mythology – Terebellum is positioned within Sagittarius, which is known as the Archer and also known as the Centaur according to the Greek myth. This star is not positioned on the main outline of the Constellation but on the rump of the tail instead (on a creature that is half man and half horse)
Characteristics of this yellow giant star
Terebellum is a binary system, with a subgiant star and a companion of uncharacterized status.
The brightness of Terebellum is only used as the guide point for other Constellations, asterisms or stars, when it is viewed as part of the asterism known as the Terebellum Quadrilateral, as on its own it is a faint star.
It is a spectroscopic binary star, with a fourth magnitude rating (apparent magnitude 4.7 and absolute magnitude 2.64), and a surface temperature of between 5,000 and 6,000 Kelvin, at the latest estimate, giving it a similar luminosity to the Sun, which is estimated to be 5,775K. It is visible by naked eye.
Terebellum (omega Sagittarii) is a Fixed Star.
The latest Hipparcos distance estimate in 2007 for this dim yellow subgiant star locates it around 84.76 light years from Earth (around 25.99 parsecs), and 76.4 light years from the Sun (23.4 parsecs).
FACT: 1 light year equals 0.3066 parsecs
However we now know that everything moves around in space, the planets orbit stars and the stars orbit the galactic center.
Terebellum’s Galacto-Centric distance is 24,061.07 light years (7,377.00 parsecs).
It is now located about 5,360,784.96 Astronomical Units from the Earth/Sun, according to the 2007 Hipparcos distance data.
The proper motion movement of stars away from/to the Sun is measured in milliarcseconds.
If the measure is negative it means the star is moving closer to the Sun, and if the number is positive it means the star is moving away from the Sun.
Terebellum is moving 209.41 milliarcseconds east (away from the Sun) and 62.39 milliarcseconds north (away the Sun).
The Radial Velocity is the speed at which the star is moving either away from or towards the Sun, and with a projected velocity of -39.14000 km/s it is drifting closer to the Sun.
It is positioned near the ecliptic which means it is subject to lunar occultation.
Who named the stars?
In 1603, the German Astronomer – Johann Bayer, systematically assigned names to the brightest stars in each constellation and cataloged them in his Star atlas – ‘Uranometria Omnium Asterismorum’.
The Bayer designations are stellar designations where the stars within Constellations such as Constellation Sagittarius, are initially identified by a name or a letter from the Greek Alphabet from Alpha through Omega (in order of brightness).
1. The names of the Stars begin with a letter of the Greek alphabet starting with – Alpha, then beta, gamma, etc.
2. Followed by the genitive form of the Sagittarius parent constellation’s Latin name- ‘Sagittarii’, sometimes abbreviated to ‘Sgr’.
Johanne Bayer did not assign the alpha name to the brightest star in Sagittarius; instead he assigned the epsilon name to this star.
The main sequence stars of Sagittarius are listed by their apparent magnitude (luminosity) from Earth, listed from the brightest to faintest star in decreasing order. Those with an apparent magnitude of less than 3.00 are:
1. Kaus Australis, epsilon Sgr, is a binary system star and the most luminous star in Sagittarius, with a luminous apparent magnitude of 1.79, and 145 light years distant
2. Nunki, Sigma Sgr, is a single star and the second brightest star in Sagittarius with a visual/apparent magnitude of 2.05
3. Ascella, Zeta Sgr, a triple star system and third brightest Star with a visual/apparent magnitudeof 2.60
4. Kaus Media, Delta Sgr– a double star, the fourth brightest star with a variable magnitude of 2.72
5. Kaus Borealis, Lambada Sgr – the fifth brightest component in Sagittarius and is a single star, with a visual magnitude of 2.88
6. Al Baldah, Pi Sgr, a triple Star System , with an apparent magnitude of 2.89
7. Alnasi, Gamma Sgr, a double star, with an apparent magnitude of 2.98
Where is it in the shape of Sagittarius?
The outline of the Constellation of Sagittarius is in the shape of an Archer with a bow and arrows (or the Greek mythical Centaur), and Terebellum represents a part of the tail on this creature.
The traditional name ‘Terebellum’,of the star omega Sagittarii, has been officially recognized by the International Astronomical Union (IAU).
The Constellation of Sagittarius has a total of 17 formally named stars, including Terebellum which are approved by the IAU, including:
- Ainalrami, Ablaldah, Alnasl, Arkab Posterior, Arkab Prior, Ascella, Belel, Gumala, Kaus Australis (the brightest star), Kaus Borealis, Kaus Media, Nunki, Pincoya, Polis, Rukbat, Sike and of course, Terebellum
Properties of the Terebellum Star
Terebellum is a massive star, classified as a yellow subgiant star, and the 28th brightest star in the Constellation Sagittarius. It islocated approximately 84.76 light years distant from Earth.
The Ecliptic runs through the Constellation of Sagittarius, and as the star named Terebellum is so close to the ecliptic it is prone to be occulted by the Earth’s Moon.
The members of the Terebellum star system are known to orbit each other every 4.6892 light years
Terebellum, within the Constellation of Sagittarius, is located towards the center of the Milky Way Galaxy, and roughly:-
- South of the Constellations Aquila, Scutum and Serpens Cauda
- East of Capricornus
- North of the Constellations Telescopium, Corona Australis and Scorpius
Generally the rate at which stars evolve depends on their mass. The greater the mass the quicker the star evolves from the main sequence.
The mass of the sun, referred to as its stellar mass, and enumerated as the Sun’s mass as a proportion of solar mass.
The mass of the Terebellum star components is much bigger than the Sun. It is estimated to be around 165 times more massive, quantified as around 1.65 solar masses. It has strong stellar winds which means it can lose mass quickly.
The surface gravity of Terebellum is 3.64 cgs.
The Terebellum Star has a solar radius of 287 times that of the Sun, referred to as 2.87 solar radii.
How bright is this Star
Terebellum, the yellow subgiant star is a fourth magnitude luminous star when viewed from Earth.
Its luminosity is the amount of energy emission from this subgiant star relative to the Sun.
Its luminosity is estimated to have a similar brightness to that the Sun.
The brightness of a star as seen from earth is measured by its magnitude of which there are three classifications: Apparent Magnitude, Visual Magnitude and Absolute Magnitude.
The measurements for the brightness of Terebellum are:
- An apparent magnitude (also referred to as its visual magnitude) of +4.70
- An absolute magnitude of 2.64
FACT: The Apparent Magnitude is how bright we see a Star from Earth, and the Absolute Magnitude is the Apparent Magnitude of that star from a 10 parsecs distance (32.6 light years), assuming there are no molecular clouds, or dust in the line of sight.
The lower the number of magnitude the brighter the Star.
The color of the Terebellum Star
The Terebellum Star is classified as a subgiant Star, which according to its spectral type, G3/G5lll, is a yellow colored star.
The surface temperature of this yellow subgiant star
Based on the spectral type of this Star it is estimated to have a surface temperature of between 5,000-6,000 degrees Kelvin. This makes it one of the hotter Stars in the Universe, and similar to the surface temperature of the Sun.
Where is it located? –
The distances vary depending on how it’s measured and there are certainly margins of error.
According the latest 2007 Hipparcos measurement the parallax data gave an uncertain result. The Terebellum Star is estimated to be around 84.76 light years (25.99 parsecs) from Earth.
FACT: A parallax is a difference in the apparent position of a star or any solar system object viewed from two different lines of sight. The parallax is measured by the angle between the two lines of sight.
The distance between the Earth and the Sun is known as an Astronomical Unit. The figure of A.U. is calculated as the number of times that Star is from Earth, in relation to the Sun. It is estimated that the Terebellum Star is approximately 5,360,784.96A.U. from Earth to Sun in distance.
FACT: All Stars and Planets orbit round a central point, the planets orbit the Sun and the Stars orbit the Galactic Centre.
The Star Terebellum is located approximately 24,061.07 light years (7,377.00 parsecs) from the Galactic Center, the center of the galaxy we call the Milky Way.
The Galacto-Centric distance is measured as the distance from that Star to the center of the Galaxy (Sagittarius A).
Fact: the Galactic Center, or Galactic Centre, is a supermassive black hole and the rotational center of our Milky Way galaxy. It is not possible to view it at visible, ultraviolet, or even soft or low-energy X-ray wavelengths because of the molecular clouds of interstellar dust along its line of sight.
Where can it be seen?
As we have already discussed, the Terebellum Star is one of the 17 main Stars in the Constellation Sagittarius and a star you can see by the naked eye. It is of great interest to amateur astronomers as it is visible as part of the Tetrapleuron asterism, a quadrilateral of 4 stars, and points towards the large mythical sea-goat shape of the Constellation Capricornus.
Co-ordinates of a right ascension, or left ascension and their declination are used to locate all of the notable objects in the sky
The Terebellum Star lies at a 19 hours 55 minute right ascension, and a declination of -26 degrees.
The right ascension – is the angular distance of any sky object along the celestial equator from the March (Spring) equinox.
- If it has a positive number it is east of the March equinox.
The declination – is the angle of the sky object from the celestial equator.
- If it has a negative number it indicates it is located in the Southern Hemisphere
Terebellum is located close to the celestial equator and is therefore partly visible from both the northern hemisphere and the southern hemisphere at certain times of year.
The age of the Terebellum Star
It is not certain what age the Star Terebellum is or how long it is likely to continue to survive. One estimate of the age of this Star is that it is still young and possibly around 2.6 billion years old.
How can you identify the Terebellum Star?
The simplest method for spotting any particular Star from Earth is to first of all locate an easy to recognize neighboring Constellation or object in the night sky.
Sagittarius is probably one of the easiest to spot as it is formed from some very bright stars in a distinctive pattern- the archer that appears to be half man and half horse, with Terebellum positioned on the high point of the tail.
The Greeks saw it as a mythical creature called a Centaur. It is located near the celestial equator and that means it is visible in most of the world.
It is sometimes referred to as ’The Teapot’, with a prominent handle and spout, beside the curved body of Scorpius. Other stars in this mythical image include W Sagittarii – as the nozzle of the Teapot
The best time of year to spot the Terebellum star from a Northern sky is in the evening sky is during July, August and early September in the Southern Hemisphere, and in the northern part of the sky if south of the equator.
Deep Sky Objects
FACT: A Deep Sky Object is an astronomical object, that is not a solar system object like the Sun, Moon, Comet or a Planet.
Individual Stars, are not considered to be Deep Sky Objects.
Deep Sky Objects are faint objects that can still be observed by the naked eye in the night sky from Earth.
- Star clusters – such as Globular Clusters of Stars or Open Clusters of Stars
- Dark Nebula, Planetary Nebula, Diffuse Nebula, Reflection Nebula and Supernova remnants
- Galaxy Groups, Galaxies, Spiral Galaxies, Gravitational Lenses and Quasars
The area of the sky where the Constellation of Sagittarius is located if highly populated with deep sky objects so there is lots of interesting objects to spot. To spot most of them though, you will need a good telescope for deep space objects.
How do we obtain the images and measurements of Stars from Space?
Images of the different Stars and nebulae have been captured using a professional large telescope, such as the NASA Spitzer Space Telescope, with a near infrared camera and multi-object spectrometer, all covered by Wikipedia sources.
The standard measurement of distance for Stars for decades has been using the ESA Earth-orbiting Hipparcos satellite, which replaced the ESA Gaia mission to chart a three dimensional map of the Milky Way Galaxy.
ESA Gaia measured the positions and radical velocities of around one billion stars in our galaxy.
The celestial pole
The celestial pole defines the poles of the celestial equatorial coordinate system.
An object at the Celestial pole has a declination of 0 degrees.
- The declinations for the north celestial pole is +90 degrees
- The declinations for the south celestial pole is -90 degrees
The celestial poles are not permanently in a fixed position against the background of the stars as everything moves in Space.
The Terebellum Star is located in the Southern celestial sky at a -26, 17’ degrees declination, and an average 19 hours, 55 min right ascension.
Fun Facts about Stars – Did you know that?
- The name Terebellum has several meanings. Derived from Latin, meaning a borer or auger, as in a tool. It is used in astronomy to describe the asterism in the Constellation of Sagittarius.
- The name Terebellum is also used in reference to marine gastropods, is an edible genus of sea snails within the family Seraphsidae, the Terebellum conchs. They are a part of the superfamily – Stromboidea.
- Terebellum is sometimes referred to as HD 188376
- It is listed as HIP 98066 in the Hipparcos Star Catalogue
- After the Sun, Sirius is the brightest star in the sky with an apparent magnitude of -1.46
- The Star we call The Sun does not belong to any constellation
- The planet Jupiter is often cited when making size comparisons between planets or stars. The Jupiter mass is a unit of mass equal to the total mass of planet Jupiter
- The rate of formation of stars in a starburst galaxy is more than 10 times faster than the star formation in the Milky Way galaxy
- The center of a Galaxy does not contain a Giant Star it contains a Supermassive Black Hole.
- A Red Dwarf is not a Dwarf Planet it is a Star. Most common Stars are Red Dwarf (cool Stars)
Commonly Asked Questions
Q. What prevents us seeing the Stars in the night sky?
A. Light pollution, fog, city lights and artificial lights all limit our visibility of the objects in the sky at night.
Q. Will the locations of Stars change over time?
A. Stars are continually on the move.
The images we form in our imagination to make objects, shapes and patterns out of the constellations have already shifted over time.
As we view the night skies from Earth they are likely to continue to shift and possibly in time the images may look very different.
- Terebellum Star – https://theskylive.com/sky/stars/star-images/75/7597_800.jpg
- Terebellum color – https://nineplanets.org/wp-content/uploads/2020/02/Omega_Sagittarii.png
- Supernova Remnant – Cassiopeia A. Credit: NASA/CXC/SAO – https://scitechdaily.com/lonely-origin-of-cassiopeia-a-revealed-one-of-the-most-famous-supernova-remnants
- Celestial Pole – By I, Dennis Nilsson, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=3262268