Stars magnitude

Stars magnitude

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I have a question: assume two identical stars, but one is 10 times farther than the other from the earth. If the nearest star has a relative magnitude of 5, what is the relative magnitude of the other?

As @RobJeffries mentions, you can calculate the difference from the equations which define magnitude and flux. But this particular case is even covered in the Wikipedia article on apparent magnitude:

For objects within the Milky Way with a given absolute magnitude, 5 is added to the apparent magnitude for every tenfold increase in the distance to the object.

So if the nearest star has magnitude 5, the farthest one has magnitude 5 + 5 = 10.

Stars magnitude - Astronomy

The magnitude system is a scale to show how bright stars appear. The initial magnitude system was developed by the Greek astronomer, geographer, and mathematician Hipparchus (190 BC to 120 BC). He ranked stars by their apparent brightness, with 1 being the brightest and 6 being barely visible, without the telescope or other optical aid.

He also designed his original magnitude scale, such that the star Polaris, the northern hemisphere’s pole star, would have a magnitude of 2. Hipparchus’ initial magnitude scale was revised by Norman Pogson in 1856. Pogson specified a 1st magnitude star is 100 times brighter than a 6th magnitude star. Based on Pogson’s system, a 1st magnitude star is 2.512 times as bright as a 2nd magnitude star. With this revision also came inclusion of brighter objects, such as the Sun and Moon, and fainter objects then visible through the telescope. What we see in our sky is called an object’s Apparent Magnitude, M v.

Questions about star magnitude.

Some one asked me what the dimmest star in one of my images. I had no idea. After annotating the image in pixinsight I picked star Th YC 4461-604-1. Then went to the SIMBAD online database and got the data (below).

Does the Fluxes data refers to the colors (wavelengths measured) and there corresponding brightness?

Does the "K" value stand for white (all combined colors)?

So If the stars magnitude was reported it would be10.909?

Attached Thumbnails

#2 munkacsymj

Those letters (B, V, G, J, K, H) refer to photometric bands, with the brightness in magnitude after the letter and the measurement uncertainty in square brackets.

V = "visual" (a slightly reddish green)

G = green (a little bluer than V)

J = Infrared (centered at 1220 nm)

H = Infrared (centered at 1630 nm)

K = Infrared (centered at 2190 nm)

The "V" magnitude is probably the best match to what the human eye would see. For the star you've quoted from SIMBAD, that would be magnitude 11.81.

Now, as to the faintest star in your image, I looked at the star that you've flagged with the red line (GSC 04461-00365), which is about magnitude 11.5. I went in to Aladin and pulled up the region around that star and zoomed in, picking one of the faintest stars visible in your image (the star that I circled in yellow from the Digital Sky Survey image below):

That star is listed in the Gaia EDR3 catalog as being magnitude +17.8

I don't claim that this is the faintest star in your image, but it's in the general ballpark.

#3 SeymoreStars

Those letters (B, V, G, J, K, H) refer to photometric bands, with the brightness in magnitude after the letter and the measurement uncertainty in square brackets.

B = blue

V = "visual" (a slightly reddish green)

G = green (a little bluer than V)

J = Infrared (centered at 1220 nm)

H = Infrared (centered at 1630 nm)

K = Infrared (centered at 2190 nm)

The "V" magnitude is probably the best match to what the human eye would see. For the star you've quoted from SIMBAD, that would be magnitude 11.81.

Now, as to the faintest star in your image, I looked at the star that you've flagged with the red line (GSC 04461-00365), which is about magnitude 11.5. I went in to Aladin and pulled up the region around that star and zoomed in, picking one of the faintest stars visible in your image (the star that I circled in yellow from the Digital Sky Survey image below):


That star is listed in the Gaia EDR3 catalog as being magnitude +17.8

I don't claim that this is the faintest star in your image, but it's in the general ballpark.

- Mark

People like yourself, sharing their time and knowledge, make this hobby worthwhile and a joy.

Science and religion versus slavery

Miniature of emancipated slave Bilal, Islams first Muezzin.

Before examining the contributions of Arab astronomy, a few words about the intimate link between Islam and the development of science.

According to tradition, it was in 622 CE that the Prophet Muhammad and his companions left Mecca and set out for a simple oasis that would become the city of Medina.

If this event is known as the “Hegira”, an Arabic word for emigration, break-up or exile, it is also because Mohammad broke with a societal model based on blood ties (clan organization), in favor of a model of a shared destiny based on belief. In this new religious and societal model, where each person is supposed to be a “brother,” it is no longer permissible to abandon the poor or the weak as was the case before.

The powerful clans in Mecca did everything they could to eliminate this new form of society, which diminished their influence.

The “Medina Constitution” allegedly proclaimed equality among all believers, whether they were free men or slaves, Arabs or non-Arabs.

The Koran advocates strict equality between Arabs and non-Arabs in accordance with the Prophet, who said, in his farewell address:

“There is no superiority of an Arab over a non-Arab, or of a non-Arab over an Arab, and no superiority of a white person over a black person or of a black person over a white person, except on the basis of personal piety and righteousness.”

(Reported by Al-Bayhaqi and authenticated by Shaykh Albani in Silsila Sahiha no. 2700).

Hence, if after the Prophet’s death, slavery and slave trade became a common practice in close to all Muslim countries, he cannot be held accountable. Zayd Ibn Harithah, according to tradition, after having been the slave of Khadija, Muhammad&rsquos wife, was freed and even adopted by Muhammad as his own son.

For his part, Abu Bakr, Muhammad&rsquos companion and successor as the first Caliph (Arab word for “successor”), also freed Bilal ibn-Raba, the son of a former Abyssinian princess who had been enslaved. Bilal, who had a magnificent voice, was even appointed the first muezzin, that is to say the one who calls for prayer five times a day from the top of one of the mosque&rsquos minarets.

The Sultan Ahmed Mosque, popularly known as the Blue Mosque, in Mazar-e-Sharif, Balkh Province, Afghanistan.

Among the first verses revealed to the Prophet Muhammad one finds :

Read! And your Lord is the Most Generous, Who taught by the pen Taught man that which he knew not.”

(Surat 96).

The best among you (Muslims) are those who learn the Koran and teach it.”

Other sayings, often attributed to the Prophet, clearly invite Muslims to seek knowledge and cherish science :

The ink of the scholar is more sacred than the blood of the martyr”.
Seek knowledge from the Cradle to the Grave”.
Seek knowledge even as far as China”.

Historical center of Samarkand (Ouzbekistan). The Registan and its three madrasahs. Astronomical and mathematical notations. Manuscript page from Timbuktu .

The mosque is much more than a place of worship, it is a school of all sciences, where scholars are trained. It serves as a social and educational institution: it may be accompanied by a madrassa (Koranic school), a library, a training center, or even a university.

As in most religions, in Islam, practices and rituals are punctuated by astronomical events (years, seasons, months, days, hours). Every worshipper must pray five times a day at times that vary depending on where he or she is on Earth: at sunrise (Ajr), when the sun is at its zenith (Dhohr), in the afternoon (Asr), at sunset (Magrib) and at the beginning of the night (Icha). Astronomy, as a spiritual occasion to fine-tune one’s earthly existence according to the harmony of the Heavens, is omnipresent.

As an example, to underscore its importance, July 16, 622, the first day of the lunar year, was declared the first day of the Hegira calendar. And during the eclipse of the sun, mosques host a special prayer.

Islam encourages Muslims to guide themselves by the stars. The Koran states :

And He is the One who made the stars for you to guide you with them in darkness of the land and the sea”.

With such an incentive, the early Muslims soon perfected astronomical and navigational instruments, and even today more than half of the stars used for navigation bear Arabic names. It was only natural that the faithful constantly tried to improve astronomical calculations and observations.

The first reason is that during the Muslim prayer, the worshipper has to prostrate himself in the direction of the Kaaba in Mecca, so he has to know how to find this direction wherever he is on Earth. And the construction of a mosque will be decided according to the same data.

The second reason is the Muslim calendar. The Koran states :

The number of months in the sight of Allah is twelve (in a year)- so ordained by Him the day He created the heavens and the earth of them four are sacred: that is the straight usage.”

Clearly, the Muslim calendar is based on the lunar months, which are approximately 29.5 days long. But 12 times 29.5 days is only 345 days in the year. This is far from the 365 days, 6 hours, 9 minutes and 4 seconds that measure the duration of the rotation of the Earth around the Sun…

Finally, a last challenge was posed by the interpretation of the lunar movement. The months, in the Muslim religion, do not begin with the astronomical new moon, defined as the moment when the moon has the same ecliptic longitude as the sun (it is therefore invisible, drowned in the solar albedo) the months begin when the lunar crescent starts to appear at dusk.

The Koran says: “(Muhammad), they ask you about the different phases of the moon. Tell them that they are there to indicate to people the phases of time and the pilgrimage season.”

For all these reasons, the Muslims could not be satisfied with either the Christian or the Hebrew calendar, and had to create a new one.

A multitude of phenomena—such as the chemical enrichment of the Universe, the mass spectrum of planetary nebulae, white dwarfs and gravitational wave progenitors, the frequency distribution of supernovae, the fate of exoplanets, etc.—are highly regulated by the amounts of mass that stars expel through a powerful wind. For more than half a century, these winds of cool aging stars have been interpreted within the common interpretive framework of 1D models. I here discuss how that framework now appears to be highly problematic.

• Current 1D mass-loss rate formulae differ by orders of magnitude, rendering contemporary stellar evolution predictions highly uncertain. These stellar winds harbor 3D complexities that bridge 23 orders of magnitude in scale, ranging from the nanometer up to thousands of astronomical units. We need to embrace and understand these 3D spatial realities if we aim to quantify mass loss and assess its effect on stellar evolution. We therefore need to gauge the following:

• The 3D life of molecules and solid-state aggregates: The gas-phase clusters that form the first dust seeds are not yet identified. This limits our ability to predict mass-loss rates using a self-consistent approach.

• The emergence of 3D clumps: They contribute in a nonnegligible way to the mass loss, although they seem of limited importance for the wind-driving mechanism.

• The 3D lasting impact of a (hidden) companion: Unrecognized binary interaction has biased previous mass-loss rate estimates toward values that are too large.

Only then will it be possible to drastically improve our predictive power of the evolutionary path in 4D (classical) spacetime of any star.

Ancient Astronomers

Ancient astronomers could only estimate magnitudes. However, modern astronomers can measure the brightness of stars to high precision. Consequently, they have made adjustments to the scale of sizes. Instead of saying that the star known by the name Chort (Theta Leonis) is the third magnitude, they say it is magnitude 3.34. Accurate measurements show that some stars have a brighter size than 1.0. For example, Vega (alph Lyrae) is so bright that its magnitude, .004, is almost zero. Some stars generate negative numbers on the scale due to the brightness. On this scale, Sirius, the brightest star in the sky has a magnitude of -1.47.

Modern astronomers have had to extend the faint end of the magnitude scale as well. The faintest stars you can see with your unaided eyes are about the sixth magnitude. Meanwhile, if you use a telescope, you may see stars that appear much fainter. Astronomers must use magnitude numbers larger than 6 to describe these faint stars.

Messier Catalog: M1 - M10

M1 Supernova Remnant in Taurus
Common Names: Crab Nebula
NGC Number: 1952
Visual Magnitude: 8.4
ra: 5h 34.5m
dec: +22° 01' M2 Globular Cluster in Aquarius
Common Names: None
NGC Number: 7089
Visual Magnitude: 6.5
ra: 21h 33.5m
dec: -0° 49' M3 Globular Cluster Canes Venatici
Common Names: None
NGC Number: 5272
Visual Magnitude: 6.2
ra: 13h 42.2m
dec: +28° 23' M4 Globular Cluster in Scorpius
Common Names: None
NGC Number: 6121
Visual Magnitude: 5.6
ra: 16h 23.6m
dec: -26° 32' M5 Globular Cluster in Serpens
Common Names: None
NGC Number: 5904
Visual Magnitude: 5.6
ra: 15h 18.6m
dec: -32° 13' M6 Galactic Cluster in Scorpius
Common Names: Butterfly Cluster
NGC Number: 6405
Visual Magnitude: 5.3
ra: 17h 40.1m
dec: +2° 05' M7 Galactic Cluster in Scorpius
Common Names: Ptolemy's Cluster
NGC Number: 6475
Visual Magnitude: 4.1
ra: 17h 53.9m
dec: -34° 49' M8 Diffuse Nebula in Sagittarius
Common Names: Lagoon Nebula
NGC Number: 6523
Visual Magnitude: 6.0
ra: 18h 03.8m
dec: -24° 23' M9 Globular Cluster in Ophiuchus
Common Names: None
NGC Number: 6333
Visual Magnitude: 7.7
ra: 17h 19.2m
dec: -18° 31' M10 Globular Cluster in Ophiuchus
Common Names: None
NGC Number: 6254
Visual Magnitude: 6.6
ra: 16h 57.1m
dec: -4° 06'


Christian scientists assert that materialistic explanations of the origin of stars are errant and contra-evidence and reports of stars forming are invalid. [21] [22] [23] [24] [25] In addition, creationists cite the secular scientific literature in order to make the case that materialist explanations of star formation are inadequate:

“We don’t understand how a single star forms, yet we want to understand how 10 billion stars form.” Carlos Frenk, as quoted by Robert Irion, “Surveys Scour the Cosmic Deep,” Science, Vol. 303, 19 March 2004, p.�. [26]

“Nobody really understands how star formation proceeds. It’s really remarkable.” Rogier A. Windhorst, as quoted by Corey S. Powell, “A Matter of Timing,” Scientific American, Vol. 267, October 1992, p.㺞. [27]


Luminosities are expressed as magnitudes. The ancient astronomers recorded apparent magnitudes into the groups: bright, intermediate, and faint. These three groups would be sub-divided into a 6-category system and each group would become known as a magnitude. Each magnitude was brighter or fainter than the next magnitude by an approximately constant but undetermined factor, which is now known to have been of the order of 2.5. The apparent magnitude of a star reflects the apparent luminosity. The absolute luminosity is defined on a similar scale, with the distance taken as 10 parsecs: 2,000,000 astronomical units, about ten times the actual distance to the star nearest the Sun. Magnitude scales give brighter stars a lower numerical magnitude and fainter stars, a higher numerical magnitude. The brightest stars have apparent magnitudes near 0, the faintest stars seen by the eye are 6th magnitude. Absolute magnitudes range from 15 (faintest) to -10 (brightest).

Distances can be determined, for stars near the Sun, using the parallax method. Given apparent magnitude and distance, the absolute magnitude can be calculated.

Astronomers plotted apparent magnitude versus spectral type (roughly, stellar surface temperature), but found only a disordered scattering of points that seemed to mean nothing. However, as distances became available, spectral type was plotted versus absolute magnitude: a quite distinctive pattern appeared, which meant that there were physical laws ruling the origin and evolution of stars. The Hertzsprung-Russell diagram (the HR diagram) has become a key interpretive tool, indispensable for discussing the history of stars.

Stars magnitude - Astronomy

Question 1: Which is the brightest of the first magnitude stars?
Answer: Sirius at magnitude -1.46
An easy question to start with, although the answer does assume a definition of the term “first magnitude star” which requires some explanation. The magnitude scale was first invented by the Greek astronomer Hipparchus in the second century BC. He simply divided all of the stars in the sky into six categories depending on their apparent brightness. The brightest stars were of the first magnitude, the next brightest of the second magnitude and so on down to the faintest visible stars which were of the sixth magnitude in Hipparchus’ system. This was pretty much all there was to say on the subject for a very long time. The invention of the telescope at the start of the seventeenth century however, made it apparent that there were many millions of stars fainter than the sixth magnitude and by the middle of the nineteenth century, with the subject of astronomy advancing rapidly it was realised that there was a need for a more formal definition of stellar brightness that allowed for a continuous range of possible values, rather than just six discrete numbers. Early photometric measurements established that a first magnitude star is about 100 times as bright (based on measured incident light flux) as a sixth magnitude star and in 1856 Norman Pogson used this fact to adapt Hipparchus’ system to produce the magnitude scale that is still in use today. Pogson’s scale is logarithmic, with every interval of one magnitude equating to a variation in brightness by a factor of just over 2.5 times. Based on this continuous scale, any star with a magnitude of between 5.5 and 6.5 is now considered to be of the sixth magnitude, any star with a magnitude of between 4.5 and 5.5 is considered to be of the fifth magnitude and so on. Under this logic a first magnitude star ought to have a magnitude in the range 0.5 to 1.5. The problem is of course that there are nine stars with magnitude lower than 0.5 and the scale even has to be extended into negative territory to cater for the four brightest. However it would be rather pedantic of me to inform you that Betelgeuse and not Sirius is the brightest of the first magnitude stars. It is customary therefore to extend the definition of a first magnitude star to be any star with a magnitude lower than 0.5. There is one remaining caveat and that is (for a reason that should be obvious): to be considered first magnitude, a star must also be more than 93 million miles away!

Question 2: Which is the faintest of the first magnitude stars?
Answer: Regulus at magnitude 1.35
Regulus is the faintest of the 21 stars that satisfy the above definition. At one stage a 22nd star – Adhara in Canis Major was also thought to be of the first magnitude. The most recent measurements however have moved Adhara’s magnitude back from 1.49 to 1.50, so that it is relegated once more to head the list of second magnitude stars. The constellation of Canis Major therefore has the distinction of possessing both the brightest first and the brightest second magnitude star.

Question 3: Which is the closest first magnitude star?
Answer: Rigil Kentaurus (Alpha Centauri) at 4.4 light years (about 26 trillion miles)
The distance to Alpha Centauri was first determined by the Scottish astronomer Thomas Henderson in 1839. He used the only direct technique available for measuring distances in space, namely that of trigonometric parallax. Because of the vast distances of the stars, measurement of stellar parallax had eluded astronomers for many centuries until Friedrich Bessel’s famous breakthrough with 61 Cygni in 1838. Henderson’s measurements on Alpha Centauri were actually made earlier than those of Bessel but he did not manage to reduce his data until some months after Bessel had already gone to print.

Question 4: Which is the furthest first magnitude star?
Answer: Deneb at about 1,600 light years
Deneb is so far away that its parallax is too small to be obtained by methods currently at our disposal, so 1,600 light years is simply our current best estimate of its distance. Following the pioneering efforts of Bessel, Henderson and others such as Struve in the mid-19th century, Earth based astronomers over the next 150 years only managed to push the parallax method out to about 50 light years with any sort of accuracy. A huge leap forward came in 1989 with the launch of ESA’s “Hipparcos” satellite, whose name honours that great astronomer of antiquity and is an acronym of the somewhat contrived mission title: “High Precision Parallax Collecting Satellite. Hipparcos accurately measured the parallax of over a million stars, 120,000 of them with unprecedented, milliarcsecond accuracy and pushed the limit for the parallax method out to at least 500 light years.

Apart from Deneb only three other first magnitude stars were believed prior to Hipparcos to lie at distances greater than this and in each case the Hipparcos measurements led to a substantial change in the estimated distance. Rigel moved in from 900 to 733 light years, Betelgeuse moved in from 520 to 427 light years and Antares moved out from 520 to 604 light years.

Question 5: How many constellations have more than one first magnitude star?
Answer: Three (Orion, Crux and Centaurus)
Only three of the 88 constellations possess as many as two first magnitude stars. All the others have one or none. The three are Orion (with Rigel and Betelgeuse), Centaurus (with Rigil Kentaurus and Hadar) and Crux (with Acrux and Mimosa). As noted above, Canis Major comes close to being a fourth.

Question 6: Which pair of first magnitude stars are closest together?
Answer: Acrux and Mimosa (Alpha and Beta Crucis)
The two brightest stars of Crux (the Southern Cross) are just over four degrees apart, fractionally closer together than the next closest pair, Rigil Kentaurus and Hadar (Alpha and Beta Centauri), which themselves lie less than ten degrees away from the Crux pair in the southern sky.

Question 7: Are there more first magnitude stars north or south of the celestial equator?
Answer: There are 11 south of the celestial equator and 10 to the north
The southern skies are therefore marginally better endowed than the northern skies in terms of first magnitude stars. However the fact that the three brightest stars in the sky, Sirius, Canopus and Rigil Kentaurus all lie well south of the celestial equator (with the latter two never visible from the UK), leaves Northern Hemisphere observers feeling they have much the worst of the deal.

Question 8: Which are the most northerly and southerly first magnitude stars?
Answer: Capella (46o North) and Acrux (63o South)
The Southern Hemisphere also comes off best in terms of circumpolar stars (i.e. those that never set and therefore can be seen all night, every night). Whereas only Capella, Deneb and Vega are circumpolar from the Midlands of England, five stars are circumpolar from Sydney and Cape Town. These are the Crux and Centaurus pairs and Achernar in Eridanus. From much of New Zealand these five are comfortably above the horizon all of the time and also joined by Canopus.

Question 9: Which is the best season for seeing first magnitude stars?
Answer: Winter (with 8 stars)
The answer to this question is of course more subjective than some of the others, but it’s probably fair to say that a greater number of first magnitude stars are at their most prominent during Winter than at any other time of year. The eight normally regarded as winter stars are the six stars Sirius, Rigel, Aldebaran, Capella, Pollux and Procyon which form a rough hexagon surrounding a seventh, Betelgeuse, together with Canopus to the south.

Question 10: Which is the poorest season for seeing first magnitude stars?
Answer: Autumn (with just two: Fomalhaut and Achernar)
Again this is a matter of opinion but most observers would probably agree that autumn skies are the most barren in terms of bright stars. Dividing the remaining eleven first magnitude stars between Spring and Summer is likely to provoke more debate, since Arcturus and the two Centaurus stars can be considered borderline. However antipodean astronomers will probably consider the question rather academic since, as already noted, the latter two are for many of them circumpolar.

Question 11: How many of the first magnitude stars are variable?
Answer: Only Betelgeuse is markedly variable (ranging between magnitude +0.2 and +1.2), although another five are usually listed as variable and many of the others (probably the majority) are slight or suspected variables
For the record, the five other definite variables are: Aldebaran, Antares, Spica, Hadar and Mimosa.

Question 12: How many of the first magnitude stars are binary or multiple systems?
Answer: At least 13 – between 40 and 50 suns contribute to the light of the 21 first magnitude stars
The systems with the most members are Aldebaran, which is thought to have at least three dwarf companions and Capella which is a close binary orbited by a dwarf star which is itself double. The Acrux system also may have four components, although it is uncertain whether the fourth member is gravitationally bound to the others. Known triple stars in the list include Rigil Kentaurus, whose faintest member, the 11th magnitude red dwarf Proxima Centauri is the closest individual star of all, apart from our own Sun. Proxima Centauri is so distant from its two much brighter companions that it may only be a temporary member of that system. Famous doubles amongst the first magnitude stars include Sirius which has an eighth magnitude white dwarf companion. In the answers to the remaining questions I have ignored those members which do not contribute a significant percentage of the total light output of their system.

Question 13: Which first magnitude star has the shortest rotational period?
Answer: Altair rotates in 10 hours (compared with 25 days for the Sun)
Altair has a rotational velocity of 210 kilometres per second which is about 100 times that of the Sun. The extremely rapid rate at which the Altair is spinning about its axis causes it to bulge at the equator and Altair’s equatorial diameter is thought to be about 14% greater than its polar diameter. Even more extreme is Regulus, with a rotational velocity of about 350 kilometres per second and a bulge of 35%. The fact that Regulus is a larger star than Altair (about 3.5 times the Sun’s diameter compared with 1.5 times for Altair) means that it has a longer rotational period of about 16 hours. Even Regulus is not the most distorted star: Achernar, about 10 times as large as the Sun, rotates with a velocity slightly faster than that of Altair which causes it to distort by a massive 56%. Achernar is shedding significant amounts of material as a result of its rapid rotation, but it is calculated that it would need to be spinning twice as fast in order to disintegrate completely. At the other extreme Aldebaran is thought to have one of the lowest rotational velocities, possibly similar to that of the Sun meaning that with a diameter of over 40 times that of the Sun it may take as long as two years to rotate once about its axis, although there appears to be considerable uncertainty about this. The largest stars probably have rotational periods of many years, but despite this one of them, as we shall see later, is probably even more misshapen than Achernar.

Question 14: Which first magnitude star has the greatest proper motion?
Answer: Rigil Kentaurus (3.69 arcseconds per year)
As might logically be expected the closest star to us is the one that is moving fastest across our line of sight, although it still takes as much as 1,000 years to change its position by as much as one degree, relative to the other stars in the sky. The really interesting question is: which one is second fastest? Plotting the proper motions of the first magnitude stars against their distances in light years, one sees the expected rapid decrease until beyond 100 light years, values are typically below 0.1 arcseconds per year.

Watch the video: Ο άνθρωπος μέσα από τα μάτια της αστροφυσικής. Pavlos Kastanas. TEDxTechnicalUniversityofCrete (May 2022).