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Astronomical Observations & Research

Ruby Star Realm of the majestic "Ruby Star" in Taurus
- by A. Ahad

Article posted: 19 October 2004

Copyright 2004 Abdul Ahad. All rights reserved.

A Previously Unsung Red Supergiant

In the famous zodiacal constellation of Taurus there shines a rather 'un-famous' faint, naked eye variable star known by the inconspicious catalogue designation of 119 Tauri or CE Tauri. Under clear skies during winter evenings in the northern hemisphere, the star can be easily spotted with the unaided eye just a couple of degrees below the lower horn of the Bull - marked by the bluish white star Zeta Tauri.

To the naked eye, 119 Tauri appears quite dim and really nothing too much to write home about. However, take a look at it through a pair of simple binoculars or a small telescope and you immediately notice its majestic ruby red colour intensity.

One evening in late April, shortly after sunset as I was scanning the western sky under conditions of strong twilight with a pair of binoculars, the star briefly caught my glance. My initial reaction was "WOW" and I instantly recalled that no red star listings had ever shown a star of that degree of redness in that part of the sky.

Later that same evening, I spent several hours on the internet consulting various star catalogues and online articles, searched through books and star atlases to find out more about this wonderful little "gem" that I had accidentally stumbled upon in my celestial wanderings. As it turned out, the star never featured in a single red star listing anywhere, and I became the *FIRST* to identify 119 Tauri as the *second* reddest star in the entire night sky to shine consistently at a naked eye brightness well above the 5th magnitude. Hence my inspiration to call this THE "Ruby Star" as first discussed here! :)

The night sky's reddest stars plotted on magnitude vs colour index [Image: Abdul Ahad]
Above: The night sky's reddest stars plotted on apparent magnitude versus colour index - click to see a larger image. [Abdul Ahad]

That ranking of the Ruby Star as *the* second reddest star in the whole night sky shining consistently above magnitude 5 is an analytical "optimisation" between colour index ('B-V' on the UBVRI Johnson photometric system) and brightness (V-magnitude). This is indicated by the diagonal dotted line on the above chart, running from the lower left toward the upper right.

The variable stars U Hydrae and TX Piscium both have a higher colour index than either the Garnet Star or my Ruby Star and peak just above magnitude 5, but they spend most of their lives substantially below the brightness of both the Garnet and Ruby stars.

Although the Ruby Star has been on view since pre-historic times and telescopically studied for centuries, I was rather surprised that no one had either remarked on its colour intensity or included it in any red star listings. Of course, really well known brighter stars in a similar league to the Ruby Star like Betelgeuse (in Orion) and Aldebaran (in Taurus itself) have been universally acknowledged for their redness and noted in texts of ancient civilizations dating back to antiquity.

Abdul Ahad's Ruby Star in Taurus [Sky photographic credit:  T. Credner & S. Kohle, AlltheSky.com]
[Above image credit: T. Credner & S. Kohle, AlltheSky.com]

I had no hesitation in including the Ruby Star as the second observational entry in my red stars catalogue, after William Herschel's Garnet Star (Mu Cephei) which I had been observing for decades.

And why did I choose to call this newly identified gem the "Ruby Star"?
Well somehow, through some magical combinations of the star's intense red colour, its sparkling secondary colours produced by scintillation and its setting at the precise moment of my observation against a bright, twilight sky backdrop, all conspired to create such a breathtaking view that it was very much a case of 'love at first sight' !

A ruby in the terrestrial gemstone markets is regarded as the 'stone of love'. It symbolizes love, it emanates warmth and a strong sense of life. For thousands of years the ruby has been considered one of the most valuable gemstones of our planet, sparkling with an overwhelming brilliance. It is the undeniable King of Gemstones. The "celestial" ruby that I have identified in the sky mirrors these same qualities when seen through a small telescope.

Basic Facts on the Ruby Star in Taurus:-

  • Visual magnitude: 4.3 - 4.8 (Irregular pulsating variable)
  • Spectral type: M2Ib (Red supergiant)
  • Distance: 2,000 light years
  • Luminosity: 50,000(?) x Sun's luminosity
  • Colour index (B-V): +2.07
  • Surface temp: 3,500 K

Ruby Star [Image: Enchanted Learnings website] A Close Encounter with the Ruby Star

It is no wonder that hardly anyone on Earth has sung the praises of Ruby Star up to now, since it shines down to us so faintly from across roughly 2,000 light years of interstellar space. But imagine just how awesome the star would look from close up. With an intrinsic luminosity of some 50,000 times that of our own Sun, the Ruby Star would be a true 'celestial searchlight', dominating the night skies for scores of light years around its neighbourhood.

Imagine a futuristic scene looking ahead a few hundred thousand years from now (such imaginings may be rather difficult!) where a human colony has ventured two thousand light years from Earth to a region of space somewhere between the Orion and Perseus arms of our great Milky Way spiral galaxy. For that is where the Ruby Star reigns in the context of its broader galactic setting. In a view looking down on the spiral arms of the Milky Way from high up above the galactic plane, the Ruby Star might appear as one of the more exceptional ruby red gemstones set within a celestial "necklace" studded with a relatively large abundance of yellow/orange gems, countless white diamonds and a few occasional sapphires...

Suppose the future colony from Earth, upon arrival in the neighbourhood of the Ruby Star, decides to build a settlement on one of its far orbiting planets. Its inhabitants would surely experience an utterly alien scene on such a world each and every day, where the Ruby Star would bathe the entire planetary landscape in the most intensely reddish "sunshine" ever imaginable! To any children born to a family settled on that world orbiting the Ruby Star there would be nothing peculiar in this of course, since they will never have known another place to compare their familiar surroundings with. What may appear alien to us in the hear and now, in an alternate, future reality existing in a different space-time reference frame things could be totally natural and homely. That's a scary thought...

The Ruby Star seen from one of its orbiting planets [Picture courtesy: James Gitlin]
Above: Ruby Star rises with a ghostly shimmering glow above the eastern horizons of one of its far orbiting planets

Of course, there is a strong possibility that by the time humanity reaches the Ruby Star (if ever) in the unimaginable aeons of time ahead from now, it may have extinguished itself out in the most catastrophic supernova explosion to have happened this side of the Milky Way's core since Kepler's Star of 1604!

Analysing Ruby Star's Neighbourhood

And now onto some equations...
The absolute magnitude of a star (denoted 'M' in astronomy texts) is its visual magnitude when seen from a standard distance of 10 parsecs (32.6 light-years). It is a measure of a star's true (intrinsic) brightness and is related to its apparent magnitude 'm' and distance 'd' by the equation:-

M = m + 5 - 5 * Log10(d / 3.2616)
[m = apparent visual magnitude, d = distance in light years]

Thus, based on the latest Hipparcos astrometry measurements, the Ruby Star is thought to lie at an estimated distance of 2,000 light years from Earth and it shines at an average, apparent visual magnitude of +4.4 in our skies, hence its absolute magnitude would be about -4.5 (on average).

Now, the above equation can be re-arranged via some simple algebraic manipulations so that it lets us calculate the apparent magnitude 'm' of a star when seen from a distance of 'd' light-years:-

m = M - [5 - 5 * log10(d / 3.2616)]

This equation is very useful in the context of this article on the Ruby Star. Firstly, imagine how far from the star a planet needs to be to maintain liquid water and life supporting temperatures on its surface. (This is 'life' as in a human colony temporarily visiting a planet orbiting the Ruby Star as opposed to life actually *evolving* there, which would be unthinkable given the evolutionary phase the star is currently at in its life cycle).

Now, the Sun shines at a magnitude of -26.8 in our day time skies here on Earth from a distance of 1 AU. By comparison, the distance at which a planet would experience this level of light flux around Ruby Star would be between 60 to 75 AUs. The lower and upper limits of this calculated distance range corresponds to the star's apparent magnitude range from +4.3 to +4.8, which we see from Earth as Ruby Star pulsates as a red supergiant approaching the end of its life. For a planet circling at a fixed orbital distance from the star, the level of day time "sunshine" would therefore fluctuate pretty dramatically in line with the star's magnitude variations. In fact, the 0.5-magnitude amplitude would make the midday "sun" appear 60% more intense during Ruby Star's maxima compared to its minima...and the periodicity between such variations would be semi-regular to completely irregular.

In a second scenario, to get an appreciation of how "majestic" it would look from a closer distance, imagine if the Ruby Star were placed at the distance of where Alpha Centauri is today, at just 4.3 light years from us. Its apparent brightness in our night skies will then be a phenomenal -8.5 to -9.0 ! That's on average 60 times as bright as the planet Venus ever shines at its maximum brilliancy. Just imagine how red it would have looked, had it been at this relatively close distance from Earth. The star would have been readily visible in broad daylight in our skies and cast strong shadows at night.

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Betelgeuse - a star in the same league as the Ruby Star

My Catalogue of the Reddest Stars in the Night Sky

Copyright 2004 Abdul Ahad. All rights reserved.