Your Lucky Star – Astronomical Considerations

Every person is born under a celestial object. It might be a star, Cluster or Nebulae. The last two are referred to as Deep Sky Objects (DSO). In this Blog I am writing about stars only. Whether a birth star is a Lucky Star or not depends on two considerations: One relates to astronomy; the other relates to cosmics. Astronomy is based on observational and calculated data. Unlike in the case of other physical sciences it cannot be proved by exact evidence or precision. For example, the distance between the Earth and the Sun is about 93 million miles. Nobody ever did physically measure it anyway. However, astronomical data throws a lot of light and perhaps insight upon the impact and influence the stars have on you and me. The following are a broad brush stroke of the chief astronomical considerations about your birth star.

1. Visual Magnitude: It is also referred to as apparent magnitude. Conventionally written as lower case "m or V". This is a measure of brightness of a star as you see it from the earth. You can see stars up to 6^th magnitude by naked eye. Beyond 6^th magnitude you can see them using telescope only; hence the term telescopic stars. The scale of brightness runs from 0 to 25. As the scale goes higher the stars become dimmer and fainter. Sometimes we use the scale with minus value. This relates to extreme brightness. In the case of negative value as the value goes lower the extreme brightness shoots up.
   Visual magnitude ignores the distance of the star from the earth. As you are aware, the brightness of a star is the function of its internal energy generation and the quantum of light it emits into space. A good example is Sirius, the dog star, which is some 26 times brighter than the Sun, but being almost 9 light years way it appears to us dimmer than the Sun.
2. Absolute Brightness; In order to evaluate absolute brightness of stars, astronomers have set –up a standard. They place stars as if they were located 32.6 light years away. When we do this the scale of absolute brightness would read as follows: The Sun is 4.8, whereas Sirius 1.4 . Hence Sirius is about 3.4 times brighter than the Sun. Absolute Brightness is conventionally written as upper case "M or Mv". It is alternatively known as Real Brightness. For purpose of analysis absolute brightness is preferred over visual magnitude.

1. Spectral Class: This is a system of classification based on the spectrum of a star. Astronomers see a star and observe an emission line from which they can surmise the co-relation of the surface temperature with its colour. Generally we talk about 7 spectral types given as O,B,A, F,G,K,M. A useful mnemonics is Oh Be A fine girl And Kiss Me. I give below surface temperature, colour of each classes and a specimen star that goes with it.
   
   Class Surface Temperature (Kelvin) Colour Specimen
   O 30,000 to 50,000 Blue Alnitak
   B 10,000 to 30,000 Blue to White Rigel
   A 7,500 to 10,000 White Altair
   F 6,000 to 7,500 White to Yellow Pherkad
   G 5,000 to 6,000 Yellow Procyon
   K 3,500 to 5,000 Orange Altarf
   M Less than 3,000 Red Antares
   
   
   Each spectral class is further sub-divided into a scale of 0 to 9. For Example: the Sun is G2 star whereas Rigel is B8 star.
   
   
   
   
2. Luminosity: This is very much linked to Absolute Brightness. Luminosity stands for total brightness including the quantum of light and energy a star emits into the space, along with other aspects such as wavelengths and electro - magnetic radiation. Luminosity is given in Yerkes Class in Roman Numbers and was developed by the University of Chicago, Yerkes Observatory.
   Class Type
   I a Very luminous super giant
   I b Luminous super giant
   II Luminous giants
   III Giants
   IV Sub-giants
   V Dwarfs
   VI Sub-dwarfs
   VII White Dwarf
   
   Super giants are very large stars. Betelgeuse is an example. White dwarfs are smaller than our Earth. Sirius B and Ruiz are good examples.
   On the subject of spectrum there is one more thing must to be noted. Astronomers observe the line of emission carefully and describe peculiar details (if any) surrounding such line of emission. Usually, this peculiarity is given in lower case. The following are few of these:
   
   e for emission lines present
   k for intersteller absorption features
   m for enhanced metallic
   n for nebulous due to spinning
   p for peculiar
   q for red and blue lines present
   s for sharp absorption lines
   v for variable features
   w for weak lines
   
   
   Now you can read the notation of any star and find out what it means. Here are some examples:
   
   

• Deneb Adige, A2Iae : White 2 very luminous super giant, with emission lines present
• Castor, A2Vm : White 2 Dwarf with enhanced metallic
• Alpheratz, B8IVmnp : Light blue 8 sub-giant with enhanced metallic, nebulous due to spinning and peculiar emission

1. Light Year: Stars are too far away. Hence we use a system known of light years (l/y) to indicate their distance. A light year is the distance light travels in one year in a vacuum. It is estimated as a staggering 5,880,000 million miles. The closest star to our earth is Alpha Centauri C which is approximately 4.3 l/y away whereas. In contrast , Vega is about 25 l/y away.

1. Size of a star: This generally means the Radius of a star, which is presumed to be a function of luminosity and temperature. The radius of the Sun is 432,163 miles. The radius of Algenib is more than 2 million miles, which is about 4.5 times that of the sun. Hence we write it as "4.5 SolarR".
   
   

1. Mass of a star: This is arrived at after using the law of gravity. In order to attempt this analysis, we need to compare a star with its companion. Fortunately for us, majority of stars do have such companions. About half of the star population are binaries. Many others are double stars. The mass of stars vary in a scale from 0.08 of the Sun to more than 100 times of the Sun. For example, Mirzam has a mass of 15 times that of the Sun, conventionally written as "15M Sun".

1. Age of a star: The age of any star is just an estimate only. The Sun is approximately 4.5 billion years old. It has 5 Billion years left before its potential death as a star. Compared to this Alnitak is about 6 billion years old.
   
   
2. Companions: Stars like humans beings have never been single. They have relationship with one or more stars. Such relationship takes several forms:
   1. Double star: Two stars that appear to us on the earth as if close to each other. Acubens is a double star one is white and the other is red.
   2. Binary Star: A binary is two stars that rotate around a common centre. Alpha Centauri A & B are binaries
   3. Multiple star system: This consists of double stars or binaries or even ternary. There are two types. First, it may have physical relationship with a binary or a star that orbits it. Second, it may be an optical issue, that is we see them close to each other but there is no gravitational relationship established. Regulus is a multiple star system.

1. Variable stars: a star whose brightness varies regularly. This variation takes place once in few minutes or in months or in years. Algol for example varies every 2.9 days whereas Mira does so every 330 days.

1. Motion of a star: There are two types of motion.
   
   
   
   
2. Proper motion: Also known as Real Motion. All stars have motion in relation to each other in the space. Likewise our Milky Way also has motion. In fact the entire Universe and the Cosmos are in motion. We calculate proper motion of a star by observing its position over a period of time. Proper motion is generally given as units of arc second for year. The star with the fastest motion is Bernard's star with 10 seconds of arc per annum.
3. Radial motion: This motion relates to the position of the star to or from the Earth. Some stars proceed towards the earth. Example Mu Cassiopeia which approaches the Earth 61 miles per second. Many others move away from the earth. Aldebaran, for example, recedes from earth 30 miles per second.

1. Main Sequence star: This type of stars generates energy by converting hydrogen into helium at the core. Our Sun is a main sequence star. The hotter they are the brighter. Most of these are Dwarfs as per Yerkes classification given earlier. Those stars that are no longer main sequence stars are known as Post-main sequence stars. These stars burn helium and are at the end of their life span. After 5 billion years our Sun would also become a post-main sequence star before its eventual death.

Though there are so many other astronomical considerations, the above 12 items are the chief ones that need to be evaluated to find out the impact and influence of your Birth Star. 

Muthu Ashraff

Cosmic Adviser

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E-mail:    cosmicgems@gmail.com

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