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Palomar

Member

From: USA

Registered: 2002-05-30

Posts: 9,734

Re: Star Magnitude

*I've not yet been able to discover why star (and other astronomical) magnitude is designated as it is.  For example, the sun's magnitude is -27.  The full moon's is -15.  The magnitude of the dimmest stars viewable to the naked eye is +6.

I've understood since a child that this is -how- star (and other astronomical) magnitude is designated.  When I first learned of this, around age 9, in a little astronomy book my parents bought for me, I was stumped as to -why-.  I re-read that section of the book at least half a dozen times, I fished through astronomy books at the public library seeking an answer, and later in my issues of "Sky & Telescope" magazine, seeking an answer as to why magnitude was designated in this fashion.

As a child, it seemed very strange that the brighter a celestial object is the higher in the negative it is classed, and vice versa that the dimmer a celestial object is the higher in the positive it is classed.  This puzzled me, because I associated brighter with hotter and colder with dimmer (as in the Fahrenheit temperature scale).  As an adult, I still find it strange.

So I'm still wondering:  *WHY* are star (and other astronomical) magnitudes designated this way?  I've not yet encountered an explanation. 

Can anyone offer an answer?

--Cindy

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We all know [i]those[/i] Venusians: Doing their hair in shock waves, smoking electrical coronas, wearing Van Allen belts and resting their tiny elbows on a Geiger counter...

--John Sladek (The New Apocrypha)

Euler

Member

From: Corvallis, OR

Registered: 2003-02-06

Posts: 922

Re: Star Magnitude

The magnitude system started with the ancient Greeks.  They divided stars into groups based on brightness.  The brightest stars were called stars of the first magnitude, the next brightest were of the second magnitude, etc.  The dimmest visible stars were of the sixth magnitude.  Eventually this system of star grouping was turned into scale to measure the brightness of any object.  Since the sun, the moon, and some of the planets are brighter than any star, they logically acquired a negative magnitude.

Palomar

Member

From: USA

Registered: 2002-05-30

Posts: 9,734

Re: Star Magnitude

The magnitude system started with the ancient Greeks.  They divided stars into groups based on brightness.  The brightest stars were called stars of the first magnitude, the next brightest were of the second magnitude, etc.  The dimmest visible stars were of the sixth magnitude.  Eventually this system of star grouping was turned into scale to measure the brightness of any object.  Since the sun, the moon, and some of the planets are brighter than any star, they logically acquired a negative magnitude.

*Wow, Euler.    Thanks!  You've solved an old mystery of mine. 

I should have posted about this sooner.  This question has been with me for so long that I guess I've become used to it just "hanging there" in the back of my mind all these years...if that makes any sense at all.

--Cindy 

---

We all know [i]those[/i] Venusians: Doing their hair in shock waves, smoking electrical coronas, wearing Van Allen belts and resting their tiny elbows on a Geiger counter...

--John Sladek (The New Apocrypha)