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# Thoughts on relative magnitude?

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I've been pondering this whilst driving to work this morning (I know how to have a good time !)

If you look through a scope at a star, let's pick hypothetical 'Star A', apparent magnitude 10, and using a scope of 5" aperture, and I wanted it to look 2 magnitudes brighter, which I believe is 6.25x brighter, would I need an aperture of square root of (5x5x6.25)? Which I think gives 12.5",ALL THINGS BEING EQUAL?

Would Star A look like a star with apparent magnitude of 8, COMPARED WITH what its brightness looked like in the 5"?

I know there are definitions for magnitude, but this is more a question of what people actually feel the increase seems like

Thanks

Mark

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57 minutes ago, markclaire50 said:

Would Star A look like a star with apparent magnitude of 8, COMPARED WITH what its brightness looked like in the 5"?

Yes. A scope with 2x the diameter gets 4x as much light. A scope with 1.4x the diameter lets in 2x the light. A scope having 1.6x the diameter increases the light by one magnitude, and a scope possessing 2.5x the diameter yields a two magnitude gain.

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3 minutes ago, Ben the Ignorant said:

Yes. A scope with 2x the diameter gets 4x as much light. A scope with 1.4x the diameter lets in 2x the light. A scope having 1.6x the diameter increases the light by one magnitude, and a scope possessing 2.5x the diameter yields a two magnitude gain.

Thanks Ben.

Confirms my thinking.

Mark

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As an added thought on this, I welcome thoughts on how much extra brightness (expressed as fractions of magnitude or whole magnitude) would be needed to make a borderline visible star into an obvious visible star. Assume a dark sky in one case and light polluted sky in another.

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One thing that can make a borderline star turn into an obvious one is altitude in the sky. At lower altitudes stars (and other objects) are dimmed through the effects of viewing obliquely through the atmosphere. Stellarium has a go at estimating this effect (atmospheric extinction) when it shows the data on a target. It can make quite a difference.

So planning to view a particularly challenging target when it is at it's highest altitude in the sky makes sense.

Not quite the question you asked though, sorry.

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22 minutes ago, John said:

One thing that can make a borderline star turn into an obvious one is altitude in the sky. At lower altitudes stars (and other objects) are dimmed through the effects of viewing obliquely through the atmosphere. Stellarium has a go at estimating this effect (atmospheric extinction) when it shows the data on a target. It can make quite a difference.

So planning to view a particularly challenging target when it is at it's highest altitude in the sky makes sense.

Not quite the question you asked though, sorry.

Still an interesting comment. Thanks John.

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1 hour ago, markclaire50 said:

As an added thought on this, I welcome thoughts on how much extra brightness (expressed as fractions of magnitude or whole magnitude) would be needed to make a borderline visible star into an obvious visible star. Assume a dark sky in one case and light polluted sky in another.

Increasing the focal length of a telescope has the effect of darkening the background. If the reason a star cannot be seen is because of sky brightness, it may not be necessary to increase the aperture at all. Just the focal length.
Obv. if the star is so faint it is below the level your eye can detect, then the only way to increase its brightness is with more aperture.

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I have found that applying high / very high magnification can help see faint point sources or move them from being averted vision to direct vision visible I'm thinking of targets such as the faint planetary moons of Neptune and Uranus.

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Very high (200x) magnification can help resolve stars in some globulars in my 102mm Mak.

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