This is the third installment of the article series I've started in observing the heavens. This third piece has proven to need a bit more consideration as galaxies, despite their true size, can be the most confounded to observe, so I've wanted to produce a piece that explains, encourages & fuels your quest to tackle these illusive denizens of the night sky.
~x.X.x~
Ok, you've settled in for a night of observing. You have your list of galaxies that you want to nail. The charts, books and apps all tell you these are all bright suckers that are well within your scope's light grasp. Sky is clear, no Moon about, and the scope is primed...
But hang on! Where are they?
How come I can't see them, or they are sooooo underwhelming?
Where are their arms?
Is my scope a lemon???
Have I been conned?...
The galaxies are there. So are there arms, and your scope is not a lemon. BUT yes, there is a little bit of a con going on. And it isn't a deliberate one, but one born out of misinformation and ignorance. I too fell for this, and it took me MANY years to figure out what was going on.
The quasi con explained.
Here's the root of the problem. It starts with the "visual magnitude" that charts, books and apps all display. A galaxy is described as say 'magnitude 3'. It should EASILY be visible in your scope, heck even to your naked eyes. But you cannot see it naked eye, and you are barely able to make out a mere soft brightening in the field of view of the eyepiece.
The problem lies in how & what the visual magnitude actually means! Stars are listed with their magnitude, and stars are a point source of light. And this is how the magnitude of a galaxy is described - as
the entire light of the galaxy is put into a single point source! The kicker is that a galaxy is not a point source, but an extended object - it is spread out and has a size/dimensions. So the point source magnitude value is actually spread out across the entire dimensional space/size of the galaxy! That magnitude 3 galaxy you were trying to see has its light spread out over the same size occupied by four full moons!
This is the case not just for galaxies, but for all deep sky object, nebulae, open clusters, globular clusters, etc.
Take the Large Magellanic Cloud. It's visual magnitude is something around magnitude 0, a 'bright' sucker, as bright as Alpha Centauri! It
"should" be as easy to spot as Alpha Centauri even from light polluted skies. But it is difficult if not impossible to see the LMC from under light polluted skies, even though Alpha Centauri is easy to see. And under a dark sky it glows with a soft light. Remember, the LMC is huge in the sky, occupying a whopping 87 square° - the Moon's size by comparison is just 0.2 square°.
So, that brilliant magnitude 0 glow is spread out over a huge area, and unevenly too.
This is the case with all galaxies.
,
,
,
Situation explained.
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In the next post, I'll give you some tips on how to best observe galaxies, what you can see in them, and why their arms are most difficult to see - alas this last part needs the use of BIG aperture...
HOWEVER, even with small apertures if you know a trick or two, you will be able to spot a lot more galaxies than you may have until now...
Alex.