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NGC 2420 anyone seen the twinkling comet in this cluster ?

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#1 Sky_LO

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Posted 15 March 2019 - 07:02 PM

Hello, I was observing a couple of nights ago and looking at open clusters.   The name of NGC 2420 caught my eye..."the twinkling comet" cluster. 

I added that to my target list for the night as it sounded interesting and I wondered what that was all about.   

 

The moon was up and fairly bright so I was only getting the brighter stars in this cluster....but then I saw what appeared to be a little fuzzy ball in the group....next to another star - almost looking like a fairly widely separated double star except the fuzzy "comet" was maybe 2 1/2 times as large as the nearby star.  

 

As I was looking at the fuzzy ball it faded right out to blank... and a few seconds later it was back.    I stared at this thing for almost ten minutes because "mind blown"  It just kept disappearing and reappearing every few seconds.   Not fast, but slowly.    I think I discovered the "twinkling comet" within this cluster.      

 

My research led me to a description of the "blinking nebula" which basically said it is sort of an optical illusion where by the star nearby  (or within - in the case of the blinking nebula)  is in just the right proximity to cause sort of a night vision blindness and the fainter object (or the nebula) blinks in and out as your eyes move while observing the object.          

 

I thought this was extremely cool.    Way fun.   I see a lot of astrophotography of this cluster, but I could not find any reference to the blinking comet or anyone talking about it, except for the name of the cluster itself.     I am pretty new at astronomy and observing so I had a few questions that I wanted to throw out there.....

 

1) Is the small fuzzy ball object actually a stationary comet?  (I thought comets moved)

2) If it is not a comet, what is it? ( a small globular?) 

3) Has anyone seen and experienced the 'twinkling comet' in this way?  

 

-Lauren     (viewed in 8 inch Dob, Bortle 4.5 sky,  50% moon out,  ES 14 82deg EP ) 


Edited by Sky_LO, 15 March 2019 - 08:23 PM.

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#2 clearwaterdave

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Posted 15 March 2019 - 07:36 PM

Very cool.,if the clouds part early enough I will check it out.,thanks



#3 Carol L

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Posted 16 March 2019 - 12:28 AM

Hi Lauren, you're absolutely correct... comets move, so what you saw was definitely not a comet. Someone probably just nicknamed the open cluster because it might have reminded them of a comet.

 

Planetary Nebulae have a reputation of fading (blinking) when you look directly at them, but my Sky Tools program doesn't indicate a planetary nebula inside of NGC 2420. (If you want to see what an open cluster with a Planetary Nebula inside of it looks like though, check out M46 - it contains Planetary Nebula NGC 2438.)

 

Getting back to NGC 2420, maybe there's a slight nebulosity around one of the stars, causing it to look 'fuzzy' when you're not looking directly at it. When you look away from it though, it bloats and gets brighter. I'm guessing that as you observed this open cluster, your averted vision and direct vision kept falling on the fuzzy star, making it appear and disappear. 

 

Here's why it happens....
Our eyes contain cones and rods. The cones are in our central vision and are active when it's bright enough to see color. But as darkness approaches, the cones begin to shut down and the rods become active. They specialize in showing us contrast in our peripheral vision - possibly a throwback from primitive man's need to detect things creeping around in the darkness.  
In astronomy we use our peripheral vision, but we call it 'using averted vision'. That's because nebulous objects are best seen by averting our eyes from looking directly at an object in order to best detect it. 

 

Hope this helps, and welcome to CN! flowerred.gif


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#4 Dave Mitsky

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Posted 16 March 2019 - 12:41 AM

There are images of NGC 2420 posted at http://cs.astronomy....9min_5F00_1.jpg and https://www.cloudyni...50887-ngc-2420/


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#5 Steve OK

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Posted 16 March 2019 - 07:48 AM

There is NGC 6826 in Cygnus that is called the "blinking planetary".  The central star is visible with direct vision, but the surrounding nebula is "not".  When you look away, averted vision kicks in and the nebula is visible.  The effect is quite striking.  I could not find any reference that describes NGC 2420 as anything but an open cluster.

 

Steve


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#6 Steve OK

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Posted 16 March 2019 - 10:36 AM

OK, I did find a reference.  Stephen James O'Meara calls NGC 2420 "The Twinkling Comet" cluster in his book Deep-Sky Companions: The Secret Deep, Volume 4 He apparently "named" it based on his own observations.

 

Steve


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#7 Sky_LO

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Posted 16 March 2019 - 12:02 PM

I also found that reference.  He says (paraphrasing)  he was sweeping the sky searching for comets and found a "fuzzy snowball" inside this cluster that looked like a comet.    

 

-Lauren


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#8 Carol L

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Posted 17 March 2019 - 12:26 AM

Lauren sent me a Google Books screenshot of O'Meara's description of NGC 2420... now I understand what happened.

 

"...I saw a round cometary form enter the field. My heart stopped; the diffuse object looked so stunning against the mottled starlight in the field - like a fuzzy snowball."

 

The fuzzy snowball wasn't 'inside' the cluster - - it WAS the cluster as he saw it drift into his eyepiece's field of view, against the background starfield. 

 

"But on closer inspection, I saw the "comet's vapors" twinkling with averted vision. When I increased the magnification, the "vapor" shattered into a myriad of tiny scintillating gems."

 

NGC 2420 reportedly has nearly a thousand stars ranging in magnitude from 11 to 18. Sometimes the dim stars in these rich (densely populated) open clusters are spread out evenly, and can be detected with averted vision as a background glow. But they can also group together in knots and chains.

Lauren, I think that's what you saw... a small knot of background stars that were bright enough to be seen with averted vision, but dim enough to vanish when you looked directly at them.

 

Thanks for bringing our attention to this cluster... can't wait to take a look. smile.gif


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#9 Sky_LO

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Posted 17 March 2019 - 01:36 PM

Carol, I think you are totally correct in your interpretation of the reference, he says the snowball spit into gems....the gems being the cluster.  

 

The twinkling comet cluster Stellarium says is about 7 minutes in size.....The object I saw was only about 10 seconds in size -

(I have seen the blue snowball nebula before - for comparison its size is about 12 seconds.)   I have observed about half of the M objects and over 100 objects in my first six months in this hobby.  

 

Definitely will have to search and look again !!  Maybe get some more magnification on it to see if it is a small grouping of dim stars.

 

I am feeling like my next astronomy purchase should be a detailed atlas / star maps.   It definitely looked like a small round galaxy or nebula.   Are objects sometimes uncharted - or not listed in Stellarium or SN7? 

 

The most likely thing is I probably missed the cluster due to the moon light pollution and found something else entirely - a mystery object ? - very nearby.  

 

I love this astronomy stuff - and I am learning as I go !!    Fun!

 

-Lauren


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#10 Carol L

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Posted 17 March 2019 - 09:12 PM

The handful of brighter stars in the cluster are in the 11th magnitude range - all others begin at 13.8 and go dimmer from there. Going back to the area is the only way you'll find out if you saw the cluster - or if, as you say, you found something else. Makes you feel like a super-sleuth, doesn't it? cool.gif

 

Because there are so many dim stars in the cluster, it might be best to re-visit it after the moonlight is out of the way. Remember, though - as you increase magnification, the exit pupil of your eyepiece will get smaller - and less light will reach your eye, making the dim stars even dimmer. Sometimes it's best not to increase magnification too much. LIke Ellie's Dad said in the movie 'Contact': "Small steps, Ellie, small steps."

 

When I went through the Herschel 400 lists (1 & 2) with my 8" SCT, I found that the faint galaxies were a LOT esier to see under medium magnification. Tapping the OTA (optical tube assembly) to make the target jiggle helped a lot too, because a moving object is easier to detect than a stationary one. You won't be looking for galaxies in this cluster, but you WILL be looking for a nebulosity - and the same rule applies.

 

All of my main observing equipment is unobtainable at present. My astro-shed is 200' behind the house, and has been snowed in for the last few months. The daytime temperatures have been above freezing lately though, and we're rapidly losing the snowpack. So as soon as I can take a peek at the cluster (16" Dob) I'll be sure to come back here to touch base.

 

flowerred.gif 


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#11 Sky_LO

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Posted 18 March 2019 - 07:14 PM

Dang, Carol you are an astronomy rock star !!!


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