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Binocular Icon 52: The Alpha Persei Moving Group.

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#1 rodelaet

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Posted 01 February 2009 - 01:50 PM

Melotte 20

On a clear winter night, a small patch of light can be associated with Alpha (Mirfak) and Delta Persei. This brightening of the Milky Way can be seen with the naked eye. A pair of binoculars will reveal an interesting star field between Alpha and Delta Persei. This group of stars is also called the Per OB3 association or the Alpha Persei Moving Group. It was catalogued in 1915 by the British astronomer Philibert Jacques Melotte as the 20th entry in his catalogue of open star clusters. Mel 20 is a large and bright object. At a distance of 540 l-y, it is not much farther away than the Pleiades. Its size of almost 4° makes it the perfect binocular object, even for light polluted skies. I observed Mel 20 with the first quarter moon nearby. Melotte 20 reminds me of a snake, Alpha Persei being the head and Delta the tail. The sketch shows only the core of the cluster. A total of 100 stars are believed to be true group members. Many outlying members of the group are just too spread out to be seen in a single field of view.


Site : Bekkevoort, Belgium ( 51° N )
Date : December 7, 2008
Time : around 20.45UT
Binoculars : Bresser Spezial-Jagd 8x56
FOV: 5.9°
Filter : none
Mount : Trico Machine Sky Window
Seeing : 3/5
Transp. : 3/5
Sky brightness : 18.98 magnitudes per square arc second near zenith (SQM reading).
Nelm: 4.8
Sketch Orientation: N up, W right.
Digital sketch made with Corel Paint Shop Pro X2, based on a raw pencil sketch.

(Note: if the sketch does look too dark on your monitor, try to darken the room.)

Attached Files



#2 varmint

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Posted 01 February 2009 - 01:56 PM

Thank you for sharing. I also like the historical perspective. Where do you get that sort of information?

Also, I really like how you have shown a very faint light cone/halo around the brighter stars. Though this is from a binocular, I see this type of behavior with my telescope. I used to attribute it to moisture/dew forming on my optics (either objective or EP), but have seen it much fainter a few times over the past month when no dew is present.

Thanks for sharing.

#3 rodelaet

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Posted 01 February 2009 - 02:35 PM

Thank you, Jim.

The background information on deep-sky objects can be googled or yahoo-ed. Amazing how much information is available today.
Add to that my growing collection of books. :tonofbricks:

About the glare : This is how I see the eyepiece view. I wear glasses while observing. A small amount of glare is present around brighter objects in my world. It is also a convenient trick; it helps to tell my 'audience' : this is a bright object, cause your monitor can not show the dynamic range visible in the eyepiece. Your eyes will translate the glare into 'brightness'. :)

#4 frank5817

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Posted 01 February 2009 - 07:16 PM

Rony,

Thia is a most impressive sketch of Mel 20. I can no longer look at this region of the sky without thinking back to comet Holmes. I still think these binocular sketches of yours are the greatest and you set them up with very good narrative too. Awesome work. :bow: :bow: :bow:

Frank :)

#5 CarlosEH

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Posted 01 February 2009 - 10:44 PM

Rony,

A beautiful and accurate observation and description of the Alpha Persei (Mirfak) region. Mirfak appears to glow in your observation. Thank you for sharing it with us all.

Carlos

#6 rodelaet

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Posted 02 February 2009 - 05:10 PM

Frank and Carlos,

Thank you for the comments.
I'm glad that you like the sketch. :)

#7 JayinUT

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Posted 02 February 2009 - 06:37 PM

Wow! Another one and please keep em coming. They are so wonderful. I'm not going to add anymore than what you've said but will agree that I go first to books for information that I include on my observation form and then to google if I want more (for example on NGC 1931 which I observed and sketched last night I need to google for more info on that). Great job again.

#8 Special Ed

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Posted 03 February 2009 - 10:28 AM


Thia is a most impressive sketch of Mel 20. I can no longer look at this region of the sky without thinking back to comet Holmes.


I agree with Frank about the sketch and about the comet. :) Mel 20 is a showpiece (as is this drawing) and when it grew a new "star", that just added to its luster. :cool:

#9 rodelaet

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Posted 03 February 2009 - 04:44 PM

Jay and Michael,

Thank you for the compliments!

#10 Tommy5

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Posted 03 February 2009 - 11:00 PM

Excellant sketch, even from the lp chicago suburbs i can see that this region is rich with stars with binoculars, thanks for posting, Frank is right about Perseus i always think of Holmes when i look at it, of course i also think of comet West of 1976 when i look at Altair, funny how our minds work.

#11 rodelaet

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Posted 04 February 2009 - 03:17 PM

Jane,

Thanks!
I'm glad that you like the sketch. :)

#12 Vincent Becker

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Posted 05 February 2009 - 04:31 AM

Excellent sketch indeed, I'll try to spot this cluster with my binoculars.

As for the glare seen around bright objects, it can be some diffusion in the optics but also the diffraction pattern wich is easier to see around bright objects.

#13 GlennLeDrew

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Posted 07 February 2009 - 04:11 PM

About glare and spikes around bright objects... one's own eyes do most of that.

It's worth pointing out the following:

- Mirfak (alpha Per) is a member, it being an evolved yellow supergiant. Depending on its mass, it just might blast off as the final supernova of this 50 million year old cluster. Most certainly several previous supernovae have already gone off here. At least two runaway stars are currently flying away from Mel 20, having been released after their massive binary companions suddenly lost a lot of mass.

- Mel 20 is the core of the very extended Cas-Tau OB association, whose members are spread over some 100 deg. of sky between Cassiopeia and Orion.

- And the Cas-Tau association is near the center of the 4,000 by 2,000 l-y wide Gould Belt. It's likely among the first generation of stars to form in this expanding ring which is even today minting new stars in a number of young associations around its periphery.

#14 rodelaet

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Posted 08 February 2009 - 03:54 PM

Vincent,

Thanks for the compliments.


Glenn,

Thanks you for the additional information. I appreciate it very much. :)






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