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Puzzling Late-Night Observing Session

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#1 FirstSight


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Posted 06 December 2012 - 02:36 AM

Late last night (12/5-6) I got up around 4:30am for a rooftop-deck observing session down at the beach with my NP-101. The half-moon was up high by that time, but under clear skies the transparency and seeing were very good, and the air fairly dry for a marine environment. Among the objects that had me up at that hour was my first seasonal opportunity to gaze into the Canis Major/Puppis region, since down here I have nearly unobstructed horizons, especially to the south, whereas my southern view is too restricted at home in Raleigh for a good look into this region.

WHAT WAS PUZZLING is that using both a 21 Ethos and a 13 Ethos, I quickly and easily found M47, but could not find nearby M46 despite much effort. With no moon in the sky, I have repeatedly and easily found both clusters before by starhopping last winter from my rooftop deck observation spot with the NP101. The other puzzling aspect was that I saw Corvus and Spica up high enough already to the east to give M104 a try, and found it with only a couple of minutes effort, dim and small as it was at just 42x in the 13mm Ethos, not but a few degrees farther to the east side of the half-moon than M47 was to the west of it. I could also recognizably make out the Canis Major cluster (NGC 2362), although the half-moon was bright enough to wash out most of its jewel-like glory and some of its stars. To the north, Ursa Major had risen high enough to give me my first look at M81/M82 in several months. I also got a look at Saturn in my scope with a 4.7E rising over the ocean with Venus just clearing the horizon, but it was too low for more than a fairly "soft" view. In an earlier observing session that night, around 10pm I starhopped to Uranus, which is a bit tricky to pick out with a 17E used as my "finder" eyepiece, because at 32x its planetary disc is only incrementally distinguishable from the apparent size of brighter stars and its pale cream-tinged turquoise color isn't so immediately distinguishable from blue or paler yellow stars at that magnification. I was going to try for Neptune as well, but its position at that time was just far enough west that the needed guide stars to hop to it were becoming naked-eye obscured by the of the upper reaches of the Myrtle Beach light dome, and so I decided to leave that for another night.

Nevertheless, I'm STILL PUZZLED why M46, one of my favorite clusters in the whole celestial sky in any season, was so elusive, even with the half-moon in the sky, when it really wasn't all that tough to find M104.

#2 star drop

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Posted 06 December 2012 - 09:47 AM

M46 is about the same size as M47 but M46 is about two magnitudes fainter.

#3 lamplight



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Posted 06 December 2012 - 10:15 AM

i was surprised here to see it clear at around 11:30pm so i went out as i have been waiting to explore the very same region. i found m47 then m46 both for the very first time last night. i LOVE those faint , fine clusters like M46.. i only have a narrow field of view from my house to the south with a large obstruction of trees southeast , so i have to wait for things low in the south sky to crest them. for some reason i didnt know M81 was in the area.. ive got to see what that looks like from here.

obviously as a noob i dont know why you couldnt see it. i was using unpowered SCT with 6/6.3 focal reducer and 25MM ES 68*. i did find those two before the moon came up though.. i was on to M93 and M50 by the time the moon came up.. between that and under dressed and fingers getting close it was more of a race than pleasure.. i have to go back and do some reading on the clusters i found last night but a couple of hem were the faint and finely dotted like M46. beautiful.. better luck next time!

#4 JimMo


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Posted 06 December 2012 - 04:58 PM

I can usually see both in my 60 mm finder scope, but that's with no Moon. Just a guess but maybe you needed more power to see M46 with the Moon nearby?

#5 Achernar



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Posted 06 December 2012 - 06:49 PM

M-46 is much older than M-47, and as a result, it's member stars are a lot fainter than the ones in M-47. Perhaps your skies were milky in that region and that was why M-46 eluded you. I personally have no problem spotting it from my light polluted front yard as long as the skies are good. The stars are faint, but the planetary nebula NGC-2438 in front of it makes M-46 worth the effort to look at even from my city.


#6 Jon Isaacs

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Posted 08 December 2012 - 05:58 AM

WHAT WAS PUZZLING is that using both a 21 Ethos and a 13 Ethos, I quickly and easily found M47, but could not find nearby M46 despite much effort

M46 has essentially no bright stars so it is more difficult to spot. I suspect you could have spotted it using more magnification, a 13mm eyepiece in the NP-101 is about 41x with a 2.4mm exit pupil. Since M46 is a cluster consisting of individual stars and not an extended object, increasing the magnification will increase the contrast. I generally crank up the magnification when trying to spot M46 if the skies are bright.


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