楼上的同好太谦虚了，这个你肯定看过！
偶最爱的疏散星团是M45，第一楼里说过了。
但是最过瘾的，要算CR70，全天最亮的疏散星团之一，一个小双筒基本上能放的下的。
都说M45亮，但是七姐妹的星等“才”1.2，CR70可是和大熊的北斗七星一样，都是0.4！
亮度差2倍吧……
在偶的7*30小双筒里面看——满眼尽是蓝色白色，大小不一的星星，极其养眼。
讲了半天“CR”是啥？平时见的一般都是“M”。“NGC”啊？
这里讲一下CR的含义，据摇光版主介绍：这是瑞典天文学家Per Collinder在1931年编的一份疏散星团的星表，收录了471个疏散星团。用Cr简称。
那CR70是什么东东？
说出来可能不少人会很郁闷——它的“代言人”是猎户三星！
于是，一地眼镜……
不绕弯子了，切入主题吧——猎户腰带上的CR70！
先道个歉：E文功底不佳，无法达到林纾先生所讲之标准“信、达、雅”，这里就贴一下英文的说明，甚憾！
但是文章不是很难，大致的东西还是可以了解的。
Collinder 70, a big open cluster incl. Orions Belt
The winter constellation of Orion holds many treasures for deep sky
observers, some of them among the best you can find in the night sky.
But there is one object that most observers have “seen”, yet few are
aware of its existence. The name of the object is Collinder 70, a large
open cluster, located around the belt of Orion. Collinder 70 includes
all three belt stars: Mintaka (the Girdle), Alnilam (The string of
Pearls) and Alnitak (the Belt). The cluster has a diameter of almost 3
degrees and consists of 100 stars or more. Most of them are of the 10th
magnitude or brighter.
This is an object for binoculars! In a telescope you would only see a
part of this magnificent deep sky object. On a clear and moonless
night, seeing Collinder 70 with all it’s stars grouped around the
three bright belt stars, will give you the same WOW experience as
looking at the Pleiades or the Alpha Persei cluster for the first time.
When observing, take your time. Follow the beautiful chains of stars.
If you have 10x binoculars or more, look for some double or multiple's.
Try to split the A and C component of Mintaka (Delta Orionis), the star
at the western end of Orion’s belt. Mintaka is an eclipsing binary
with a period of 5.7 days. The 6.7 magnitude C component is separated
by 52.6” from the A component in position angle 359 degrees.
Find the 6th magnitude E component of the multiple star system Sigma
Orionis, separated by 41.60” from the A component, in position angle
61 degrees. You can find Sigma Orionis just a degree southwest of Zeta
Orionis (Alnitak), the easternmost of the belt stars. Look closely and
see if you can find some stars that differ in color. Maybe you should
try to make a sketch of the cluster. Whatever you do, enjoy it!
On the first image below you see an overview of the constellation
Orion, the red circle representing the field of view (FOV) of 3.5
degrees binoculars centered on Collinder 70. As you can see, you
definitely need binoculars to see the whole cluster in the same FOV.
Binoculars with a 5 or 6-degree FOV are better. They show Collinder 70
nicely framed in its surroundings. The second image should give you an
impression of Collinder 70, seen through binoculars with a FOV of again
3.5 degrees.
说明来源：
www.backyard-astro.com/deepsky/bino/02_b.html
图片来源：
http://dvaa.org/AData/images/Cr70.jpg
http://www.masil-astro-imaging.com/FTP/Orions%20belt-2.jpg
http://www.boonhill.net/NCO/members_pictures/Kessler/beltsmi.jpg
http://www.schursastrophotography.com/images/schmidt2/Belt2F800.jpg
antwrp.gsfc.nasa.gov/apod/ap030207.html
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本帖最后由 Eldghost 于 2007-1-28 03:52 编辑 ]
