Thursday, December 14, 2017

Re post of last night's entry, with more information.

This is an image from November 18, 2016 of M110.

M110 from last post, image taken a year later.

Compare this one to the one from the last posting. What's the difference? The one from November of last year, is a much, much longer exposure plus combining exposures from 4 color bands, LRGB. LRGB, which is luminance, red, green, blue, were exposure times of 60L, 9R, 9G, 9B, so a total time of 60+9+9+9 = 87 minutes vs. 3L for the one from this year ( 3 minutes in L band). (What's the L band, really? It's basically a clear filter, except it doesn't allow infra red (IR) light through. That's important because the camera sensor will respond quite well to IR. This can throw off the focus, sense we mostly look for the greatest response of the chip, ie, most output, to help determine then focus is achieved.)
You can read about M110 in the post from November 20, 2016.


NGC 404
This image shows a very bright star called Mirach, which is the brightest star in the image, and a galaxy to the star's lower left, which is the “fuzz ball”. The fuzz ball is actually the intended target for this image and is NGC 404, which is also know as the Ghost of Mirach. NGC 404 is about 10 million light years away and is described as a lenticular or elliptical galaxy. The fuzz (nebulosity) around Mirach is a bit of a puzzle. Mirach is a bright star, about 2nd magnitude. Because it is so bright, the light from it fills the sensor receptors and then spills over to adjacent receptors (pixels, actually). So, instead of the star appearing round, it has a tail going off to the right, which is where the extra light has spilled. That much I understand. It's possible that a similar phenomena is the cause of the dark curved streaks, but I don't know.


NGC 891
NGC 891 is an edge-on galaxy that is about 30 million ly away. From side to side, it's about 100,000 ly across.


And now the 10 second images.

NGC 752

NGC 752 is an open cluster that's about 1300 ly away and contains about 100 stars.


NGC 7662
Nebula, Shells visible, but not central star

NGC 7662 aka the Blue Snowball Nebula is a dying star, much like M57, the Ring Nebula in Lyra. There is a central star that has shed some outer layers of gas. Images with greater resolution can show the central star. It's presence is hinted at here, showing a somewhat darker center than outer edges of the nebula. Distance is not know with any accuracy. Estimates range from 1800 ly to 5600 ly.

NGC 7686

NGC 7686 is an open cluster containing about 80 stars. I've found little information on this cluster, including no estimate of it's distance.

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