Michael A. Covington    Michael A. Covington, Ph.D.
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Ichthys

Daily Notebook

Popular topics on this page:
McNeil's Nebula has disappeared
Astrophotos:
Pleiades
M31 (Andromeda Galaxy)
Veil Nebula
NGC 281 (Pac-Man Nebula)
M33 (Triangulum Galaxy)
M78 and McNeil's Nebula
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2018
November
12

McNeil's Nebula has disappeared

A bulletin from the British Astronomical Association informs me that McNeil's Nebula, a faint nebula in the field of M78, has disappeared from view and, as of November 6, could not be imaged with telescopes as large as 610 mm (24 inches).

This is of course a variable nebula, one illuminated by a star whose brightness fluctuates. In the pictures below, you can see that I successfully photographed it with my 8-inch in 2016, but two nights ago, my 6.5-cm (2.6-inch) couldn't get it, which doesn't prove it is all that faint; I want to go at it again with the 8-inch telescope soon.

Picture

Picture

The first picture is a stack of fifteen 1-minute exposures with a Celestron 8 EdgeHD at f/7 and a Canon 60Da at ISO 800. The second is a stack of seven 3-minute exposures with an AT65EDQ refractor (6.5-cm f/6.5) and a Nikon D5300 at ISO 200.

2018
November
11

Armistice

Today, on Veterans' Day, which this year is also the centenary of the end of the Great War, I want to thank everyone who risked or lost their life in defense of their country.

As best I can make out, World War I was a brawl that started with no noble cause and, like most brawls, ended with everyone fighting in self-defense. One thing that emerged from it was the new concept of preventing war, not by giving in to those who want to pillage you, but by preventing misunderstandings and heading off conflicts of interest.

I am happy to be involved today in defense research that aims to prevent war. And I am thankful that my freedom today was earned by so many who risked, and in some cases suffered, death in order to defend it.

2018
November
9

You need spudgers!

Picture

A spudger is a 21st-century tool that I don't know how we ever did without. It's a plastic prying tool for popping open plastic enclosures without scratching them, getting batteries out of holders, and a myriad other uses. I recommend this set of 20 for $8.99 from Amazon. It's a round chisel on one end and a straight chisel on the other end, with a hook whose exact purpose I have not yet divined. Put a couple of spudgers in every pencil cup. You'll use them constantly.



Through Nikon eyes

For comparison to last month's tryout of my Nikon 180-mm lens with a Canon 60Da, I have also tested it with my Nikon D5300. The D5300 has an inherently higher-quality sensor than the Canon but is less sensitive to the deep-red light of hydrogen nebulae. But it does see nebulae reasonably well, especially the blue hydrogen-beta emission, so that nebulae we thought of as red come out purplish or blue.

Here's the Veil Nebula, a high-temperature supernova remnant with lots of hydrogen-beta:

Picture

Here's the "Pac-Man nebula," NGC 281, which I haven't photographed before:

Picture

And here's the galaxy M33, which I've photographed many times, but I was surprised to get such a good view in town:

Picture

Each is a stack of ten 2-minute exposures at ISO 200, 180-mm lens at f/4.

2018
November
8

43 years

Today marks 43 years since Melody and I met. I've told the story of our meeting several times in the Daily Notebook. 4300 more years would not be enough!



Short notes on recent events

My new book, Digital SLR Astrophotography (2nd ed.), hasn't even made it to North America yet, but I've written plenty of updates and additional notes, which will interest you even if you don't have the book. Enjoy!

On Saturday I went to the Stone Mountain Hamfest and found it still diminishing, roughly half the size it was when I first attended it in 1988, or a little less than half, but still worthwhile. I bought a cigar box full of IF transformers, one of which will supply a replacement for my Hallicrafters receiver. And a few fuse holders. And nothing else. Nowadays eBay and Amazon give us an efficient market for everything.

We've just had an election, which threatened to include the spectacle of Georgia's chief election official, Secretary of State Brian Kemp, certifying that he, candidate Brian Kemp, had been elected governor by a 50.3% majority. At least he has had the good sense to resign prior to doing the certification. No reflection on his personal honesty, but I don't think the person who runs the elections should be eligible to be a candidate for any office except re-election to his own.

Apart from that, I have nothing to say about politics. It is too much like football. People take sides for the sake of taking sides and despising the other side. Is anyone interested in solving problems rather than despising people?

More astrophotos tomorrow.

2018
November
4

More new dogs and old tricks

I know it seems I'm taking the same astronomical photographs over and over, but what I'm doing is a shakedown cruise, so to speak, of some new configurations of equipment that I want to be ready to take to Deerlick or other sites without further preparation. So I'm photographing familiar objects to make sure everything works well and I know the best settings.

Picture

Here you see the Pleiades, with interstellar dust. The "rig," as they would say in ham radio, is a Celestron AVX mount carrying a Nikon 180-mm f/2.8 ED AI lens from days of yore, set to f/4, with a Nikon D5300 camera body. This is a stack of ten 2-minute exposures at ISO 200 without guiding corrections.

The catch is, some time during the observing session, after I had taken flat fields and some of the pictures, a dust mote got on the sensor. So the pictures from this run are going to be cropped fairly tightly to exclude the dust mote. Stand by for more.



Pushing an iOptron SkyTracker to its limits

I've told you about my iOptron SkyTracker before; it's a portable tracking mount for a camera. But how well does it track the sky?

I've been testing it and have found that its total periodic gear error is 80 arc-seconds (a bit much, considering the high quality construction; iOptron says it's at the high end of their range but not actually defective). That results in a maximum error (discrepancy between desired and actual motion) of about 25 arc-seconds per minute of time; often less.

And that is quite tolerable. I find I can get good 30-second exposures with a 200-mm lens, where each pixel is about 4.5 arc-seconds.

Picture

Picture

Here's a stack of 13 30-second exposures of the Andromeda Galaxy (M31) with a Zuiko 200-mm f/5 lens (the one I wrote about last month) and a Canon 60Da. The enlargement shows the picture at full resolution so you can see that the tracking is satisfactory. Of course, the images were stacked using an algorithm that discards outliers, so brief tracking errors have no effect.


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