Sunday, July 30, 2017

Back from the 2017 Nebraska Star Party

Ah, to be back in the land of 10,000 lakes and high dew points!

NSP 2017 is over, and it was a memorable one. Sunday (7/23) was clear and about as good a night as I've ever enjoyed at NSP--or anywhere, for that matter. The day had been in the low 90s, but the temperature dropped quickly as the sun set. There was a strong and gusty breeze that kept the mosquitoes away. (I realize big scope owners didn't like the wind, but I was imaging with a 200mm lens wildly overmounted on a CGEM.) The transparency was exceptional overhead; the Milky Way was nothing short of spectacular.  I don't think you could read by its light as one person predicted, but it was definitely casting a subtle, diffuse shadow.

I was able to collect some light frames of my current target, the Rho Ophiuchi Cloud Complex, then switch over to the Sadr area for the Butterfly:

The Rho frames have yet to be processed. The next night I decided to spend the entire night imaging the Veil:

What I like about this 200mm lens is how flat it is at f5.6, and free of vignetting.  There are two new things about these images:
  1. Instead of stopping down the lens with its internal iris I used a step down ring. This gets rid of the diffraction spikes caused by  the blades of the iris.
  2. I used PHD and BackyardEOS to dither the images.  It seemed to work very well!
The last night was cut short by clouds, so I only got five frames of the Rho area at 135mm:

As you can see, this lens has substantial vignetting.

By the way, 2017 NSP was on the hot side.  The Monday and Tuesday highs were 106 and 107 degrees, respectively. But it was the usual "dry heat" and both days had those great strong breezes.  I spent the afternoons sitting and reading semi-comfortably in the shade of the supper area canopy. Thank goodness NSP didn't happen the previous week when it had been both hot and humid.

Now it's on to eclipse planning and back to meteor counting!

Tuesday, July 18, 2017

Back To Imaging for a Bit; The Nebraska Star Party Nears

My wife got a new desktop computer after the 4th of July, and that translated into more than a week of transition from old computer to new. Because she didn't get a new monitor our ancient flat panel monitor was pressed into service so that she could run both computers at the same time. And because it was the monitor on my meteor-detecting computer, that activity was put on hold for the duration.

Luckily we just had a very nice run of third quarter moon clear nights. I was able to get out for two out of the three nights and tested the setup intended for the Nebraska Star Party. This year I'm not chasing any astronomical league program certificates so I'm keeping it simple: Big mount, DSLR, and short lenses.

From my second night out, here's an example:

It's the Lagoon and Trifid nebulae. This is a 200mm f/5.6 image based on only 10 4-minute light frames (ISO 800) and it gets reasonably deep.  This was taken at a light pollution yellow-green transition zone site; I'd like to try this again at NSP to see how much the difference in sky brightness affects the outcome.

Another target will be the Rho Ophiuci area and the dark lanes to its east. And, if there are enough clear hours, some of the dark nebulae that dot the area.  I may even try some super wide fields!

The weather at Valentine has been on the warm side, with some daily highs in the 100 to 105 degree range. The forecast for the first Sunday is much nicer at this point--A high of only 87, and a partly cloudy night with a pleasant low of 60. Monday's high is forecast to be only 88! It doesn't get much better than this.

The rest of this week is NSP preparation. No more imaging until then!

Sunday, July 2, 2017

Meteor Detection Using Argo

I should have posted some of the screen caps to show what Argo is capable of showing when using TV stations for meteor detection. These are from a session monitoring CHBX Channel 2 Sault Ste. Marie, Ontario broadcasting at 55.24MHz.

Here's one showing a couple of typical events. At left is an epsilon reflection from a meteor, while the slanted line at right is probably an aircraft flying at flight level somewhere near the midpoint of a line between my location in Minnesota and CHBX.

The next image is of an overdense reflection from what I assume was a larger meteor.

Most meteor reflections are faint and very short in time span (less than a second). The overdense and epsilon reflections are less common, and can come in a variety of forms--here's one:

I would like to catch a nice head reflection eventually.

Because Argo shows so many faint meteors, analyzing a series of screen caps will be interesting--and a lot of work.  I probably won't do much more with this until the Perseids, which fall conveniently between the Nebraska Star Party and the eclipse.

Saturday, July 1, 2017

Meteor Detection using National Weather Service weather stations

This is more of an update on what I've been doing since I got things working using TV station video carrier frequencies. Last time I was able to get what looked like a decent diurnal cycle out of a day's observation of Channel 2 (CHBX, Sault Ste. Marie, Ontario); before that I'd tried using regional weather service stations and been stymied by what looked like aircraft-created reflections. I live about 6 miles from Minneapolis-St. Paul International Airport (A Delta airline hub) and it has a lot of traffic.

Argo did so well at getting the most out of the TV data that I thought it worth trying with the weather stations.  It did not fail me.

Here is an 8 minute plot of activity at 162.475MHz:

It's a real mess, isn't it? Most if not all of that is air traffic. To see what it's telling us, let's start with a quieter time and add a little annotation:

The curved lines are reflections from aircraft arriving or departing the airport; the horizontal lines are the carriers from several weather stations. Note that they're slightly out of tune. The audio shift between them is roughly equal to the difference in the carrier frequencies, so all four are within about 45Hz of each other, an error of one part in four million. The strongest two stations ("B" and "C") are probably Rochester MN and Spooner, WI.

Argo shows the reflections clearly. The first diagram contains not just curves like these but other lines that probably represent flyovers, diversions, and other course changes aircraft make near an airport. Unfortunately, none of them look like the things I was able to see with TV.

I'll let the system run overnight and hope that the signals don't saturate like they have in the past. Maybe I'll see some meteor signatures in the flight free early hours of morning?

If I don't, I'm going to have to question the usefulness of weather stations for meteor detection. Even with that negative result I'll probably take my setup to this year's Nebraska Star Party where the aviation activity is considerably less.


The Virgo Cluster mosaic is now half done:

This is all I'm going to get this year, but it's not bad for such a terrible spring.