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2025-11-13 - Sun

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Published: 25 November 2025

At this time of year, I only have limited opportunities to observe the Sun in White Light. This is due to trees, houses etc and a low sun that seems to collect clouds.

However, on this occasion I wanted to try out the 'G' band filter. I also wanted a record of AR 4274, the large group that was responsible for a number of 'X' classification Solar Flares. 

This was my first image with the new filter and to say that I was astounded would be a huge understatement. I really couldn't believe the level of detail that I could record with an 80mm refractor.

Note the tilt of the Sun, North is to the top-left of the image.

Equipment used:

• SvBony 80mm (ED) F7 refractor
• EQ5 mount with driven RA
• ZWO ASI 138MM Mono Camera
• Altair G Band Solar filter
• Baader Solar Film for Energy Rejection.

Processing was straightforward:

• SharpCap4.1 (500 frames)
• AutoStakkert! 4
• Registax 6 for wavelets and curves

 

 

 

 

A brief comparison between a SCF filter and a G band filter for Solar WL photography

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Published: 25 November 2025

Background

For many years, I have used a SCF (Solar Continuum Filter), produced by Baader for both visual and photographic observations of the sun. It has served me well, it is a green filter with a bandwidth of 7nm, centred on 540nm. It adds a nice level of contrast improvement and adds clarity when seeing is not as good as I would wish for. 

Take One Step forward

On the BAA Solar Section WhatsApp group, I noticed that some images were a magnitude better than mine, both in clarity, sharpness and the level of detail that was visible. Further investigation revealed that an Altair 'G' band filter was being used. This has a bandwidth of approximately 2nm at 430.3nm. This is in the blue end of the visible spectrum.

It was duly ordered from FLO and it arrived in early November. I screwed it into the rear of my 8mm Baader Hyperion eyepiece, the eyepiece that I usually use for visual observations of the sun. Unfortunately, the image was too dim to be of any use for visual observations but after attaching it to my ZWO ASI178MM mono camera. I could barely believe the difference in quality between the two filters.

Here are two images taken on 20251125, the first using the SCF for imaging:

This is not a bad image at all and normally, I would have been very happy with that. However, compare it with the following image, taken about 5 minutes earlier using the 'G' band filter:

Far more contrasty, plage and granulation convection cells are easily visible and the image appears to be much sharper.:

Both images were processed using:

• SharpCap 4.1 (Approximately 500 frames, best 50% stacked)
• AutoStakkert! 4 
• Registax for Wavelets and Curves

There is always a slight downside. The 'G' band filter needs an exposure about 10x longer than the SCF, about 100ms compared with 10ms. No digital gain was used.

Of course, the SCF will continue to be used for visual WL observations, but the G band filter looks like it will be a very useful addition to the armoury.

GMN - Global Meteor Network

Details

Published: 20 January 2026

Background

I am interested in most things astronomy related and this caught my attention a couple of (or perhaps more) years ago.  At the time, I thought it looked an expensive project and it went on the backburner for a little while. I really should have read the GMN WiKi a little more closely. In the scheme of things, this is really not an expensive project, especially when you consider the return and involvement in a true Global Citizen Science project.

What is it?

Broadly the system consists of a (very) low cost security camera with a very wide angle lens, LAN connected through to a Raspberry Pi 4 or 5 with an external internet connection to central data processing servers for the GMN, plus, for UK users, connection to the parallel UKMon (UK Meteor) infrastructure. I have assembled two camera systems - one pointing South West (identified as UK00DA) and the other pointing North West (identified as UK00DE).Their purpose is to detect and record meteor trails accurately enough, so that (with other remote systems) an accurate trajectory of the meteors original orbital path can be calculated. An additional and very important benefit is that any likely meteorite falls can be tracked and the meteorites recovered

The continuous (hours of darkness) image data collection from the camera is processed by the Pi identifying apparent meteor trails against a stellar background. There are two levels of data analysis, a quite intensive pre-upload processing phase that is carried out on the Pi. This involves eliminating anything that does not appear to be a meteor, for example aircraft trails, satellites. A meteor has a quite distinctive visual trail, it is normally very short duration, typically less than 2 seconds plus the visual cue of a trail that 'fades in' to maximum brightness then either terminates abruptly or "fades out" back to nothing. This contrasts with aircraft (usually flashing lights and a trail duration of many seconds) or satellites that may have a trail duration of several minutes. Once a valid trail has been captured, it is possible to backtrack this trail establish the meteor shower source or whether the meteor was sporadic.

The camera is set to have a fixed shutter speed. What this means is that each sequence  is formed from a set of frames of CMOS Camera rows and columns of data captured contiguously at a fixed timing. This allows the processor to determine the apparent velocity and direction of the trail against the stars that are captured within that sequence of frames. Frames are analysed in blocks of 10. Each frame is analysed, if there are insufficient stars visible (a minimum of 20 required for astrometry purposes) or no trail detected, the frame is nominally discarded.

Before you can start, the camera needs to be located, fixed and then prepared. There are 2 aspects of this, the first is very simple. From an image produced by the camera, simply create a mask, blacking out everything that isn't sky. The second task is to calibrate the direction that the camera is pointing. From an image previously captured on a clear night showing lots of stars, create a calibration file that fits matched stars to those on a downloaded star map. The process compensates for distortion  induced by the use of a very wide angle lens. This is a very worthwhile and enjoyable task

Walkthrough

This is a walkthrough of events that occurred on the night of the 2025 October 25-26.

A typical stacked image of all captured frames for that night looks something like this. You can see that the image is swamped by aircraft trails. 

This image is a stack of the 104 detected objects that were shortlisted as meteors. There are a few aircraft trails, but possibly, they just happened to be in frame at the same time that a meteor appeared.

After filtering, the image looks like this. Star trails can be seen as an arc of dots against the black sky background. Clearly, there are some aircraft visible but nothing resembling a satellite. This is a filtered image from all the objects detected that night:

Each trail is then compared against a map of background stars and its apparent velocity and position is calculated. The Pi then identifies the likely cosmic source and if possible, the 'parent' meteor shower source. 

This is a visual report of the meteors detected on the night of the 2025-10-25/26 with the source shower identified or the number and source of any sporadic meteors. 

The following day,  after the capture phase and initial processing has completed, the data is then uploaded to the central data processing servers and each potential meteor is compared with other cameras that may have detected the same trail The system has the capability to detect meteor trails up to about 300km distant and down to about magnitude 4. Aircraft and other flying objects that remained following the local processing phase are now eliminated as these fly much lower (usually less than 10km altitude) than meteors. Satellites orbit at a minimum altitude of about 160km and these are easily isolated and are now eliminated as accurate height information cannot be determined from a single camera.  Meteors burn and form trails somewhere between 75km and 120km altitude. The elimination phase is performed by triangulating the trajectory with 2 or more RMS systems pointing in the direction of the meteor.

The data is then processed and orbital parameters determined. This ongoing iterative process allows the real scientists to determine, with a great deal of accuracy, the source of the meteor and record this accordingly. The Global Meteor Network home page details how the data is captured and compiled.

the UKMon archive website has a search facility that enables a user to examine the meteors detected on any specific date (or date range). The data for my camera UK00DA for the night of 2025-10-25 provides this result.

Selecting the match for 2025-10-26 04:16 provides a detailed analysis for a particular meteor including (where the meteor was bright enough), the image that was captured by my own camera.

Captured moving from the SW to NE with Orion nicely framed.

Next stage in this project will be a 3rd camera pointing East. One for the spring.