Tri-Bahtinov Mask - First Light

While using a "normal" Bahtinov mask for a long time, I was wondering what about an upgrade and using a Tri-Bahtinov mask. 

I read about the use of a Tri-Bahtinov mask on the website from Joost Drogenberg. Using the Bathinov Mask Drawing Generator - https://satakagi.github.io/tribahtinovWebApps/Tri-Bahtinov.html - I was able to prepare one for my TAL200K f/8.5 telescope. A local company did the lasercutting work based on the svg file. 

This evening I did a comparison test  between both Bahtinov masks on the bright star Vega. With the normal Bahtinov, the centerline is good centered and thus in focus. Using the Tr-Bahtinov mask I get 6 groups of spikes each containing 3 lines. The principle is the same as before: make sure the centerline of each spike group is positioned in the center. According to some forums, the use of tri-bahtinov masks is made for Schmidt Cassegrain scopes to collimate for all axes. 

Upcoming Lectures Studium Generale Maastricht

Some interesting upcoming lectures @ Studium Generale Maastricht:

 

1) 13 okober 20h: Govert Schilling will talk about dark matter "the elephant in the universe". see this link

2) 29 september 20h: dr. Lennart de Groot will talk about earth magnetic field. see this link

Limb Darkening plot using ImageJ

 

Plotting the pixel intensity center to limb using software ImageJ (see link). I used picture of the Sun made earlier in feb 5, 2022 (OIII filter).

The use of ImageJ to make the plot is quit easy and accurate. 

Interesting Software: ImageJ, FIJI and AstroImageJ

I'm still reading about Stellar Astrophysics and more specific on the radiative transfer equation linked to limb darkening and in view of analysing images on exoplanets.

Some literature make reference to some interesting software called ImageJ (or FIJI is Just ImageJ). According to the website the software is able to display, edit, analyze, process, save and print 8-bit, 16-bit and 32-bit images. It can read many image formats including TIFF, GIF, JPEG, BMP, DICOM, FITS and "raw". It supports "stacks", a series of images that share a single window. It is multithreaded, so time-consuming operations such as image file reading can be performed in parallel with other operations.

It can calculate area and pixel value statistics of user-defined selections. It can measure distances and angles. It can create density histograms and line profile plots. It supports standard image processing functions such as contrast manipulation, sharpening, smoothing, edge detection and median filtering.

This is the link to the website for more information.

ImageJ is open source software with many plugin possibilities for astronomy. There is even a package called AstroImageJ - see this link.

Succesvolle Zonnekijkdag 2022

Op zondag 3 juli werd naar jaarlijkse gewoonte de zonnekijkdag georganiseerd. Sterrenvereeniging Helios Averbode was paraat aan Het Moment van de abdij van Averbode. Het werd een succesvolle editie, niet alleen door het weer maar ook door de vele bezoekers. Meer dan 130 geïnteresseerde bezoekers kregen de mogelijkheid om vragen te stellen aan de 10 aanwezige Helios leden en om de zon te observeren middels 6 opgestelde telescopen.

Lees het volledige verslag via deze link.

Meridian Line of the Milan "Duomo" Cathedral

On my way to Bologna and Firenze I stayed for three days in Milan. I visited the Duomo of Milan which is one of the biggest Cathedrals of the world. The Cathedral hosts the Duomo Sundial which was built in 1786 by the astronomers of Brera. The Sundial or Meridian Line measures theoretical 61,53m (horizontaly 55,07m and due to be blocked by the northern church's wall the meridian line ends vertical by 2,5m height). 

The sun light, is entering through a 25,2mm pinhole located at 23,8188m height in the church's ceiling. Due to the construction of the roof, the sun light only enteres the pinhole a 15min before and after it's heighest point in the sky.

Some interesting math about this Duomo Meridian line can be found via this website.

Other interesting data about the Duome Meridian line is available aswell via :

- https://www.divinamilano.it/la-meridiana-del-duomo-di-milano/

- https://eratostene.vialattea.net/meridianeaforo/milano/milanoduomo-2.html

Meridian Line of Basilica San Petronia in Bologna

When visiting Bologna I entered the Basilica San Petronia and remembered a presentation by Patrick from Helios on the famous meridian line.

One of the largest meridian line is located in this Basilica San Petronia in Bologna (Italy). It was constructed by (Gian Dominica) Cassini and the meridian line measures 66,8m. The sun light, is entering through a 27,07mm pinhole located at 27,07m height in the church's wall.

The meridian line was constructed to continue checking the dates of the Gregorian calendar, but Cassini also used it to verify Kepler’s second law by observing if the apparent diameter of the Sun decreased in the same way as its apparent speed. Cassini could thus observe the diameter variations of the Sun image which were projected on the floor of the church with the incredible precision and derive from them the variations of the Earth to Sun distance. He verified also that the Sun diameter (and hence its distance) did not decrease in the same way as its speed decreased: the Sun velocity variations during the year proved that the Earth was faster when it was closer to the Sun and slower when it was further away. That was the first observational confirmation of Kepler’s second law proving that celestial bodies were not uniformly moving along circular orbits as astronomers had believed and tried to describe for over twenty centuries. Moreover, Cassini’s measurements preceded of more than three decades the publication of Isaac Newton's Philosophiæ naturalis Principia Mathematica, which would have given a physical framework, the law of universal gravitation, to Kepler’s empirical relations, experimentally proved by Cassini with his meridian.

Even today Cassini's observations are used for scientifical studies eg.  analysis of Solar Diameter Measurements Made at the Basilica of San Petronio during and after the Maunder Minimum (The Astrophysical Journal, 912:122 (6pp), 2021 May 10)