Billions of stars, one successful {photograph}: the core of Andromeda

Exploring hydrogen: taking a look at H-alpha mild

H-alpha is a deep purple wavelength of sunshine emitted by hydrogen, the most typical factor within the Universe and a significant constructing block of stars and emissive nebulae (clouds of fuel and mud that emit their very own mild). 

Dr Ed Bloomer explains, “Different physical processes produce light at different wavelengths, so different filters can be used to create images revealing those activities, or the elements producing that light.” 

Weitang says, “Although we already had the LRGB data, we also wanted to highlight the H-alpha structures in this region.” 

He continues, “We tried several times to collect H-alpha data to reveal the rich details in the arms. At that time, the core did not attract my attention because of relatively lower resolution. But now, with a telescope capable of achieving the best detail, we decided to revisit the core – and finally obtained 23 hours of H-alpha data.” 

The photographers clarify why they did this: “By carefully isolating and processing the H-alpha channel, we were able to enhance the visibility of these ionised gas clouds, which trace ongoing star formation. 

“The contrast between these glowing regions and the surrounding dust lanes adds depth and dimension, offering a fresh perspective on this familiar galaxy.”   

 

Picking a color palette

Weitang explains the daring purple color palette: “The H-alpha spiral arms in the core were the most important feature we wanted to highlight, so we chose a striking colour that would stand out from the star field. At the same time, we also wanted to preserve the natural beauty of the star field.” 

“We presented the spiral H-alpha arms in a reddish tone, finally choosing a palette where the red includes hints of orange.” 

Dr Bloomer says: “The colouring is interesting. It’s not the usual colour palette, and the dominant red is powerful, but we [the judges] thought it was not uncomfortably so.” 

The remaining picture fulfilled all the workforce’s expectations, and extra. Weitang remembers: “At first, we were overwhelmed with excitement. Later, we calmed down and set the image aside for a few weeks. When we revisited the image after some time, we were still fully satisfied with the result. That’s when we knew it was ready to share.” 

 

Why was this picture chosen because the winner?

As for why this picture was worthy of the highest prize within the ZWO Astronomy Photographer of the Year 2025 competitors, Dr Bloomer says, “We [the judges] were struck immediately by the technical achievement of retaining so much detail so close to the core, so we knew it was worth some careful consideration.  

“We chatted quite a bit about the framing: it’s quite a close crop into the centre, but we also adored that the image had such a dramatic diagonal structure.” 

Dr Bloomer says every decide had their very own causes for selecting the picture because the winner. 

“To my mind, it’s a really striking image from afar but also contains enough detail to stand up to close scrutiny. In short, it took a lot of skill to capture the data at all, and good judgement to present it in such a cool way!” 

When the photographers discovered that they had gained the highest prize, Weitang says, “The excitement was beyond words! We are truly grateful to the ZWO Astronomy Photography of the Year competition. It brings us great joy to share the beauty of the Universe with everyone.”