The cave filled with mosquitoes as soon as the sun set. But despite the bites, the darkness, the cool isolation and the stories he'd heard of terrifying Australian wildlife, the Polish-born Zajac was too fascinated to be scared.

He looked through his camera lens. Hours passed. Then, there it was - clearer than it could ever be when seen with the naked eye: the bedazzled core of the Milky Way.

It was April 2019. Zajac, a Silicon Valley software engineer and hobbyist photographer was visiting Sydney for work when he caught the train to Kiama in search of this moment.

He captured the Milky Way sprawled over the Cathedral Rocks, framed by the buzzing cave, with Jupiter - the brightest thing of all - putting in a surprise appearance to the left of frame.

The resulting picture, titled Galactic Portal, is a finalist in Royal Museum Greenwich's Astronomy Photographer of the Year awards.

"It was a cool and mostly clear night, but later in the night a very thin layer of clouds came out luckily not covering the stars, but giving them a glowy look you can see in the photo," recalls Zajac, 32.

"One of my favourite types of images are nightscapes which include the Milky Way as a prominent part of a landscape.

"It's exhilarating to see the Milky Way arching overhead in a dark location and I find it to be a fascinating subject to capture, especially because modern camera sensors can 'see' much more than our eyes."

The nomination is the second in as many years for Zajac, who shares his pictures on Instagram here.

The competition winners will be announced on September 10.