My new budding passion is 'astronomy' in the widest sense. I've always been intruiged by the night sky, and finally have the minimal tools necessary to try and capture some of its beauty. As yet, my minimalist toolset consists of: a Canon Eos 70D, a fast UWA (Tokina 11-16mm f/2.8), a fast medium length zoomlens (Sigma 50-150mm f/2.8), a decent tripod, an intervalometer, and the freeware programs DeepSkyStacker and RegiStax. The lack of a tracking mount and telescope means results so far are not mightily impressive... Until I have those, I enjoy the challenge of shooting 'bright wide-field' objects, hone my postprocessing skills, and most of all: enjoy the time spent gazing at the stars!
I checked your galleries (very nice pictures of your home country!) and with your D800 photographing the night sky should be no problem at all. If you have a wide fast lens (let's say 35mm or wider and f/2.8 or faster) and a sturdy tripod, you're good to go. Ireland has some nice dark skies:http://darksitefinder.com/maps/world.html (green is ok-ish, blue is very good, grey/black is better than I've ever had!)
Here's a resource that will help get you started:http://www.astropix.com/html/i_astrop/toc_ap.html (geared towards "deep space object" imaging - capturing the Milky Way over a landscape with a wide-angle lens is much easier)
If you have specific questions, I can advice the Astrophotography forum at DPR: https://www.dpreview.com/forums/1059