Yes, you can certainly tan through an open window, as it allows for direct and unobstructed exposure to the sun's ultraviolet (UV) radiation. When a window is open, both UVA and UVB rays reach your skin with the same intensity as they would outdoors. UVA rays are primarily responsible for tanning and long-term skin aging, while UVB rays are the main cause of sunburn and vitamin D synthesis. Standard window glass typically blocks most UVB rays but allows a significant portion of UVA rays to pass through, which is why you can still tan (albeit more slowly and without burning as easily) through a closed window. However, with the window open, the protective barrier is removed entirely. It is important to remember that even if you are indoors, prolonged exposure to direct sunlight through an open window carries the same risks of skin damage, premature aging, and increased skin cancer risk as being outside, so wearing sunscreen is still highly recommended for extended periods of indoor sun-gazing.