A bright, white triangular object appeared in the sky above tree line moving in a horizontal trajectory then disappeared quickly.

I was standing with my husband on the deck of our mountain-side home in the White Mountains of northern New Hampshire looking at the sky without a telescope when an extremely bright, white object suddenly appeared in the sky above tree line and moved horizontally. As weather allows, we typically look at the stars (truly little ambient light) and are accustomed to the relative size, height, and movements of airplanes, satellites, comets, and meteor showers. This object was quite different in shape, size, brightness, and movement. It appeared much lower on the horizon than naturally occurring celestial objects, airplanes, or satellites. It appeared quite suddenly as a bright, white triangular shape with curved edges, rather than a typical sharp point of a triangle. It was much lower in the sky than any moving object I have ever seen. I observed it moving at rapid speed horizontally for 30 seconds without emitting any sound. My husband looked in this northeast direction in time to see the object moving for approximately 10 seconds before it disappeared. The disappearance was quite odd, as it appeared to “turn” as though making an angular turn before it disappeared below tree line from our vantage point.