temporary light on the eastern horizon that precedes the rising sun by about an hour; also called zodiacal light
Most comics historians date the dawn of the Silver Age to the Sept-Oct 1956 and the appearance of Showcase #4, with the first Barry Allen Flash. Others will argue for November 1955 and Detective #225, featuring the introduction of Barry's JLA partner, the Martian Manhunter. As you know, I just use 1955 in general because of the appearance of the Comics Code Authority Seal on the covers, starting in around March of that year.
But if we were to date it from the resurgence of the superhero genre, which is certainly one of the hallmarks of the Silver Age, it's amazing how complicated things get, because there were a lot of efforts at relaunching old superheros and inaugurating new ones in the 1954-55 era. And despite Showcase #4 supposedly coming like a bolt from the blue, it took three more years before Flash graduated to his own magazine, and before DC attempted to bring back another updated Golden Age hero (Green Lantern).
For example, Sterling published four issues of a superhero named Captain Flash starting in November 1954. But before that, Headline Publications put out seven issues of Fighting American, a Simon & Kirby collaboration, with the first issue bearing an April-May 1954 cover date. Here's the cover to #2:
And earlier still, in December 1953 Marvel (then known as Atlas) tried bringing back the Human Torch, Sub-Mariner and Captain America, with five issues of Young Men:
In February 1955, Charlton attempted to bring back the Blue Beetle, although in this case it was simply a reprint title: