Every way of spotting a target suffers from uncertainty. Most suffer from delays (satellite photo is X hours old), security issues (keep your spies alive), and political considerations (Ukrainians might want to feel that they are fighting and winning, not just acting as push-button-when-told minions of foreign powers).
Waiting to attack it until that could reliably be done with all-Ukrainian assets, all of which the Russians already knew about - that maximizes the number of checked boxes, eh?
- Ukraine performed the initial radar detection
- Ukraine asked the US to confirm it was the Moskva (the US did)
- Ukraine attacked with their own targeting data
(Then news articles clammed up about the US confirmation, and the Pentagon put out some carefully worded statements that tried to establish distance)Which sounds reasonable. Warships like the Moskva are strategic assets.
That lowers the bar for acceptable amount of help from the US before Russia escalates.
> Which sounds reasonable
If you don't know anything about radars, yes.
Manual guidance wouod allow you to shoot the missile in the direction of the located target, until you are close enough for the missile to lock on and have it hit using automatic guidance. No idea what was done during hat particular attack, but it sure was possible without radar sorcery.
Ukraine also had a Bayraktar drone flying around the ship area at that time. It could have picked up rough coordinates from that.
It's plausible that Ukraine was told where the ship was, launched the missiles in that direction and they acquired and targeted the ship autonomously when they got closer. Of course that's pretty risky as a gambit but the downside was a failed strike and the upside was a doomed capital ship.
One could go so far as to say that "using Russian blood" has historically been and currently is their military doctrine.