Stellarium Web is a free online planetarium right in your browser. A realistic starry sky from your location on Earth, in real time.
Any star, planet, nebula, galaxy, or constellation can be found through the search bar. Click on an object — name, coordinates, brightness, distance. Constellation lines, equatorial grid, and deep-sky object markers are all available.
The best feature is time control. Fast-forward or rewind: watch how planets move over months, check when the next eclipse will be, or see where Jupiter was on the day you were born. Time accelerates to any speed.
The observation point can be changed to any city — see what the sky looks like right now from Tokyo or Reykjavik.
Stellarium Web is the browser version of the desktop app that has been a standard among amateur astronomers for over 20 years. The web version is lighter, but for a quick "what's in the sky tonight?" — perfect.