A friend of mine tends to ask crazy question about everything. Today he ask me what is the brightest star that is visible on both the hemisphere and in particular from Italy and Argentina. I tried to ask wolframalpha but nothing came up. Thanks in advance.
Sirius is the brightest star in the sky (excluding the Sun, of course), with a visual apparent magnitude of −1.46, and is visible to everyone in both Argentina and Italy, depending on the season.
In fact, Sirius is visible from anywhere in the Southern Hemisphere, including all of Argentina (which, I might add, is an enormous country stretching from just above the Tropic of Capricorn, all the way south to the Drake Passage separating Tierra del Fuego from Antarctica).
Sirius doesn't rise above the horizon for locations in the Northern Hemisphere north of 73°, but this is well beyond the northernmost point of mainland Europe at around 71°N, so Sirius is visible in all of continental Europe. As the northernmost location in Italy is around 47°N, Sirius at its zenith appears well above the horizon to anyone in Italy.