What was that flashing light in the sky?

I'm new to astronomy (1½ months) and I live in New Jersey. Last night, July 31st, I saw a bright planet (I assume Jupiter) in the southwestern sky, and just below it what looked like an airplane with a flashing red tail marker — but it never moved. When I got home I looked at both with my 70-millimeter telescope. Jupiter had three moons in a line, but the object below it looked like an LED attention-getter that stores sold in the 1970s, flashing in different colors. What was it?

Antares with constellation lines

Fiery Antares, one of the most magnificent double stars for large telescopes, dominates this picture of Scorpius and western Ophiuchus.
J. Mullaney

Newcomers send us more questions about flickering, starlike objects low in the sky than anything else. You start noticing these twinklers when you pay close attention to the night sky.

Your mystery object had to be the bright orange star Antares, which was then sparkling about 5° below Jupiter (see the all-sky star map in the center of our July issue). Atmospheric turbulence makes all stars scintillate, especially bright ones when they are very low.

— Roger Sinnott