Over the next few nights, observers with low western horizons may be able to observe a triple conjunction between the planets Mercury and Jupiter and the bright star Regulus.

On Friday, August 7, the two planets and star will form an equilateral triangle, 1 degree on a side. Mercury will be on top, Regulus to the left, and Jupiter to the right.

Look for them with binoculars just after sunset. Jupiter will be in the middle and the brightest of the three, at magnitude –1.7. Mercury will be on the right at magnitude –0.7. Regulus will be the faintest of the three, on the left at magnitude +1.3.

Brightness in astronomy is measured on an upside-down scale where the faintest stars visible to the naked eye are magnitude 6, the brightest stars are around magnitude 0, and really bright objects like the sun, moon, and planets have negative magnitudes.

All three of these objects will be very bright, but will be masked by the brightness of the sky just after sunset. If you wait until the sky has darkened, they will probably be too low to observe.

Three nights later, on Monday, August 10, Mercury will have moved away to the left, but Regulus and Jupiter will have moved closer to each other, less than half a degree apart. This conjunction will be very hard to observe because of its low altitude.

This will probably be your last chance to observe Jupiter before it passes behind the Sun on August 26. Look for it in the morning sky in mid-September.