Tonight – June 10, 2016 – as soon as darkness falls, look for the waxing crescent moon in the western sky. That nearby bright “star” is actually the king planet Jupiter, the brightest starlike object in the evening sky. The fainter light on the other side of the moon on June 10 is Regulus, the brightest star in the constellation Leo the Lion.
There’s no way to mistake Regulus for Jupiter – or vice versa. Jupiter is by far the brighter object, outshining Regulus by some 20 times. That’s not to say that Jupiter is the more luminous of these two celestial lights. It’s not.
Jupiter, being a planet, shines because it reflects the light of the sun.
Regulus is a star, so it shines by its own light.
If Regulus were at the sun’s distance from Earth, it’d visually be 150 times brighter than our sun. Or, another way of putting it, the sun at Regulus’ distance of 79 light-years would appear 1/150th as bright as Regulus. You’d need an optical aid to see the sun at this far away.
The moon travels in front of all the constellations of the zodiac in about four weeks. As seen from Earth, the moon moves much more quickly relative to the backdrop stars of the zodiac than does any other celestial object.
For instance, the moon will move past Jupiter on June 11, and then will leave the constellation Leo to enter the constellation Virgo after a few more days.
Jupiter won’t enter Virgo until August 8, 2016.
Bottom line: Watch for the moon and the planet Jupiter to light up the constellation Leo the Lion as soon as darkness falls on June 10, 2016.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.