This week, the moon reaches its first quarter phase, and in celebration cruises past the star Regulus in the constellation Leo, the lion. Regulus is part of the northern hemisphere’s Spring Triangle (see last week’s Starwatch) and so is well placed in the southern sky this week.
The chart shows the view looking south at 22.00BST on 15 May 2024. At the time of the conjunction, the moon will be 7.9 days old, so will have just crept past the exact moment of first quarter. Instead of being a waxing crescent, it will be a waxing gibbous moon with 55.7% of its visible surface illuminated. Regulus is about four times more massive than the sun, and has a surface temperature of 11,500K – around double our own sun’s 5,700K.
Both stars are in the stable “middle-aged” sections of their lives. This is known as the main sequence and involves the stars generating power by converting hydrogen to helium via nuclear fusion reactions. The conjunction can also be seen easily from the southern hemisphere, although depending on the observer’s longitude, the moon might not be quite so close to Regulus during the hours of darkness.
