Be sure to watch the magnificent pairing of the moon and Jupiter as darkness falls on these next few evenings – April 25, 26 and 27. The moon and Jupiter rank as the brightest and third-brightest heavenly bodies of nighttime. What’s the second-brightest? It’s blazing planet Venus, also beaming in your western sky at dusk on these April 2015 evenings.
You can easily tell Jupiter from Venus. Jupiter is that dazzling starlike object close to the moon in late April. The moon reaches its first quarter phase on April 25, 2015 at 23:55 Universal Time. Converting Universal Time to the clock time at North American time zones, the moon’s first quarter phase happens on April 25, at 8:55 p.m ADT, 7:55 p.m. EDT, 6:55 p.m. CDT, 5:55 p.m. MDT and 4:55 p.m. PDT.
At quarter moon, the moon’s disk is half-illuminated by sunlight and half-immersed in the moon’s own shadow.
The moon is said to be at first quarter because, in its cycle of phases, the moon is one quarter the way from one new moon to the next. Or you might say the moon is one-quarter of the way around Earth, as measured from one new moon to the next.
The lunar terminator – the shadow line crossing between the moon’s day and night sides – shows you where it’s sunrise on the waxing first quarter moon.
On the far side of the moon, the part you can’t see, the terminator marks the line of lunar sunsets.
On the other hand, let’s say you were on the near side of tonight’s first quarter moon, looking back at Earth. Then you’d see the waning last quarter Earth, and the earthly terminator would show you where it’s sunset on the waning last quarter Earth. From the waxing moon, you wouldn’t be able to view the terminator depicting sunrise on the far side of the waning last quarter Earth.
Because Jupiter is roughly in the same area of sky as the moon this evening, you might expect this world to exhibit a similar phase to tonight’s moon. Not so. Jupiter is so far distant from Earth that it always appears nearly 100% illuminated from our earthly perspective.
Bottom line: Jupiter is near the first quarter moon on April 25. Enjoy the waxing moon and the dazzling planet Jupiter on April 26 and 27, too!