On May 3, 4, and 5, 2021, watch for the Moon to pass by Saturn and Jupiter. In today’s article, we’ll talk about the astronomical terms describing the meeting of the Moon and the gas giants and tell you how and when to observe them in the sky above you.
What’s the difference between an appulse and conjunction?
In astronomy, two related terms are used to describe a close approach of two celestial objects in the sky. An appulse refers to a close approach of two sky objects, when the apparent distance between them is the least, as seen from the Earth. A conjunction, in turn, occurs when two heavenly bodies align so that they share the same right ascension or ecliptic longitude. Generally, the exact time of an appulse differs from that of conjunction; sometimes, an appulse might take place without a conjunction.
The Moon meets the gas giants
On May 3, 2021, at 12:58 EDT (16:58 GMT), the conjunction of the Moon and Saturn will occur; at this moment, these celestial objects will have the same right ascension. Our natural satellite will shine at a magnitude of -11.9, while the ringed planet will have a magnitude of 0.5. An appulse will take place a little later — at 14:49 EDT (18:49 GMT). At this moment, the Moon and Saturn will make the closest apparent approach, passing within 4°02' of each other. Both sky objects will be situated in the constellation Capricorn; learn more about this beautiful constellation and its prominent stars in our recent article.
Continuing its journey across the sky, the Moon will enter the constellation Aquarius, where it will meet another gas giant, Jupiter. The conjunction of the Moon and Jupiter will take place on May 4, 2021, at 17:02 EDT (21:02 GMT); it will be followed by the appulse a couple of hours later when the apparent separation between the Moon and the gas giant is 4°21'. Jupiter is about 11 times brighter than Saturn: it will shine at a magnitude of -2.3.
You can observe the gas giants in the pre-dawn sky these days. Golden Saturn rises with the stars of central Capricorn first; the largest planet of the Solar system, brilliant Jupiter, joins the ringed planet about half an hour later. The separation between these planets increases slightly every morning.
Enjoy the dance of the Moon and the gas giants with Star Walk 2. The stargazing guide will help you locate the Moon, Saturn, and Jupiter in the sky above you, determine the best time for observation and identify the stars and constellations surrounding them.
What is the Last Quarter Moon?
On May 3, only a few hours after joining Saturn, the Moon will reach its last quarter phase or west quadrature, and we’ll see the half-illuminated lunar disk adorning the sky. Our natural satellite is considered to be at dichotomy when it appears half-lit by sunshine, while a quadrature designates the configuration when the Moon is 90° from the Sun in the sky. In common usage, the terms quadrature and dichotomy are often thought to be synonyms because these two events happen almost concurrently. However, at a quadrature, more than 50% of the Moon is illuminated, but by such a small amount that it’s impossible to discern visually.
Around what time of day would the Moon rise if it is in the last quarter phase? The Last Quarter Moon rises around midnight; also, it appears at its highest in the sky around dawn and sets around midday. To get more information about the Moon’s phases and find out the exact times of the moonrise and moonset, launch the Star Walk 2 app, tap the Menu icon in the lower-right corner of the screen, and go to the Sky Live section.
By the way, Saturn also reaches its west quadrature on the same day. At this moment, the Sun-Earth-Saturn angle will equal 90°, while the Earth will reside at its vertex. However, unlike the Moon, the ringed planet won’t appear half-illuminated at quadrature. Saturn is a superior planet (which means that it orbits the Sun outside of the Earth’s orbit), and it always appears (nearly) full on the sky’s dome.
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