Sky ArchiveTonight

Moon to sweep by Jupiter and star Antares

From around the world on the evenings of June 14, 15 and 16, 2019, look for the moon and then for the red supergiant star Antares and the giant gas planet, Jupiter. The moon – now in a waxing gibbous phase, moving toward full moon on the night of June 16-17 – will pass to the north of Antares and Jupiter.

Despite the moon’s glare, you should be able to see Antares and Jupiter relatively easily. Antares counts as a 1st-magnitude star, and Jupiter is far brighter than any star (except our sun), outshining Antares by nearly 30 times. Remember, though, that Antares, being a star, shines by its light. Jupiter shines only by reflecting sunlight.

As the Earth spins beneath the heavens, moving from west-to-east on its rotational axis, the moon, Antares and Jupiter will appear to parade westward across the sky throughout the night. However, this supposed motion of the moon, Antares and Jupiter is really a reflection of the Earth spinning on its rotational axis.

What’s more, even as the moon goes westward throughout the night, it’s simultaneously moving eastward in front of the stars and bright planets of our solar system. Throughout the night, the moon moves about 1/2 degree (its own angular diameter) eastward in front of the constellations of the zodiac. In one day (24 hours), the moon journeys some 13 degrees eastward upon the zodiac.

You can see the moon’s daily change of position for yourself these next several nights. Note the moon’s position relative to Antares and Jupiter on June 14. At the same time on the following evenings – June 15 and 16, 2019 – see how far the moon has moved. Watch for the moon to sweep to the north of the star Antares and then the king planet Jupiter. The moon’s daily change of position is due to the moon orbiting our planet Earth.

Planets in order, large views of each, next to section of the sun.
Sizes of planets to scale but distances from sun are not. Image via Wikipedia.

Jupiter is truly the giant planet of our solar system, having about 2 1/2 times the mass (heaviness) of all the other planets in the solar system combined. The diameter of Jupiter is about 11 times that of Earth. Yet, you have to square this diameter figure (11) to find that Jupiter’s surface area exceeds that of our planet Earth by 121 times (11 x 11 = 121). And you have to cube this diameter figure to find out that Jupiter’s volume exceeds Earth’s by about 1,331 times (11 x 11 x 11 = 1331).

But Jupiter is still small fry when comparing the king planet with our sun. The sun has a diameter of about 10 Jovian diameters, yet a surface area of 100 times that of Jupiter and a volume 1,000 times that of Jupiter.

Yet, our sun is tiny in contrast to Antares. The size of this red supergiant star is not known with precision. Its diameter is estimated to be somewhere around 340 to 400 solar diameters. I’ll let the inquiring reader figure out Antares’ surface area and volume in solar units.

Sun as tiny dot, Arcturus as much larger circle, part of Antares showing as gigantic circle.
If Antares replaced the sun in our solar system, its circumference would extend beyond the orbit of the fourth planet, Mars. Here, Antares is shown in contrast to another star, Arcturus, and our sun. Image via Wikimedia Commons.

Bottom line: On June 14, 15 and 16, 2019, watch for the moon to sweep to the north of the red supergiant star Antares and then the king planet Jupiter.

June 14, 2019
Sky Archive

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Bruce McClure

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