Waxing Gibbous Moon and Antares, A Mid-June Southern Summer Spectacle

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A view to the south tonight at 11:30 PM, EDT with the moon 4 degrees north of Antares. Image content via Stellarium, gif created via ezgif.com.

Tonight’s southern vista features the waxing gibbous moon 2 days before full, 4 degrees north of the heart of the Scorpion, the red supergiant star Antares. For complete ephemerides of the moon, including phase, please visit Time and Date. The current phase of the moon is always displayed on any of our articles or pages in the upper right.

Why is the moon so close on the sky to Antares and Scorpio?

Scorpio is one of the 12 constellations of the Zodiac, the constellations through which the path of the ecliptic passes. All principal solar system objects will appear on or near this imaginary path on the sky, the path that represents the plane of the solar system. Those principal solar system objects include the moon.

June 2009’s Strawberry (full) moon with Antares less than 1/2 degree to the east (left), just emerging from a ‘Lunar Occultation’, a rare event where the moon passes in front of or ‘occults’ an object of interest. Image, courtesy the author.

Scorpio and Antares

At a distance of approximately 550 light years, Antares is a high-mass (10-12 solar mass), highly evolved red supergiant star that will soon end its life in spectacular fashion as a Type-II supernova. Previously, we presented a vista from Chile, showcasing the ethereal majesty of our galaxy’s Galactic Center with Scorpio and Sagittarius prominently placed due south as it is now.

A high resolution view of Antares, imaged by ESO’s Very Large Telescope (VLT) at Paranal, Chile.

Note the striations on Antares’ photosphere, features indicative of a strong convection just below the photosphere. These convection cycles transport the superheated gas (the brighter regions) from the star’s interior to the ‘surface’ for radiation. The darker features indicate cooler regions that are descending back into the interior. These variations in photospheric gas temperature are similar to ‘sun spots’ on our home star, the sun.

Almost due west of Antares is the globular star cluster, Messier (M)-4, a summer favorite of amateur and professional astronomers alike and astrophotographers.

In this view we ‘zoom’ to Antares with Messier-4 flanking the Red Supergiant star to the west. Image content via Stellarium, gif created via ezgif.com.

Globular Clusters and Messier 4

Messier-4 as imaged with the Hubble Space Telescope

At over ten times the distance to Antares and directly to its west (right) in the image above is Messier-4 (M-4), a globular star cluster in the last frame of the animated image above. In the Hubble Space Telescope image to the left, we see the diverse stellar population consisting of evolved red giant and horizontal branch stars, blue stragglers and ancient population II stars.

All constituent stars of a globular cluster formed at the same time and from the same cloud of gas and thus constitute a ‘single stellar population’. This singular aspect of globular clusters provides a unique insight into stellar formation and evolution. Additionally, since many constituent stars date to the earliest epoch following recombination, careful analysis of their spectra and composition provides additional confirmation of the age of the universe of 13.772±0.040 billion years.

Although visible in a pair of binoculars as a soft, fuzzy globe, a telescope is required to reveal its true nature as an agglomeration of over 60,000 stars, all gravitationally bound together. Stars in these clusters, compared to the hot, young stars in galactic clusters such as M-7 or M-45, the Pleiades, are among the oldest stars in the universe.

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