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The Night Sky of May

Dr. Wayne Wooten
Professor of Astronomy

For May 2024, the moon is last quarter on May 1st. On May 3rd, the waning crescent in the dawn passes just south of Saturn, then close to Mars and Mercury on May 6th. It is new on May 8th, a month after the historic totality in April. First quarter moon is May 15th, and the Full Flower Moon on May 23rd. It returns to last quarter on May 29th, marking the 27.3 day long synodic month for the moon to return to the same phase (last quarter in this case). And it again passes slow moving Saturn on May 31st, marking the 29.5 day sidereal month to return to the same place among the stars. This two-day difference in these months is of course due to the fact that the moon is moving along with our revolving earth around the Sun, so it needs these two extra days to play catch up with our earth-sun alignment with the background stars!

Mercury is in the dawn, and at greatest western elongation at mid month. Venus is lost in the Sun’s glare, not to return to the evening skies until summer. Mars is low in the east at dawn, and will not be back in the evening skies until winter. Jupiter is vanishing into the sun’s glare at dusk as well. Only Saturn, well up the dawn sky, is far enough from the Sun for good telescopic viewing, and its rings are closing down, compared to last year, as it approaches its own equinox, when its rings disappear with earth based scopes as we view them edge on.

While the naked eye, dark adapted by several minutes away from any bright lights, is a wonderful instrument to stare up into deep space, far beyond our own Milky Way, binoculars are better for spotting specific deep sky objects. For a detailed map of northern hemisphere skies, about April 30th, visit the www.skymaps.com website and download the map for the new month; it will have a more extensive calendar, and list of best objects for the naked eyes, binoculars, and scopes on the back of the map. Also available is wonderful video exploring the sky, available from the Hubble Telescope website at: www.hubblesite.org/explore_astronomy/tonights_sky. Sky and Telescope has highlights at www.skyandtelescope.com/observing/astronomy-podcasts for observing the sky each week of the month.

 

The winter constellations will soon be swallowed up in the Sun’s glare, but Orion is still visible, with its famed Orion Nebula, M-42, seen below the three stars marking his famed belt. Dominating the southwest is the Dog Star, Sirius, brightest star of the night sky. When Sirius vanishes into the Sun’s glare in two months, this sets the period as "Dog Days".

The brightest star in the NW is Capella, distinctively yellow in color. It is a giant star, almost exactly the same temperature as our Sun, but about 100X more luminous. Just south of it are the stellar twins, the Gemini, with Castor closer to Capella, and Pollux closer to the Little Dog Star, Procyon.

Overhead, the Big Dipper rides high. Good scouts know to take its leading pointers north to Polaris, the famed Pole Star. For us, it sits 30 degrees (our latitude) high in the north, while the rotating earth beneath makes all the other celestial bodies spin around it from east to west.

If you drop south from the bowl of the Big Dipper, Leo the Lion rides high. Note the Egyptian Sphinx is based on the shape of this Lion in the sky. The "regal" star Regulus marks the heart of the celestial lion. Taking the arc in the Dipper’s handle, we "arc" SE to bright orange Arcturus, the brightest star of spring. Cooler than our yellow Sun, and much poorer in heavy elements, some believe its strange motion reveals it to be an invading star from another smaller galaxy, now colliding with the Milky Way in Sagittarius in the summer sky. Moving almost perpendicular to the plane of our Milky Way, Arcturus was the first star in the sky where its proper motion across the historic sky was noted, by Edmund Halley. Just east of Arcturus is Corona Borealis, the "northern crown", a shapely Coronet that Miss America would gladly don, and one of few constellations that look like their name. The bright star in the crown’s center is Gemma, the Gem Star. But it may be rivalled in just a few days or weeks!

Keep checking out the lower right rim of the crown nightly. Science is based on understanding a phenomena well enough to make predictions, and if our understanding of the dwarf novae outbursts is right, the "Blaze Star", T Corona borealis may erupt between now and September! Based on its last two outbursts, it may rival Polaris at second magnitude for a few days, making it surpass Gemma in brightness, but fade back to 10,000 times fainter at 10th magnitude.

Spike south to Spica, the hot blue star in Virgo, then curve to Corvus the Crow, a four-sided grouping. The arms of Virgo harbor the Virgo Supercluster of Galaxies, with thousands of "island universes" in the Spring sky. We are looking away from the place of thickly populated Milky Way, now on the southern horizon, toward the depths of intergalactic space.

Because we live farther south than most Americans, we get a fine view of the closest and brightest globular star clusters, Omega Centauri, on May evenings. From a dark sky site, you can spot it with your naked eyes about 12 degrees above the southern horizon when it is at its highest in the south, about 9 PM at the end of the month. Ideally, observe it at the beach, where the Gulf is your southern horizon. It is fine in binoculars, and resolves beautifully into about a million sun with larger scopes. Here Dr. Dave John Kreiger catches it from Gulf Shores, Alabama with his See Star S 50.

To the northeast Hercules rises, with his body looking like a butterfly. It contains one of the sky’s showpieces, M-13, the globular cluster faintly visible with the naked eye. Find it with the T Corona borealis chart on the previous page midway on the top left wing of the cosmic butterfly, then take a look with a larger telescope and you will find it resolved into thousands of stars! Still, it is smaller and farther away than omega, and pales in comparison, but is high enough to be observed for observing it for several hours. Omega is only out for about two hours an evening in the far southern sky.

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