Skylights: May 2023

After having spent 25 days within the boundaries of Aries, the Sun enters Taurus on May 14. The first 8:00pm sunset occurs on May 17. The Sun will not set earlier than 8:00pm until August 5.

Mercury reaches inferior conjunction on the 1st, ending its best evening apparition of 2023. Unfortunately, May’s morning apparition of our innermost planet will be less than ideal, with Mercury rising no more than an hour before sunrise by the 29th, when it will be at greatest elongation, 25° west of the Sun. This, combined with its position south of the ecliptic, means it will never be more than a few degrees above the horizon in the pre-dawn sky in May. Perhaps most notable, the 28-day waning crescent Moon will be 6° to the left of Mercury on the morning of the 18th.

As Venus treks its way eastward through the Winter Hexagon throughout May, note some conspicuous alignments and positions. It will cross the north-south axis (the line connecting Capella and Sirius) on the 6th, and will then be in the eastern half of the familiar winter asterism. On the 9th, it will be just 1.7° north of the open cluster M35 in Gemini. On the 16th, it bisects the northeast chord (the line connecting Capella and Procyon). Note also on the 16th, Mars will be in line with Castor and Pollux. Throughout the second half of the month, watch Venus’s changing position with respect to these two stars, as well as its approach to Castor and Pollux, until it finally “exits” the Winter Hexagon on the 30th.

Observing the phases of Venus telescopically can be challenging due to its overwhelming brilliance, especially when the planet is distant and in the wide gibbous phases, but it is now within 1 AU, and is beginning to appear fairly large in the eyepiece. In early May, Venus subtends 17 arcseconds as a 66% illuminated gibbous, and by month’s end, its 23 arcsecond globe is approaching 50% illumination. 

Latest Venusset occurs at 11:40pm EDT, on the 21st.

On the 22nd and 23rd, the waxing crescent Moon joins Venus in the evening sky.

Just as Venus is getting closer and brighter, Mars is becoming more distant and dimmer, though, at magnitude 1.4, still comparably bright to nearby Pollux and Castor. On the 16th, the Red Planet enters Cancer, and is within the same binocular field of view as the open cluster M44 by month’s end.

Telescopically, Mars won’t reveal much detail, as it reaches a distant 2 AU at the end of May, and its tiny globe is only 4.7 arcseconds across.

Jupiter passed conjunction in mid-April, and by mid-May it becomes visible low in the east before sunrise. The 27-day waning crescent Moon joins Jupiter in the morning of the 17th, at an apparent distance of just 1.8°, a spectacular pairing worthy of a look with a telescope or binoculars. Jupiter enters Aries two days later, on the 19th.

Saturn is located in Aquarius, and rises just after 3:00am EDT at the beginning of the month, and about 1:30am EDT at the end of the month. It reaches its point of western quadrature (elongation 90° west of the Sun) on the 28th, and clears the horizon enough to observe with a telescope. Quadrature is one of the best times to observe Saturn because this coincides with the point where the angle between Sun and Earth as seen from Saturn is at its widest (5.9°), making the shadows on Saturn and its rings as seen from Earth most pronounced.

You may also notice that Saturn’s ring plane angle is smaller than it has been. The ring plane is tilted about 9° in May, compared to about 15° a year ago. The rings plane angle will continue to decrease, on average, until March 2025, when it becomes 0°.

Uranus is in conjunction on the 9th and will not be visible until mid-June.

Neptune is located in Pisces, 4.7° south-southeast of gamma Piscium, in the Circlet asterism. The 25-day waning crescent Moon lies 4.0° east of the distant ice giant on the 15th.

Dwarf planet Ceres completes its retrograde loop a few degrees east of Denebola (Beta Leonis) in May, and resumes eastward motion near the intersection of Leo, Coma Berenices and Virgo, finally exiting through Virgo.

Dwarf planet Pluto, now located in western Capricornus, is 1.3° southeast of globular cluster M75. At a distant 34.3 AU, Pluto shines at a dim 14.5 magnitude.  

The Moon is 2.0° north of Spica on the 3rd.

The Full Flower Moon occurs on the 5th, with a penumbral eclipse occurring on the opposite side of Earth. On this day, the Moon sets at 5:26am and rises at 8:05pm EDT. Notice that a few minutes past midnight on the 5th, the Moon and Arcturus transit at about the same time.

The Moon passes 2.9° west-northwest of Antares on the 7th. Last quarter Moon is on the 12th.

New Moon occurs on the 19th, and for the week leading up to first quarter on the 27th, it passes some notable objects: 4.5° NW of M35 on the 21st, 5.1° W of Venus on the 22nd, 2.0° S of Pollux on the 23rd, 3.0° N of M44 on the 24th, and 3.2° N of Regulus on the 26th.

On the last night of May, the Moon returns to the same place it was on the first day, a few degrees from Spica.

In early May we get our last look at many of our winter sky’s familiar star patterns. Drawing a horizontal line parallel with the western horizon, from left to right, we see Sirius, the Belt of Orion, and Taurus’s two prominent clusters, the Hyades and Pleiades, all in position for their seasonal departure from our springtime evening sky. By mid-May, all but Sirius will have dipped out of sight, leaving only the northeastern chord of Winter’s Hexagon, which now forms a great chevron, arcing from Procyon in the west, up to Pollux and Castor, and connecting to Capella in the northwest. The familiar asterism also appears to change nightly, with the eastward march of Venus and Mars through it.

To the east, the stars of summer are beginning to make their evening appearance. Soon after twilight in early May, Vega can be seen hovering over the northeast horizon, and by month’s end, Deneb (alpha Cygni) can be seen low in the northeast, and Antares (alpha Scorpii) is visible in the southeast. By midnight, the Summer Milky Way once again arcs across the sky.

High overhead facing north, the Big Dipper’s pointer stars are at their upper culmination at the beginning of the month. As the hours and days advance, the Big Dipper can be seen pivoting into the western sky.

In the south during early evenings in May, the sky is dominated by Leo, but several dim constellations await exploration, including Hydra, the water snake, which is the longest constellation, and shares a border with 13 others. Its second magnitude star Alphard, meaning “the lonely one,” is reminiscent of Fomalhaut (alpha Piscis Austrinus) in the autumn sky, in that it occupies an area of sky relatively devoid of other bright stars. Alphard is a class K giant star that lies about 180 light years away and shines with the brilliance of 950 Suns. 

Following the dim, meandering stars towards the tail of the water snake, we come across a conspicuous, non-symmetrical quadrilateral of third magnitude stars which lie about 15 degrees to the west-southwest of the bright, hot blue Spica (alpha Virginis). This is Corvus, which, with a generous helping of the imagination, and perhaps aided by a dark sky to reveal some of its dimmer members, represents a crow. 

Corvus hovers over the south during evenings in May, and is worthy of a visit by observers with a telescope. Although technically located within the neighboring constellation Virgo, Corvus is typically the hopping-off point for a journey to the notable lenticular galaxy Messier 104, familiarly known as the Sombrero Galaxy. 

Starting from Algonab (delta Corvi), jump just 5.5° slightly more north than northeast to find an 8th magnitude glow, elongated roughly east to west. If you are manually driving your telescope and have a bit of difficulty landing on M104 at first, you may arrive at two small and very distinct asterisms nearby that will help guide you to it. The first is a triangular asterism about 6 arcminutes across known as “the stargate.” A close pair of 8th magnitude stars in its center are surrounded by three stars spaced at approximate equal angles. The two brightest stars on the perimeter are approximately the same brightness, at 6th magnitude, and the dimmer, northern component gives the asterism its slight asymmetric appearance. From the center of the stargate, follow a line through this dimmer star and continue northeastward just under one degree. Here, you will find another helpful asterism in the shape of a small arrow, consisting of four 9th magnitude stars that point in a southeasterly direction. Follow this arrow directly to M104, just 1/3° away.

Although M104’s 8th magnitude glow is visible in small telescopes on a moonless night, a larger aperture (about 6-to-8 inches) will be needed to see its most distinguishing feature: a thick, opaque ring of dust that bisects the galaxy’s central bulge. The Sombrero moniker originated from old photographs where the galactic core is overexposed, and the dust ring represents the wide brim of the namesake hat. Through the eyepiece of your telescope, the combined light of about 100 billion stars has traveled 29 million light years. The galaxy has a mass of about 800 billion Suns, a bit more than half that of the Milky Way, and is about half of the Milky Way’s radius. Recent observations from Hubble Space Telescope have revealed that M104 has about 2,000 globular clusters, an order of magnitude more than the Milky Way.