The Pretty Crescent Moon Kisses Venus, Sunday’s New Moon is an Annular Eclipse, the Solstice Starts Summer, and a Tour of Hercules!

This image of the Messier 13 globular star cluster in Hercules was taken by Martin Pugh. The cluster is composed of thousands of old, blue and yellow stars collected into a spherical ball orbiting our galaxy’s core. It’s located about 25,000 light-years from our sun. This image spans about 30 by 40 arc-minutes, slightly larger than the full moon. NASA APOD for June 14, 2012

Hello, Summer Stargazers!

Here are your Astronomy Skylights for the week of June 14th, 2020 by Chris Vaughan. Feel free to pass this along to your friends and send me your comments, questions, and suggested topics. You can also follow me on Twitter as @astrogeoguy! Unless otherwise noted, all times are expressed in Eastern Time.

I can bring my Digital Starlab portable inflatable planetarium to your school or other daytime or evening event, or teach a session online. Contact me through AstroGeo.ca, and we’ll tour the Universe or the Earth’s interior together!

Northern Hemisphere summer begins with the solstice this week. For skywatchers the world over, the moon will rise in the wee hours and remain visible during daytime mornings. The moon will also “kiss” the new Morning Star, Venus on Friday, and appear at new moon in an annular solar eclipse! Jupiter and Venus will rise together in late evening. The moon’s absence from night-time skies will let us explore early-summer treats, including the double stars and globular clusters of Hercules. Here are your Skylights!

The June Solstice starts the Northern Summer

The beginning of summer for the Northern Hemisphere, known as the June Solstice or Summer Solstice, occurs on Saturday, June 20 at 5:44 pm Eastern Daylight Time. At that moment, the northern end of Earth’s axis of rotation will be tipped by 23.5° towards the sun. As a result, the sun will reach its highest noonday position in our sky for the year, sunlight will shine more intensely on the Northern Hemisphere, and we northerners will receive our longest amount of daylight. More hours of concentrated sunlight translates to more solar energy and warmer days! It is NOT the case, as some people think, that we are warmer in summertime because we are closer to the Sun. That scenario, called perihelion, actually happens in early January every year! As a matter of fact, the Earth is now only two weeks away from reaching its greatest distance from the sun, or aphelion, for this year. That will occur on July 4.

For our friends in the Southern Hemisphere, this solstice signals the sun’s lowest noon-time height for the year, and marks the start of their winter. The June solstice is eagerly awaited by Northern Hemisphere astronomers because, after Saturday, their days will slowly start to get shorter while their nights lengthen.

The Moon

The moon reached its last quarter phase this morning (Sunday) at 2:24 am Eastern Time. The term “last quarter” is not derived from the moon’s appearance, which is half-illuminated – on its western (left-hand) side. Instead, the phrase describes its progress around Earth. After this phase, the waning moon will traverse the final quarter of its orbit around the Earth, on the way to new moon on the coming weekend.

Between last quarter and new moon, our natural satellite always rises in the hours before dawn, and then remains visible in the morning daytime sky all around the world. I encourage you to view the moon in binoculars and telescopes during the daytime – but take care to avoid pointing those optical aids anywhere close to the sun, especially if you allow youngsters to use them. Parental supervision is a must! The moon’s absence from the evening sky also means darker nights and better conditions for seeing the dimmer deep sky targets.

Around last quarter, the moon’s topography is dramatically illuminated by slanted sunlight, especially along the pole-to-pole terminator boundary that divides the lit and dark hemispheres. In contrast to our views of the moon during evening, the morning moon’s sunlight is coming from the opposite direction – so it illuminates the familiar features in a much different way. Try it!

From Monday to Wednesday morning before dawn, the moon will shine as a pretty, waning crescent among the medium-bright stars of the water constellations Cetus (the Whale) and Pisces (the Fishes). On Thursday and Friday, the moon will cross into Taurus (the Bull), where it will join the newly-minted “morning star” Venus low in the east-northeastern sky! On Friday, the moon and Venus will be so close that they’ll fit together in the field of view of binoculars and in backyard telescopes at low magnification, where they will both show a slim crescent phase. The pairing will also make a nice widefield photograph when composed with foreground scenery. Observers in the Azores, the Canary Islands, far northern and eastern Canada, Greenland, and the northern parts of Europe, Russia, and Mongolia can watch the moon cross in front of (or occult) Venus between 07:20 and 08:07 Greenwich Mean Time.

Friday morning will also be our last chance to see the moon until next Monday – with one cool exception! When it reaches its new phase on Sunday, June 21 at 2:41 am EDT, or 6:41 GMT, the moon will be travelling between the Earth and the sun. Since sunlight is only shining on the side of the moon aimed away from Earth, and the moon is in the same region of the sky as the sun, the moon is normally hidden from view everywhere on Earth for about a day. But this new moon will occur 6.2 days past apogee, the moon’s maximum distance from Earth, resulting in a thin-ringed annular solar eclipse visible across central Africa and southern Asia.

During an annular solar eclipse, a ring of sunlight remains visible around the moon at totality because the moon is too far from Earth to completely block the sun. The path of totality for this eclipse will commence at 04:48 GMT in central Africa. Greatest eclipse, with 98.8% of the sun blocked by the moon, will occur for 38 seconds at 06:40:05 GMT in northeastern India, with the sun nearly overhead. After crossing southern China and a final landfall over Taiwan, the moon’s shadow will sweep across the Philippine Sea and Pacific Ocean, narrowly missing Guam ten minutes before sunset. The partial eclipse will be visible throughout eastern Africa, southern Europe and the Middle East, most of Asia, and Southeast Asia. The eclipse will be live streamed on YouTube and elsewhere. Remember – proper solar filters will be required to view any portion of this eclipse in person.

The Planets

The first few nights of this week will offer you a chance to catch Mercury sitting very low over the west-northwestern horizon after sunset. The speedy little planet is swinging between Earth and sun, so it will move lower and closer to the sun each consecutive night. Your best viewing time falls around 9 to 9:15 pm in your local time zone. Observers living closer to the equator, where the ecliptic stands upright, will see Mercury in a darker sky. For reference, Mercury will be situated a generous fist’s width directly below (or 12 degrees to the celestial southwest of) the two bright stars Castor and Pollux in Gemini (the Twins).

The next planets appear in late evening. Bright, white Jupiter will rise before 11 pm local time this week (and then even earlier as the weeks tick by). Dimmer, yellowish Saturn will rise about 15 minutes later. All summer long, the two gas giant planets will sit only a slim palm’s width apart in the sky, with Saturn on the left (east). In the wee hours of the night, Jupiter might catch your eye through a southerly window because the planet won’t climb any higher than about 23 degrees above the horizon. By dawn you’ll find the two planets sitting not very high above the southwestern horizon. Saturn will disappear into the brightening sky before Jupiter.

This week, the globular star cluster named Messier 75 (or NGC 6864) will still be positioned below and between Jupiter and Saturn. The magnitude 9.2 cluster should be visible in binoculars and backyard telescopes as a small, fuzzy patch. The cluster will be located approximately two finger widths below (or 1.5 degrees to the celestial south of) the two much brighter planets. Every morning, the planets will shift a little bit to the right (west) compared to the cluster. So it will move closer to Saturn than Jupiter this week.

Even binoculars will reveal Jupiter’s four large Galilean moons named Io, Europa, Ganymede, and Callisto as they dance around the planet from night to night. And a modest-sized telescope will show Jupiter’s brown equatorial belts, and the famous Great Red Spot. In the Eastern Time zone, the Great Red Spot will be crossing the planet’s disk before dawn on Monday morning, after midnight on Tuesday morning, during the wee hours of Thursday morning, and before dawn on Saturday morning.

From time to time, the small, round, black shadows cast onto Jupiter by its Galilean moons become visible in amateur telescopes as they cross (or transit) the planet’s disk. On Thursday, June 18, observers across Asia can see a rare double shadow transit. At 18:33 GMT, Ganymede’s larger shadow will join Europa’s smaller shadow already in transit. 40 minutes later Europa’s shadow will move off the planet at 19:13 GMT, leaving Ganymede’s shadow to complete its crossing hours later. Tonight (Sunday) after midnight, observers in the Americas can see Europa’s shadow cross Jupiter until 1:55 am EDT. On Sunday morning, June 21, Io’s shadow will cross between 3:20 and dawn.

Dust off your telescope! Even a small telescope will show Saturn’s rings and several of its brighter moons – especially its largest moon, Titan! Because Saturn’s axis of rotation is tipped about 27° from vertical (a bit more than Earth’s axis), we can see the top surface of its rings, and its moons can arrange themselves above, below, or to either side of the planet. During this week, Titan will migrate counter-clockwise around Saturn, moving from the left of Saturn tonight (Sunday) to below the planet next Sunday. (Remember that your telescope will flip the view around.)

Mars has been speeding eastward along the ecliptic, causing it to rise much later than Jupiter and Saturn. This week, Mars will be rising at about 1:30 am local time, and will remain visible as a prominent reddish dot until dawn, when it will be positioned about three fist diameters above the southeastern horizon. Mars is steadily increasing in disk size and brightness because Earth is travelling towards it this summer.

In the eastern evening sky on the evenings surrounding Sunday, June 14, the orbital motion of the main belt asteroid designated (2) Pallas will take it 1.5 finger widths to the upper left (or 1.5 degrees to the celestial north) of the Coathangar Cluster in the constellation of Vulpecula (the Fox). Also considered an asterism, the Coathangar is an easy target for binoculars – located midway between the bright stars Vega and Altair. The magnitude 8.94 asteroid and most of the cluster’s stars will appear together in the field of view of backyard telescopes at low magnification.

Venus has become the “Morning Star”, shining brightly in the eastern pre-dawn sky, where it will stay for the rest of 2020. Venus will become easier to see every week.

Exploring Hercules

With the Moon out of the evening sky worldwide this week, we have excellent conditions for viewing the sky’s best sights. Shortly after it’s dark on the next clear evening, head outside point your finger directly overhead. That’s the zenith. While objects occupy that position, they will always appear at their best because you are looking through the least amount of intervening air. During late evening in mid-June every year, the constellations of Boötes (the Herdsman), Corona Borealis (the Northern Crown), Hercules sit just below the zenith, high in the southern sky. Let’s focus on Hercules, which contains one of the summer season’s best objects!

Hercules isn’t composed of very bright stars, but you can still find it very easily, even from mildly light-polluted skies. Face southeast and look for a very bright, white star sitting about halfway up the sky. That’s Vega, the extremely bright star in Lyra. Higher than Vega, in the southern sky, is another prominent star, orange-tinted Arcturus. Between these two stellar signposts is the realm of mighty Hercules.

Hercules’ body is defined by a very distinctive keystone-shaped quartet of modestly bright stars. The keystone is about 6° across (a palm’s width), with its wide end to the north (towards your left) and its narrow end pointed southwards (towards the lower right). The hero of mythology is upside down for Northern Hemisphere observers. His sharply bent legs extend upwards to the left, and his two arms are outstretched downward. The star that marks his eastern hand, named Maasym, or Lambda Herculis, is below the keystone. It combines with four other stars to form a loose chain of five stars running left-right, each separated by a couple of finger widths. In classical drawings Hercules is grasping the three-headed dog Cerberus, which he was tasked with capturing as one of his twelve labours.

Hercules is the fifth largest constellation by area, and was one of the original 48 constellations tabulated in the Almagest, an early astronomy book produced in ancient Greece by Ptolemy. The early Greeks depicted Hercules, with his legs bent – as “The Kneeler” praying to his father Zeus to aid him in an upcoming battle. Beyond his feet, to our upper left, are the stars of Draco (the Dragon), ready to be crushed under his feet. To the upper right (or celestial west) of Hercules is the little circlet of stars that form the distinctive constellation of Corona Borealis (the Northern Crown).

Starting in the keystone, the right-most and brightest star is designated Zeta Herculis (or ζ Her for short). This is a binary star system situated about 35 light-years away from us, where the pair of stars orbit around one another. Both stars are yellow sun-like stars, although the brighter star is more massive and luminous. Moving clockwise and downwards, we arrive at the dimmer white star Epsilon Herculis. Next, at lower left, is Pi Herculis. It’s a giant, orange-tinted, cool star situated about ten times farther away than Zeta. At the upper left corner of the keystone sits Eta Herculis. It is a yellowish, sun-like star, about ten times the diameter of the Sun, but a bit cooler than our sun.

Hercules contains quite a few double and binary stars within reach of a backyard telescope. One of the nicest ones is modest Rasalgethi, or Ras Algethi “Head of the Kneeler”, which sits about 1.6 fist diameters to the lower right (or 16° to the celestial southwest) of Epsilon Herculis. A medium-bright star named Rasalhague sits a slim palm’s width below Rasalgethi. In a small telescope, Rasalgethi easily splits into a lovely pair of orange and greenish stars. The slightly brighter one is a red giant class star that varies in brightness randomly over months to years. The partner is a yellow sun-like star that is itself a binary star too tightly spaced to resolve. The stars are about 360 light-years away and are orbiting one another with a period of 3,600 years. This double star, like many others, was given a single name centuries before telescopes revealed that there was more than one star there.

The brightest star in Hercules, Kornephoros “Club-bearer”, sits a fist’s diameter to the lower right of the keystone, where Hercules’ elbow would be. Only about two finger widths to the lower right (or 3° to the southwest) of Kornephoros is the double star Gamma (γ) Herculis. This is another pair that easily splits into two yellow stars in a modest telescope. But this double is a line-of-sight double star. The fainter star is actually much closer to us! Marsic or Marfik, which means “the Elbow” even though it’s at the end of his arm, is another “line of sight” double star that’s easy in a small telescope. Look for it about four finger widths to the right of Gamma.

Hercules contains one of my favorite objects, a globular cluster known as the Great Hercules Cluster or Messier 13 (or M13). This object is a tightly packed ball of at least 300,000 old stars. At magnitude 5.9, it is visible with unaided eyes under dark skies as a faint smudge, but reveals much more under magnification! It is located along the western (upper) edge of the keystone, about one-third of the way from the wide end. Your binoculars should pick it up. Midway between Hercules’ knees there is another, smaller globular cluster called Messier 92. This one is also readily visible in binoculars. A third, fainter globular cluster designated NGC 6229 sits 6.5°, or a palm’s diameter, to the lower right of M92.

Globular clusters are one of the most interesting classes of objects for stargazers. These spherical concentrations of old, densely packed stars orbit in the region just outside our Milky Way galaxy, and we’ve observed many of them around other galaxies, such as the Andromeda Galaxy. Viewed in a telescope under dark skies, they will look like a pile of salt poured onto black velvet – with a dense white center surrounded by a sprinkling of outlying stars. Each cluster looks different, varying in the scattering of stars. Photographs reveal that these objects contain a mixture of reddish, blue, and yellow stars in different proportions.

The Great Hercules Globular Cluster was first observed by British astronomer Edmund Halley in 1714 and later included as number thirteen in Charles Messier’s famous list of “not-a-comet” objects. At 21,500 light-years away, it is a relatively close member of that class of objects. It shines with a relatively bright magnitude of 5.8, and it actually covers an area of sky spanning 20 arc-minutes (or two thirds of the moon’s diameter)!

More than 150 of these clusters have been mapped around our galaxy. They are so densely packed that the stars in their interiors are extremely close together, stirring the imagination of those contemplating extraterrestrial intelligent life. Advanced civilizations on planets around stars embedded deep inside a globular cluster would be able to exchange radio messages on timescales of weeks or months – and travel between adjacent solar systems would not require the decades or centuries we would need to visit our nearest neighbours. In fact, M13 was also one of the first targets for potential contact with other civilizations, when a radio message was beamed there from the Arecibo Radio Observatory in 1974.

The stars of Hercules are host to at least fifteen known exoplanets, including one named TrES-4. At 1.7 times the mass of Jupiter, it’s one of the most massive exoplanets yet discovered. However, its calculated density is extremely low, about the same as cork! This is one of the hot-Jupiter class of exoplanets, with a surface temperature in excess of 2,000 C.

Let me know how your exploration of Hercules goes.

The Treats of Boötes

The absent moon over the coming week and the lovely June nights will offer a fine opportunity to explore the realm of Boötes (“Bow-OH-tees”), the Herdsman or Plowman. Last week, I described it and posted sky charts here.

Public Astro-Themed Events

Due to the COVID-19 virus, in-person public star parties and lectures have been cancelled or postponed for the moment. Here are some Internet-based astro-themed activities.

On Wednesday evening, June 17 at 7:30 pm EDT, the RASC Toronto Centre will live stream their monthly Recreational Astronomy Night Meeting at https://www.youtube.com/rasctoronto/live. Talks include the Sky This Month, a telescope DIY project, and how to polar align your telescope with software. Details are here.

Many astronomers are running broadcasts of the views through cameras attached to their telescopes while they describe the item and take questions. A search for the terms “star party” on YouTube and FaceBook should let you find live or pre-recorded sessions.

The Canadian organization Discover the Universe is offering astronomy broadcasts via their website here, and their YouTube channel here.

On many evenings, the University of Toronto’s Dunlap Institute is delivering live broadcasts. The streams can be watched live, or later on their YouTube channel here.

The Perimeter Institute in Waterloo, Ontario has a library of videos from their past public lectures. Their Lectures on Demand page is here.

Space Station Flyovers

There are no visible ISS (or International Space Station) flyovers for the GTA this week.

Keep looking up, and enjoy the sky when you do. I love questions and requests. Send me some!