Yom Kippur, Sunday Brings a Punymoon and Rare Double Spots on Jupiter, Mercury at Max Visibility, and Orionids Appear!

This image of the full moon was captured by Michael Watson of Toronto hours after it was full in September, 2017. Notice how the craters along the right-hand edge show some shadowing while the rest of the moon is “flat”. Michael’s gallery of wonderful astro-images are here.

Hello, October Stargazers!

Here are your Astronomy Skylights for the week of October 13th, 2019 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 Eastern Time. To subscribe to these emails please click this MailChimp link.

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

Yom Kippur and the Jewish Calendar

Astronomy is generally considered to be a secular science – but there is plenty of astronomy embedded within religious and cultural traditions around the world. Let’s look at Yom Kippur, which was observed last Tuesday and Wednesday.

Since ancient times, most cultures around the world have designed their calendars around the visible cycles of the moon, and the sun’s apparent passage through the stars. The Jewish lunisolar calendar uses the first appearance of the fresh, young crescent moon to begin a month. But the moon’s phases repeat every 29.5 days, so that missing half-day needs to be factored in by making some months 29 days in length – the chaser “missing” months, and others 30 days in length – the malei, “full” months.

To account for the ten-day difference between the length of the solar year and twelve 29.5-day lunar months, and to ensure that the calendar of Jewish festivals remains synchronized with the seasons, a leap-month is added every three years. On those years, the summertime month of Adar is observed twice consecutively.

Nissan, the first month in the Jewish calendar, begins with the new moon following the March Equinox. But the Jewish New Year, which is said to honour the anniversary of the creation of Adam and Eve, occurs on the first day of the seventh month, which is named Tishrei. That month always falls in September-October on our western Gregorian calendar.

The month of Tishrei hosts the Jewish High Holidays – Rosh Hashanah, Yom Kippur, Sukkot, Shimini Atzeret, and Simchas Torah. Rosh Hashanah, which marks Jewish New Year, falls on Tishrei 1. Yom Kippur “day of atonement” falls on the tenth day of the seventh month. This “Sabbath of Sabbaths” is the day when forgiveness of sins is asked of God.

According to Jewish tradition, God inscribes each person’s fate for the coming year into the Book of Life on Rosh Hashanah – but waits until Yom Kippur to “seal” the verdict. During the intervening ten Days of Awe, a Jew tries to amend their behavior and seek forgiveness for wrongs done against God and against other human beings. Yom Kippur is designed to focus attention only on those things which truly matter. Prayer and fasting are the hallmarks of this day and many refrain from other luxuries, like the wearing of leather shoes.

The traditional greeting for Yom Kippur is “G’mar Hatima Tova” (May you be sealed in the Book of Life), or the shorter version “G’mar Tov.” Yom Kippur concludes at dusk with a final blast of the shofar, a final cry as the gates of heaven are considered to close.

The Jewish, Christian, and Muslim calendars all share similar roots, which is why Passover and Easter, and Christmas and Chanukah, are often coincident. The Muslim calendar is allowed to drift due to the ten-day lunar-solar difference, but it resets every 33 years. Their New Year occurs at the Vernal Equinox.

The Muslim and Jewish calendars both rely upon religious clerics to visually spot the first crescent of the new moon – but that’s another story!

The Moon and Planets

The moon will occupy the evening sky worldwide during this entire week, while it transitions from a “puny” full moon tonight to last quarter next Monday. Meanwhile, the Earth’s neighboring planets, Venus and Mars, will both increase in visibility as they move farther from the evening and morning sun, respectively. And Mercury will reach peak visibility, too. Here are your Skylights!

Today (Sunday) at 5:09 pm EDT, the full moon of October, traditionally called the Hunter’s Moon, Blood Moon, or Sanguine Moon, will occur. In the western hemisphere, the moon won’t rise until after it is full – but it will still appear full all night long. Actually, in the hours after the full phase occurs, binoculars or telescopes will reveal that the craters arrayed along the moon’s eastern limb are casting shadows – while the rest of the moon will appear “flat”. (Remember that the moon’s eastern edge, or limb, is on the same side as west is, on Earth.)

Indigenous groups have their own names for the full moons, which lit the way of the hunter or traveler at night before modern conveniences like flashlights. The Ojibwe people of the Great Lakes region call this one Mshkawji Giizia, the “Freezing Moon”. The Cree people of North America call it Pimahamowipisim, the “Migrating Moon”, when the birds fly south.

The October full moon always shines in or near the stars of Cetus and Pisces. Since it’s opposite the sun on this day of the lunar month, the full moon rises at sunset and sets at sunrise. This full moon will occur a few days after the moon reaches its greatest distance from Earth, or apogee – producing the smallest full moon of 2019. The opposite of a Supermoon – perhaps this one should be called a Punymoon!

On Wednesday night, the waning gibbous moon will leave Pisces and Cetus and enter Taurus (the Bull). By dawn on Thursday, the moon’s orbital motion will bring it near the triangular face of the bull. But only observers in the Eastern Hemisphere can see the moon caress the bull’s northern cheek!

On Friday overnight, the approximately half-illuminated moon will land between the horns of Taurus, the upraised club of Orion (the Hunter), and the toes of Gemini (the Twins). That weekend moon will rise near midnight and linger into the morning daytime sky.

Mercury and Venus will continue to occupy the western post-sunset sky this week. Venus is currently shifting farther from the sun. The shallow evening ecliptic will prevent Venus from climbing above the glare of sunset for a while longer, but its bright magnitude -3.85 gleam will make it fairly easy to spot for a brief period after sunset, if you can find a low open horizon to the west-southwest.

Much less bright Mercury will be positioned less than a fist’s diameter to the left (or celestial southeast) of Venus this week. On the evening of Sunday, October 20, Mercury will reach its widest separation (25 degrees east) from the sun for the current apparition. With Mercury south of a shallowly dipping evening ecliptic, this has been a poor appearance of the planet for Northern Hemisphere observers, but an excellent one for those at more southerly latitudes. The optimal viewing period for mid-northern latitudes falls between 6:45 and 7 pm local time. Viewed in a telescope Mercury will exhibit a waning gibbous phase. (Venus will look almost fully illuminated.)

Jupiter will be setting in the west soon after 9 pm local time this week, but the earlier-arriving sunsets of October are still giving time to view the spectacularly bright planet. As the sky begins to darken this week, look for the giant planet sitting less than two fist diameters above the southwestern horizon. Jupiter has spent this entire year below the stars of Ophiuchus (the Serpent-Bearer) and above Scorpius (the Scorpion). It will spend next year sitting quite close to Saturn!

On a typical night, even a backyard telescope will show you Jupiter’s two main equatorial stripes and its four Galilean moons – Io, Europa, Callisto, and Ganymede looking like small white dots arranged in a rough line flanking the planet. Good binoculars will show the moons, too! If you see fewer than four dots, then the missing ones are in front of Jupiter, or hidden behind it. Or, it might be that some moons are not being illuminated by sunlight because they are in eclipse!

From time to time, the small, round, black shadows cast onto Jupiter’s surface by those four Galilean moons become visible in amateur telescopes as they cross (or transit) Jupiter’s disk. Tonight, Sunday evening, October 13, observers in the Americas can see a rare double-shadow transit on Jupiter. At dusk, Europa’s shadow will be midway across the northern hemisphere of the planet – accompanied by the Great Red Spot. Shortly before 8 pm EDT, Io’s shadow will join in the fun. Two shadows will both be visible for approximately 35 minutes – until Europa’s shadow moves off the planet at about 8:28 pm EDT. Io’s shadow transit will end at 10 pm EDT – after the planet has set for more easterly observers.

The story will repeat next Sunday evening, October 20 – but only for observers in western North America. At 6:47 pm Pacific Time (in twilight), Io’s shadow will join Europa’s shadow already in progress. The two shadows will cross (at different Jovian latitudes) until 8 pm PDT, when Europa’s shadow will depart, leaving Io’s to complete its passage as Jupiter is setting.

Note that as long as Jupiter is above the horizon for them at the appointed time, everyone on Earth will see the same Jupiter events. If you are not in the Eastern time zone, add or subtract the correct number of hours for your own zone.

Due to Jupiter’s rapid 10-hour rotation period, the Great Red Spot (or GRS) is only observable from Earth every 2nd or 3rd night, and only during a predictable three-hour window. The GRS will be easiest to see using a medium-sized, or larger, aperture telescope on an evening of good seeing (steady air). If you’d like to see the Great Red Spot in your telescope, it will be crossing the planet tonight (Sunday evening) from dusk until 9:30 pm EDT, on Friday, October 18 from dusk to 9 pm EDT, and on Sunday, October 20, starting at 8 pm EDT.

Yellow-tinted Saturn is in the southern evening sky, too – but it is rather less bright than Jupiter. The ringed planet will be visible from dusk, when it will be about 2.5 fist diameters above the southern horizon, until almost 11 pm local time. Saturn’s position is just to the upper left (or celestial east) of the stars that form the teapot-shaped constellation of Sagittarius (the Archer) and about 2.5 fist diameters to the upper left (or celestial east) of Jupiter.

A look at Saturn is well worth dusting off your old telescope! Once the sky is dark, even a small telescope will show Saturn’s rings and several of its brighter moons, especially 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 right of Saturn tonight (Sunday) to the upper left of the planet next Sunday. (Remember that your telescope will flip the view around.)

The next planet in the line of evening planets, distant and dim, blue Neptune is visible all night long among the stars of eastern Aquarius (the Water-Bearer), and is less than a finger’s width to the right (or celestial west) of a medium-bright star named Phi (φ) Aquarii. Both blue Neptune and that golden-coloured star will appear together in the field of view of a backyard telescope at medium power. The distance between the star and the planet is steadily increasing due to Neptune’s westward retrograde orbital motion.

Blue-green Uranus will be rising in the east at 7 pm local time this week. It will remain visible all night long because it is only a couple of weeks ahead of its annual opposition date – when it will appear at its closest and brightest for 2019. The planet is sitting below (or to the celestial south of) the stars of Aries (the Ram) and is just a palm’s width above the circlet of stars that form the head of Cetus (the Whale). At magnitude 5.7, Uranus is actually bright enough to see in binoculars and small telescopes, under dark skies. You can use the three modest stars that form the top of the head of the whale (or sea-monster in some tales) to locate Uranus for the next several months – because the distant planet moves so slowly in its orbit.

Mars is now pulling away from the sun’s glare in the eastern pre-dawn sky. It rises at about 6:15 am local time and will become more easily visible later this month. Unfortunately, the red planet is on the far side of the sun from us – so it will remain rather small and faint until early next year.

Orionids Meteor Shower

We’ve finally entered meteor shower season! Over the next few months, we’ll experience a wave of several showers. The excellent Orionids Meteor Shower, which is derived from fine particles dropped by repeated past passages of Comet Halley, runs from September 23 to November 27, and is observable world-wide. The Orionids (for short) will build in intensity this week, and then peak in the hours between midnight and dawn (in your local time zone) on Tuesday, October 22. At that time, the sky overhead will be plowing through the densest region of the particle field, generating as many as 25 meteors per hour.

This shower has a broad period of activity because the debris field is very spread out because the comet’s orbit does not cross Earth’s at a sharp angle. So, technically, the Orionids will linger until late November – but will decrease in quantity as time passes.

The meteors can appear anywhere in the sky, but true Orionids will be travelling in a direction away from a location in the sky called the radiant. It’s positioned a fist’s diameter to the upper left of the bright red star Betelgeuse in the constellation of Orion, which gives this shower its name.

Although not too numerous, Orionids are known for being bright and fast-moving. Unfortunately, the waning half-illuminated moon will overwhelm the weaker meteors this year. You can watch for meteors before midnight, too – but many of them will be obscured by the Earth’s horizon.

To see the most meteors, get away from light-polluted urban skies and find a dark site with plenty of open sky. Don’t bother with binoculars or a telescope – their fields of view are too narrow for meteors. And don’t watch the sky near the radiant – those meteors will be travelling towards you and will produce very short streaks. Just keep your eyes on the sky overhead.

You can start watching as soon as it is dark, or head outside before the dawn twilight begins. Avoid bright white light from phones or tablets – it will spoil your eyes’ dark adaptation (red light is fine). If the peak night forecast calls for clouds, try the nights before or the nights after. Happy hunting!

Bright October Stars

Around its full phase, bright moonlight tends to overwhelm many of the medium-bright and dimmer stars. So let’s review some of the very bright stars you can see on any night this week.

It’s a good idea to learn the brightest stars, and this time of year, three of the brightest ones hug the horizon. Orange Arcturus is the brightest star in Boötes (the Ploughman). The eye-catching magnitude 0.15 star twinkles brightly, low in the western sky after sunset. It’s the fourth brightest star in the night sky, globally.

The white star Fomalhaut shines in Piscis Austrinus (the Southern Fish). Look for that star sitting low over the southern horizon. It never gets very high for Canadians, but it’s nearly overhead for observers at low latitudes. Fomalhaut is only the 18th brightest star, but dominates in its sparse celestial neighbourhood. It’s also the first star to have an exo-planet directly imaged!

In early evening, bright, yellow Capella sits low in the northeastern sky, ready to begin its nightly passage of the heavens. Sun-like Capella precedes the great starry ring of its constellation Auriga (the Charioteer) and is the sixth brightest star in the heavens.

Finally, the three bright, blue-white stars of the Summer Triangle, namely Deneb, Vega, and Altair, are still flying high overhead. Have you mastered these six stars? Good, because the bright beacons of winter are just around the corner!

Constellations and Asterisms

If you missed last week’s note about constellations and asterisms – I posted it with star charts here.

Public Astro-Themed Events

Every Monday evening, York University’s Allan I. Carswell Observatory runs an online star party – broadcasting views from four telescopes/cameras, answering viewer questions, and taking requests! Details are here. On Wednesday nights they offer free public viewing through their rooftop telescopes, including their brand new 1-metre telescope! If it’s cloudy, the astronomers give tours and presentations. Registration and details are here.

On Friday evening, October 18 at 8 pm, in the University of Toronto Mississauga’s William Davis Building, the Mississauga Centre of the RASC will hold their free public Speaker’s Night meeting. This one will feature RASC President Chris Gainor speaking about the Hubble Space Telescope’s rich history. Details are here.

The next RASC-hosted Night at the David Dunlap Observatory will be on Saturday, October 19. There will be sky tours in the Skylab planetarium room, space crafts, a tour of the giant 74” telescope, and viewing through the 74” and lawn telescopes (weather permitting). The doors will open at 8:30 pm for a 9 pm start. Attendance is by tickets only, available here. If you are a RASC Toronto Centre member and wish to help us at DDO in the future, please fill out the volunteer form here. And to join RASC Toronto Centre, visit this page.

This Fall and Winter, spend a Sunday afternoon in the other dome at the David Dunlap Observatory! On Sunday afternoon, October 20, from noon to 4 pm, join me in my Starlab Digital Planetarium for an interactive journey through the Universe at DDO. We’ll tour the night sky and see close-up views of galaxies, nebulas, and star clusters, view our Solar System’s planets and alien exo-planets, land on the moon, Mars – and the Sun, travel home to Earth from the edge of the Universe, hear indigenous starlore, and watch immersive fulldome movies! Ask me your burning questions, and see the answers in a planetarium setting – or sit back and soak it all in. Sessions run continuously between noon and 4 pm. Ticket-holders may arrive any time during the program. The program is suitable for ages 3 and older, and the Starlab planetarium is wheelchair accessible. For tickets, please use this link.

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