The Wolf Moon Wanders the Winter Heptagon and a Merry Perihelion has Night-time Planets, a Morning Comet, and Meteors!
This fantastic widefield composite image of the 2020 Quadrantids meteor shower over Flajšová, Oravská Lesná, Slovakia was captured by Czech astronomer Petr Horálek on the nights bracketing the peak of January 4.The radiant is out of frame to top left. That year, the star Betelgeuse in Orion (right of centre) was unusually dim. The glowing reddish arc of Barnard’s Loop is visible, too. Petr’s website hosts many more gorgeous images. It’s https://www.petrhoralek.com/
Merry Perihelion and Happy New Year, Stargazers!
Here are your Astronomy Skylights for the week of January 1st, 2023 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. To subscribe to these emails please click this MailChimp link.
If you’d like me to bring my Digital Starlab portable inflatable planetarium to your school or other daytime or evening event, or deliver a session online, contact me through AstroGeo.ca, and we’ll tour the Universe, or the Earth’s interior, together! My terrific book with John A. Read entitled 110 Things to See With a Telescope is a guide to viewing the deep sky objects in the Messier List – for both beginners and seasoned astronomers. DM me to order a signed copy!
The moon will flood night skies worldwide with light as it ramps up to its full phase on Friday. That will put a damper on the Quadrantids meteor shower and the pre-dawn comet C/2022 E3 (ZTF), so I’ve highlighted some lunar sights to enjoy. Earth reaches its closest point to Sol at mid-week, and the bright planets parade all evening. Read on for your Skylights!
Earth Closest to the Sun
Merry Perihelion! On Wednesday morning, January 4 at 16:00 Greenwich Mean Time, or 11 am EST and 8 am PST, the Earth will arrive at perihelion, its minimum distance from the sun for the year. At that time Earth will be 147.099 million km from our star – or 1.67% closer than our mean distance of 1.0 Astronomical Units (or 1.0 A.U.).
Earth’s distance from the sun varies throughout the year because our orbit is elliptical enough to varying the Earth-sun distance by 3.3%. We don’t feel warmer at perihelion. As winter-chilled Northern Hemisphere dwellers will attest, daily temperatures on Earth are not controlled by our proximity to the sun, but by the number of hours of daylight we experience, which is only about 9 hours at this time of the year in the Great Lakes region.
Quadrantids Meteor Shower Peak
Named for a now-defunct, northerly constellation called Quadrans Muralis (the Mural Quadrant), which used the stars in northern Boötes (the Herdsman), the Quadrantids meteor shower runs from December 30 to January 12 every year. This shower’s most intense period, when 50 to 100 meteors per hour can occur, lasts for only about 6 hours surrounding the peak. This shower occurs when the Earth traverses the densest part of a cloud of tiny particles in space that were deposited over time by the repeated passages of an asteroid designated 2003EH. When the particles strike our upper atmosphere at tremendous speed, they ionize the air molecules along a 1-metre wide zone that can stretch for kilometres – producing the streaks of light we see overhead as meteors. Quadrantids commonly produce bright fireballs because the stony particles are also burning up.
The peak will occur on Wednesday, January 4 at 3:00 GMT, which converts to 10 pm Eastern Time on Tuesday evening, January 3. At that time, the shower’s radiant, which lies beyond the tip of the Big Dipper’s handle, will be below the horizon – so the optimal time for viewing Quadrantids in the Americas will be from midnight to dawn on Wednesday, while the shower’s radiant will be climbing the northeastern sky. A bright gibbous moon will obscure the fainter meteors before it sets around 4:30 am local time. Meteor showers are usually worldwide events – but this one’s very northerly radiant will not climb above the horizon for observers in the Southern Hemisphere, reducing the numbers for them.
To see the most meteors, find a safe, wide-open, dark location, preferably away from light polluted skies, and just look up with your unaided eyes. The fields of view of binoculars and telescopes are too narrow to be useful for meteors. Don’t spend too much time watching the radiant because the meteors appearing near that location will be short – but do take note of whether they can be traced backwards to the radiant. Try not to look at your phone’s bright screen – it’ll ruin your night vision. Just keep your eyes heavenward – even while you are chatting with companions. Don’t forget to bundle up, and good luck!
Comet C/2022 E3 (ZTF) Update
In October, I shared updates on a comet named c/2022 E3 (ZTF) that is predicted to become bright enough to see in binoculars come February. In the past months it has grown enough to be visible in backyard telescopes under dark skies as a very faint fuzzy patch. The downside is that it is only observable in the pre-dawn hours now. By the end of January, it will become circumpolar and visible by midnight.
This week comet E3 ZTF will slowly fly northward through the constellation of Corona Borealis (the Northern Crown). The crown’s stars are situated in the lower third of the northeastern pre-dawn sky, with the keystone shape of Hercules positioned to the lower left and the very bright star Arcturus sparkling to the upper right.
At latitudes near Toronto, Corona Borealis’ stars will completely rise by 1:30 am – but the best time to see the comet will be 4-6 am in your local time zone, when it will be higher. The comet will not be too close to any convenient guideposts. On Monday morning, it will sit more or less between the stars Theta and Iota Coronae Borealis, just outside the imaginary circlet of stars. Over this week, the comet will shift farther from the circle, in the direction of Polaris.
The Moon
The moon will dominate the night sky worldwide this week. Its more than 85%-illuminated face will flood the sky with light during an after-dinner stroll in the chilly winter air or your down-under summer BBQ. Because the moon always stays within a palm’s width of the ecliptic – it echoes the sun’s behavior. January moons climb very high in the sky for mid-northern latitude sky-watchers and sit very low in the sky for those at mid-southern latitudes. Full moons during the winter months at mid-northern latitudes cast shadows similar to the summer noonday sun.
Today (Sunday) the waxing gibbous moon will rise after noon hour and cross the sky all afternoon. As dusk darkens the sky, the brightest stars of Aries (the Ram) will appear above it. For observers in the Americas, the moon will have just completed an occultation of the magnitude 5.7 planet Uranus. If you ever wanted to see Uranus, use binoculars or a backyard telescope to spot its bluish dot shining less than a lunar diameter to the moon’s right (or celestial west). In more westerly time zones, Uranus will be 3-4 lunar diameters from the moon. Observers in the Canadian Maritimes and eastward across Greenland, Iceland, most of northern Europe, and most of northern and western Russia can observe the occultation starting around 21:00 GMT.
On Monday the moon will shift east into Taurus (the Bull). The stars of the Pleiades cluster will shine just a few finger widths to the moon’s upper left (celestial north), but they’ll be awash with moonlight, so use binoculars to see them. That night, the curved, pole-to-pole terminator line that separates the lit and dark hemispheres will fall just west of Sinus Iridum, the Bay of Rainbows. That semi-circular feature, 249 km in diameter, is a large impact crater that has been flooded by the same dark-toned basalts that filled the much larger Mare Imbrium to its east – forming a round bay on the western edge of that mare. An effect nick-named the Golden Handle is produced when the low-angled sunlight along the terminator brightens the prominent Montes Jura mountain range surrounding Sinus Iridum on the north and west. Sinus Iridum is almost craterless, but hosts a set of northeasterly-oriented wrinkle ridges that are revealed at this phase. In a backyard telescope you can see how the mountains, actually the original crater rim, sink below the basalts, forming the promontories Laplace (the northern tip) and Heraclides (the southern tip).
In the eastern sky on Tuesday evening, the bright, waxing gibbous moon will be shining near prominent, red-tinted Mars. In the Americas, the moon will be positioned below (or celestial east of) Mars – close enough for them to share the view in binoculars. The pair will cross the sky together and set in the northwest before dawn. In the interim, the moon will drift farther from Mars and the diurnal rotation of the sky will lift the moon higher than the red planet. Around 20:00 GMT observers in most of southern and eastern Africa, Madagascar, and the Maldives can watch the moon cross in front of, or occult, Mars. Here’s a map showing where it’s visible. Use an astronomy app to find out your exact times.
From Tuesday to Friday the moon will cross through the Winter Football, also known as the Winter Hexagon and Winter Circle. The giant asterism is composed of the brightest stars in the constellations of Canis Major (the Big Dog), Orion (the Hunter), Taurus (the Bull), Auriga (the Charioteer), Gemini (the Twins), and Canis Minor (the Little Dog) – specifically the stars Sirius, Rigel, Aldebaran, Capella, Castor & Pollux, and Procyon. This winter, Mars’ position between Aldebaran and Capella will turn the shape into a heptagon! In contrast, the bright moon will spend the coming weekend among the faint stars of Cancer (the Crab).
On Friday, January 6 at 6:08 pm EST, 3:08 p.m. PST, or 23:08 GMT, the moon will reach its full phase. Full moons in January always shine in or near the stars of Gemini (the Twins) or Cancer (the Crab). Since they are, by definition, opposite the sun on this day of the lunar month, full moons are always fully illuminated – rising at sunset and setting at sunrise.
The moon has always shone down upon the denizens of Earth. At some point, people began to seek to understand our natural environment and to take advantage of the annual variations in the seasons in order to schedule planting, harvesting, hunting, and celebrations. Full moons naturally became celestial time keepers since they were obvious to everyone and conveniently rose at sunset. Moreover, the full moon’s bright light allowed people to be out and about safely at night. It lit the way of the hunter or traveler before modern conveniences like electric lights, and let workers in the fields devote extra hours to get the harvest in.
Each society around the world developed its own set of stories for the moon, and every month’s full moon now has one or more nick-names related to human spirit or the natural environment. The Indigenous Ojibwe people of the Great Lakes region call the January full moon Gichi-manidoo Giizis, the “Great Spirit Moon”. (You might recall that name from hearing or singing Henry Wadsworth Longfellow’s The Song of Hiawatha.) For them, January is a time to honour the silence, and recognize one’s place within all of Great Mystery’s creatures. The Mi’kmaw of the Canadian Maritimes use the name Punamjuiku’s, the “Tom Cod Spawning Moon”. You can learn more about the Mi’kmaw moons here.
The Algonquin of the Great Lakes call this full moon Squochee Kesos, the “Sun has not strength to thaw moon”. The Haida’s of western Canada and Alaska use Táan Kungáay, the “Bear Hunting Moon”. The Cree call the January full moon Opawahcikanasis, the “Frost Exploding Moon”, when trees crackle from the extreme cold temperatures. For Europeans, the January full moon is commonly known as the Wolf Moon, Old Moon, or Moon after Yule. The Wolf Moon name might also be derived from North American First Nations traditions, although some think it has an Anglo-Saxon origin. In either case, it’s likely that the hungry wolves calling to one another in the dead of winter would leave an impression on anyone before our modern era.
During this week, while the moon is close to being fully illuminated, the sunlight striking the moon will be coming from directly “behind you”, especially when you face the full moon. It’s analogous to the way the projector in the rear of a cinema lights up the movie screen in front of you. That sunlight is arriving straight-on to the moon’s surface, so it doesn’t generate any shadows. Every variation in brightness and colour you see on a full moon is due entirely to the moon’s geology, not its topography! At that time, you can easily distinguish the dark, grey, basalt rocks from the bright, white, aluminum-rich anorthosite rocks.
The basalts overlay the various lunar maria, Latin for “seas” – coined because people used to think they were water-filled. The maria are basins excavated by major impactors early in the moon’s geologic history and later flooded with molten rock that upwelled from the interior of the moon late in the moon’s geological history. That filling happened in stages. A backyard telescope will easily reveal terraces of lava that “froze” after each incursion – but those are best seen when the moon isn’t full.
The much older and brighter parts of the moon are composed of anorthosite rock. Those areas are higher in elevation and are also heavily cratered – because there has been no wind and water, or plate tectonics, to erase the scars of countless impacts. By the way, the bright, white appearance of anorthosite is produced by sunlight reflecting off of the crystals the rock is made of – the same sort of crystals you see in the granite countertops in Earth’s kitchens. And yes, there are coloured rocks on the moon.
Some of the violent impacts that created the craters in the highland regions also spread bright streams of ejected material long distances, some landing on top of the darker maria. We call those streaks lunar rays systems. Some rays are thousands of km in length – like the ones from the very bright 100 million-year-old crater Tycho in the moon’s south central region.
Use your binoculars to scan around the moon this week. There are large and small ray systems everywhere! There are also places where craters recently blasted into the maria have made dark basalt rays on the white rocks. And, since the dark basalt overlays the white, older rock underneath it, a small telescope will show lots of craters where a hole has been punched through the basalt, producing a white-bottomed crater!
Several of the maria link together to form a curving chain across the northern half of the moon’s near-side. Mare Tranquillitatis the “Sea of Serenity”, where humankind first walked upon the moon, is the large, round mare in the centre of the chain. Sharp-eyes might detect that this mare is darker and bluer than the others, due to enrichment of the basalt by the metal titanium. That’s one of the reasons why Apollo 11 was sent there. Earth-bound telescopes – even the largest ones – cannot see the items left by the astronauts on the moon. When the air is particularly steady, the smallest feature you can see on the moon with your backyard telescope is about 2 to 6 km across – far larger than any lunar module descent stage, which are only about 4 metres across. Only cameras on spacecraft in orbit around the moon can photograph the Apollo astronauts’ footprints, lunar rover tracks, and equipment. The upcoming Artemis missions to the moon will focus on the polar regions where water frozen in permanently shadowed craters can be harvested.
Now that you know more of the lunar terminology, here are some additional things to watch for…
While the moon is almost fully illuminated, you can use your telescope to look at the dark stains left behind by extinct volcanoes on the moon! Alphonsus is a 110 km wide crater located just south of the moon’s centre, on the upper right shore of Mare Nubium. Any size of telescope will reveal a triangle formed by dark spots on the crater’s floor near its left and right rims. Those are ash deposits. Another crater with similar features is Atlas, which sits in the northern region of the moon, about halfway between the northern shore of Mare Serenitatis and the edge of the moon.
This week will also be ideal for viewing the prominent crater Copernicus in eastern Oceanus Procellarum, the “Ocean of Storms”, which is the large dark region located south of large Mare Imbrium. Copernicus is located slightly to the upper left (lunar northwest) of the moon’s centre. The Jesuit priest Giovanni Battista Riccioli, who published a labelled map of the moon in 1651, deliberately placed the craters named for astronomers Nicolaus Copernicus and Johannes Kepler, their defender Ismaël Bullialdus, and the Greek philosophers Aristarchus, Eratosthenes, and Seleucus, into the Ocean of Storms because they all dared to suggest that Earth revolved around the sun – in contravention to the church’s teachings. Riccioli honoured his fellow Jesuits Grimaldi and Clavius with prominent craters elsewhere on the moon.
The 800 million year old crater Copernicus is visible with unaided eyes and binoculars – but telescope views will reveal many more interesting aspects of lunar geology. Several nights before and after the moon reaches its full phase, Copernicus will exhibit heavily terraced edges (due to slumping), an extensive ejecta blanket outside the crater rim, a complex central peak, and both smooth and rough terrain on the crater’s floor. Around full moon, Copernicus’ rather ragged ray system, which extends 800 km in all directions, becomes prominent. Use high magnification to look around Copernicus for small craters with bright floors and black haloes – caused by impacts through Copernicus’ white ejecta that excavated dark Oceanus Procellarum basalt and even deeper highlands anorthosite.
The prominent crater Kepler, located to the lunar west of Copernicus, will be illuminated from Monday onward. Smaller, but brighter Aristarchus, which is positioned north of them, will be visible starting on Tuesday. It is one of the most colourful regions on the moon. NASA orbiters have detected high levels of radioactive radon at Aristarchus.
The Reiner Gamma Lunar Swirl is a small, high-albedo (i.e., light in colour) area located just inside the western edge of Procellarum. It’s above (due north) of the dark, round crater Grimaldi and to the left (due west) of Kepler. The swirl is best seen a night or two after the moon’s full phase. The small, but prominent 30 km diameter crater named Reiner is located a short hop to the right (east-southeast) of Reiner Gamma. The swirl is composed of ancient lunar basalt that has not been darkened by weathering, likely due to protection from cosmic rays by a strong localized magnetic field – the swirl has one of the strongest magnetic anomalies on the moon! At high magnification, its complex, fish-like shape is fascinating. Take a look!
The Planets
During the first days of this week, lucky observers with an unobstructed, cloud-free sky to the southwest at dusk can continue to see the moon plus every bright planet in the sky at the same time! The very bright dot of Venus will be easily spotted just above the southwestern horizon after sunset. 170 times fainter Mercury will challenge you at Venus’ lower right (or celestial west). Today (Sunday) Mercury will be positioned a palm’s width from Venus. Then it will drop sunward on each subsequent day. Observers at tropical latitudes, where its orbit will intersect the horizon more vertically, will have an easier time finding Mercury.
Be sure to wait until the sun has completely disappeared before searching for those planets in binoculars or telescopes. Venus will show a 95%-illuminated disk in your telescope, but clear views will not be possible through so much intervening air. Venus is swinging away from the sun and climbing higher each evening, so we’ll enjoy clear views of it each week.
The rest of the bright planets will form a 130 degrees-long arc across the sky from Venus in the west to Mars in the east, tracing out the plane of our solar system. Uranus, Neptune, and a couple of major asteroids will be strung between them.
By the time that Venus sets, after about 6:15 pm local time, the yellowish dot of Saturn will become visible in the lower part of the southwestern sky. Our window of opportunity to enjoy Saturn is closing. Take a look at the magnitude 0.8 planet as soon as you can find it in your telescope. It, too will look less crisp as it drops into the thicker air. This week, Saturn will set at about 8 pm local time. Saturn will be shining just to the right (celestial north) of the medium-bright tail stars of Capricornus (the Sea-Goat), Deneb Algedi on the upper left (celestial east) and Nashira on the lower right (celestial west). Over the next two weeks, you’ll be able to use binoculars or your sharp eyesight to see Saturn’s easterly prograde motion shift the planet past them. I plotted Saturn’s long-term path here.
On a night with steady air, quality 10×42 binoculars (and larger) should show Saturn and its rings as a tiny, tilted oval. Even a small telescope can show the planet’s subtly banded globe encircled by its glorious rings. See if you can make out the Cassini Division, a narrow, dark gap that separates Saturn’s main inner ring (named B) from its bright outer ring (named A). A small telescope can also pick up several of Saturn’s moons – especially its largest, brightest moon, Titan! From here on Earth, Saturn’s axial tilt of 26.7° lets us see the top of its ring plane, and allows its brighter moons to array themselves all around the planet. (In contrast with Saturn, Jupiter’s axis is only tilted by 3°, so Jupiter’s moons show in a line running through that planet’s equator.)
Titan never wanders more than five times the width of Saturn’s rings from the planet. The much fainter moon named Iapetus can stray up to twelve times the rings’ width during its 80-day orbit of Saturn. The next brightest moons Rhea, Dione, Tethys, Enceladus, and Mimas all stay within one ring-width of Saturn. During evening this week, Titan will migrate counter-clockwise around Saturn, moving from the left (or celestial east) of Saturn tonight (Sunday) to the lower right (or celestial west) of Saturn next Sunday. (Remember that your telescope might flip that view around.) How many of the moons can you see in your telescope?
The bright white dot of magnitude -2.4 Jupiter, one-fourth as bright as Venus, but still 19 times brighter than Saturn, will pop into view in the southern sky well before Venus sets. Once the sky has fully darkened, look for the faint stars of Pisces (the Fishes) just above Jupiter. The bright corner stars of the Great Square of Pegasus will sparkle higher still.
Your binoculars should be able to show Jupiter as a small disk bracketed by its line of four Galilean moons named Io, Europa, Ganymede, and Callisto. Those moons complete orbits of the planet every 1.7, 3.6, 7.2, and 16.7 days, respectively. If you see fewer than four moons, then one or more of them is crossing in front of or behind Jupiter, or hiding in Jupiter’s dark shadow – or two of the moons are very close together or occulting one another. The moons’ arrangement varies each night. On Friday night all four moons will once again form a conga line to the west of Jupiter!
Jupiter will look best in a telescope when it is highest due south around 5:30 pm. It will set in the west around 11:30 pm local time. Even a small, but decent quality telescope can show you Jupiter’s dark belts and light bands, which are aligned parallel to its equator. With a better grade of optics, Jupiter’s Great Red Spot, a cyclonic storm that has raged for hundreds of years, becomes visible for several hours when it crosses the planet every 2nd or 3rd night. For observers in the Americas, that GRS will cross Jupiter’s disk in early evening on Tuesday, Thursday, and Saturday, and late on Monday, Wednesday, and Saturday evening. If you have any coloured filters or nebula filters for your telescope, try enhancing the spot with them.
The round, black shadows of Jupiter’s Galilean moons are visible through a good backyard telescope when they cross the planet’s disk. On Monday evening, January 2 the small shadow of Io will cross the equator of the planet, from 6:25 pm to 8:30 pm EST. The GRS will accompany it for the send half of the trip. While you are watching, note that the moon Ganymede, which will be hidden in Jupiter’s shadow to the east of Jupiter, will pop into view at about 8:12 pm EST. On Thursday evening, Europa’s tiny shadow will cross with the GRS from 4:57 pm to 6: 18 pm EST. The events are visible over a wide region. Don’t forget to adjust these quoted times into your own time zone.
On Friday evening, January 6, observers with telescopes in southern and eastern Asia and south to western Australia can watch two shadows slide across at the same time! At 7:50 pm Indochina Time (00:50 GMT), the large shadow of Ganymede will begin to cross Jupiter’s southern hemisphere, joining Io’s smaller shadow, which began its own passage across Jupiter’s equatorial zone at 7:22 pm ICT (00:22 GMT). 102 minutes later, at 9:32 pm ICT (02:32 GMT), Io’s shadow will leave the planet. Ganymede’s shadow will complete its own transit 10:20 pm ICT (03:20 GMT). These times will vary by a few minutes depending on your location.
In mid-evening this week, magnitude 7.9 Neptune will be located a slim fist’s width to the lower right (or 8.5° to the celestial west-southwest) of Jupiter, about half way towards the medium-bright star Hydor (Lambda Aquarii). Neptune’s apparent disk size is 2.3 arc-seconds (17 times smaller than Jupiter’s). Try to view Neptune while it is highest, right after dusk. The large asteroids designated (4) Vesta and (3) Juno are currently following Jupiter. They are near the eastern knee star of Aquarius (the Water-Bearer), named Psi1 Aquarii.
The bright red dot of magnitude -1.2 Mars will continue to be visible all night long. It will catch your eye in the eastern sky during evening, climb very high in the south around 10 pm local time (its best telescope viewing time), and then descend westward, allowing early risers to spot it above the western horizon before dawn. Mars continues to be positioned above the very bright, reddish star Aldebaran, which marks the angry eye of Taurus (the Bull) and to the lower left of the Pleiades star cluster. Mars will travel towards the Pleiades until mid-January.
In backyard telescopes this week, Mars will show an apparent disk diameter of 14 arc-seconds (Jupiter’s disk spans about 42 arc-seconds and the full moon is 1,800 arc-seconds wide). Mars’ Earth-facing hemisphere this week will display its bright northern polar cap – visible as a small bright spot along the planet’s edge, and some dark regions. To identify them, you can use a terrific Mars mapping tool created by Ade Ashford at http://www.nightskies.net/skyguide/mars/mars.html. Use the drop-down menu to select from two views of Mars, labelled or not. Mars takes about 20 minutes longer than Earth to rotate once fully on its axis. So viewing the planet at the same time on consecutive nights will show roughly the same view of it – but with its surface markings shifted by about 5°. If you have coloured filters for your telescope, see if the blue, orange, or red one improves the view.
The distant blue-green planet Uranus is located about 35% of the way from Mars towards Jupiter, and about 1.5 fist widths to the upper right (or 15° to the celestial west-southwest) of the Pleiades star cluster. Closer guideposts to Uranus are several medium-bright stars, including Botein (or Delta Arietis), Al Butain II (or Rho Arietis), and Sigma Arietis, which will appear several finger widths from the planet. Those stars mark the feet of the Aries (the Ram). Magnitude 5.7 Uranus will already be high enough for telescope-viewing, in the middle part of the eastern sky, after dusk this week. It will climb to its highest point in the southern sky just before 9 pm local time. Don’t forget to catch the lunar occultation of Uranus that I described above – if you live where it will be visible.
Watch Medusa’s Eye Pulsate
On early January evenings the constellation of Perseus (the Hero) is located high in the eastern sky. The easiest way to identify the constellation is to look for Perseus’ brightest star Mirfak, which shines midway between the W-shape of Cassiopeia (the Queen) and the even brighter, yellowish star Capella in Auriga (the Charioteer) below it.
The second brightest star of Perseus (the Hero) is Beta Persei (β Per), better known as Algol, from the Arabic Ra’s al-Ghul, which means “the Demon’s Head”. Algol represents the pulsing eye of Medusa the Gorgon, whose severed head Perseus is carrying. The star represented the god Horus in Egyptian mythology and was Rosh ha Satan “Satan’s Head” in Hebrew.
There’s a good reason for these scary associations. Ancient sky-watchers noticed that Algol is variable. Like clockwork, this star’s visual brightness dims noticeably once every 2 days, 20 hours, and 49 minutes. That happens because a dim companion star orbiting nearly edge-on to Earth crosses behind the much brighter main star. Once the eclipse begins, the light we see steadily drops in brightness for five hours. Then it ramps up again during another five hours – until the eclipse is over. Algol is the archetype for all eclipsing binary star systems, and is among the most accessible variable stars for beginner skywatchers.
The easiest way to monitor Algol’s variability is to note how bright that star looks compared to other, non-varying stars near it. When it isn’t dimmed, Algol shines at magnitude 2.1, similar in brightness to Almach, the bright star located a fist’s diameter above Algol (or celestial west) in Andromeda (the Princess). While dimmed, Algol shines at magnitude 3.4, about the same brightness as the star Gorgonea Tertia (or Rho Persei) located two finger widths to Algol’s right (or celestial south). Use your unaided eyes or binoculars to compare them.
On Wednesday, January 4 at 7:25 pm EST, Algol will be dimmed to its minimum brightness. Five hours later, at 12:25 am EST on Thursday, it will have returned to full brightness. By then it will be positioned halfway down the northwestern sky.
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. They host in-person viewing on the first clear Wednesday night each month. On Wednesdays they stream views online via the observatory YouTube channel. Details are here.
On Wednesday evening, January 4 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, building a backyard observatory, and photographing nebulae. Details are here.
My free, family-friendly Insider’s Guide to the Galaxy webcast with Samantha Jewett of RASC National returns on Tuesday, January 17 at 3:30 pm EST. We’ll select a fun topic in astronomy, and we’ll highlight the next batch of RASC’s Finest NGC objects. You can find more details and the schedule of future sessions here.
Keep looking up, and enjoy the sky when you do. I love questions and requests. Send me some!