The Full Grain Moon, Comet Zinner Zips towards Capella, and Mercury’s Best Manifestation for the year!

Star Walk
7 min readAug 28, 2018


(Above: Watson of Toronto took this detailed image of the full moon on February 22, 2016 when it was only 9 hours past full — the same situation we’ll see tonight, Sunday, August 26, 2018. Notice the strip of shadowed craters along the moon’s right-hand limb — proof that the moon has started to wane. Michael’s lunar images are here.)

A Binocular Comet

This fall, astronomers are watching for two comets that are predicted to brighten enough to see with binoculars and possibly even your unaided eyes. I’m going to continue updating you about them, even though, like cats, comets have tails and are extremely prone to doing their own thing, despite what we might want them to do.

(Above: The path of Comet 21P/Giacobini-Zinner in the northeastern sky this week, shown here at 11 pm local time. )

Comet 21P/Giacobini-Zinner returns to our vicinity every 6.5 years — hence the “P” for “periodic” in its designation. It has been gradually brightening because it is approaching Earth’s orbit. Later this week, once the bright, full moonlight wanes, you should be able to see the faint fuzzy greenish object in binoculars or a small telescope, if you can escape city lights.

The comet is located in the north-northeastern sky on a track that moves it downwards every night. Tonight (Sunday) it will be found about a fist’s diameter (11°) to the left of the bright star Mirfak in Perseus (the Hero). Next Sunday, it will have descended to land only a finger’s width to the upper right of the very bright star Capella in Auriga (the Charioteer); putting the two objects inside the field of view of a low magnification telescope. Capella will still be fairly low at 11 pm local time, but the comet and star will be carried higher during the course of the night due to Earth’s rotation.

A second comet named 46P/Wirtanen is predicted to become much brighter by December. Right now, it is tickling the belly of the whale (Cetus), but it’s far too dim to look for yet.

The Moon and Planets

August’s full moon, known as the “Sturgeon Moon”, “Red Moon”, “Green Corn Moon”, and “Grain Moon” occurred this morning (Sunday). The Assiniboine People called the August full moon the Black Cherries Moon, and the Inuit call it the Swan Flight Moon. In China, it’s the Harvest Moon and in India it’s Bhadrapad Purnima. This one will shine within the constellation of Aquarius (the Water-Bearer), but you’ll be hard-pressed to see the dim stars of that modest constellations due to so much bright moonlight. When the moon rises on Sunday evening, it will appear a hair less than full. Binoculars or a telescope will reveal a narrow strip of shadowed terrain along the moon’s right (its eastern) edge.

For the rest of this week, the waning moon will continue to slide eastward through more water constellations, including Cetus (the Whale) and Pisces (the Fishes). It will also rise later and later, and then linger into the morning sky for your commute to school(!) or work.

When the waning crescent moon rises at midnight on Sunday, September 2, it will be sitting only two finger widths to the lower left of Aldebaran, the brightest star in Taurus (the Bull). The moon and bright star will cross the sky together while the moon’s eastward orbital motion will slowly draw them apart. Two hours earlier, at 9:50 pm EDT (01:50 UT), observers in Greenland and northernmost Canada will see the moon cross in front of, or occult, Aldebaran.

(Above: Mercury shown at 6 am local time, one day past its greatest elongation west of the sun. the steep Ecliptic (yellow line) causes the planet to rise well before the sun, facilitating our observations.)

For people who live in the GTA and mid-northern latitudes around the world, Mercury will be very easy to see in the eastern pre-dawn sky this week. Today (Sunday), Mercury will reach an angle of 18 degrees west of the Sun, its widest separation for this appearance. That means it will rise in the east well before the sun, in a somewhat darker sky. You’ll be able to see it between about 5:15 and 6 am local time all week. Try to pick a spot with a low and uncluttered eastern horizon.

Extremely bright Venus is quickly descending the western early evening sky each evening as its orbit carries it back towards the sun. Tonight it will set at about 9:30 pm local time, but a week from now that will advance to 9 pm. Meanwhile, the bright planet will appear to be approaching the bright star Spica in Virgo (the Maiden). The effect is caused by Earth’s motion carrying the entire sky westward faster than Venus is moving. They’ll “kiss” this Friday and Saturday evening; a gorgeous sight in binoculars! In a small telescope, Venus’ disk will resemble a first quarter moon, half-lit on the sunward side (although your telescope might flip the view). The planet will also be growing larger in apparent diameter because it is travelling towards the Earth right now.

(Above: The early evening sky, shown here Sunday evening at 9 pm local time, features the naked-eye planets Venus, Jupiter, Saturn, and Mars.)

We are in the closing chapter for observing Jupiter this year. The earlier sunsets will buy us some extra evening observing time, but its position low in the sky will add a great deal of extra blurring atmosphere between it and our telescopes. This week, the very bright planet will emerge from the southwestern twilight soon after dusk, and then set in the west-southwest after about 10:30 pm local time. Jupiter, which has been slowly shifting eastwards, will continue to pull away from the nearby bright star Zubenelgenubi, the brightest star in Libra (the Scales). In binoculars, you’ll plainly see that Zubenelgenubi is a pair of stars. While you have the binoculars handy, see if you can see Jupiter’s four Galilean moons (Io, Europa, Callisto, and Ganymede) flanking the planet.

The Great Red Spot (or GRS, for short) takes about three hours to cross Jupiter’s disk. But the planet’s 10-hour rotation period (i.e., its day) means that the spot is only observable from Earth every 2–3 nights. If you’d like to see the GRS, use a medium-sized telescope (or larger). You’ll have your best luck on evenings with steady air — when the stars are not twinkling too much. Try to look within an hour before or after the following times: Sunday, August 19 at 9:46 pm (as the planet is setting), Wednesday, August 29 at 8:07 pm (starting in twilight), and Friday, August 31 at 9:46 pm (as the planet is setting). All times are given in Eastern Daylight Time (EDT), so adjust for your local time zone.

Medium-bright and yellow-tinted Saturn will appear not too high up the darkening southern sky shortly after dusk this week. The planet will reach its highest elevation of about 2 fist diameters above the southern horizon at around 9 pm local time, and then descend to set in the west by about 1:30 am. This summer, the ringed planet has been 4 finger widths to the upper right of the “lid” star of the Teapot in Sagittarius (the Archer). As the sky darkens, even a small telescope should be able to show you some of Saturn’s larger moons, especially Titan. Using a clock’s dial analogy, Titan will move counter-clockwise this week from a position at 2 o’clock (left of the planet) to 8 o’clock (right of the planet). (Remember that your telescope might flip and/or invert the view. Use the moon to find out how your telescope changes things.)

Mars will still be very bright this week. Visually, it will appear pink or orange due to the global dust storm it has experienced recently. Mars will rise over the southeastern horizon at around 7 pm local time (give or take, depending on your latitude) and then climb higher until 11 pm local time, when it will reach an elevation of about 20° (or two outstretched fist diameters) above the southern horizon. (That will be the best hour to view the planet in a telescope because it will then be shining through the least amount of Earth’s distorting atmosphere.) Note that 20° is lower than many trees and buildings, so a clear southern vista is essential. It will set in the west at around 3 am.

(Above: The ice giant planets Uranus and Neptune rise late and remain in view all night, as shown here at 10:30 pm local time this week.)

At visual magnitude 5.8, blue-green coloured Uranus is visible from late evening until dawn. You can see it without optical aid under very dark skies, or in binoculars and telescopes under moderately light-polluted skies. The ice giant planet is located in the eastern sky, about 4.5 finger widths to the left of the modestly bright star Torcular (Omega Piscium), which is above the “V” where the two starry cords of Pisces (the Fishes) meet.

Using a decent quality telescope you can also see the distant and very blue planet Neptune among the dim stars of Aquarius (the Water-bearer). It will rise in the east shortly before 8:30 pm local time. Look for the magnitude 7.8 planet sitting 1.75 finger widths to the right of the modestly bright star Phi (φ) Aquarii and 4 finger widths to the left of the brighter star Hydor (Lambda Aquarii).

Astronomy Skylights for this week (from August 26th, 2018) by Chris Vaughan.

Keep looking up to enjoy the sky! I love getting questions so, if you have any, send me a note.



Star Walk

Point your device at the sky and see what stars, constellations, and satellites you are looking at 🌌✨