Skylights: August 2022

August brings some welcome changes for skywatching: nights are getting longer and cooler, and for the first time in nearly six months, we have bright planets in our evening sky, as both Saturn and Jupiter are visible before midnight.

The number of hours of darkness noticeably increases through August, with the last 8pm sunset occuring on the 4th. The Sun will set before 8pm until May 17, 2023. The last 6am sunrise occurs on the 20th, and the Sun continues to rise later than this time until March 14, 2023.

The waxing crescent Moon appears just 4° north of Spica on the 3rd, and reaches its first quarter phase on the 5th. At moonset on the 7th, the waxing gibbous is just 4° to the right of Antares in Scorpius.

The Full Sturgeon Moon occurs on the 11th, when it will pass 4.3° south of Saturn, in Capricornus. It is evident that the Moon lies south of the ecliptic by its position relative to Saturn.

The waning gibbous Moon rises at the same time as Jupiter, about 9:30pm, on the 14th. After midnight, the Moon passes just 2.5° south of Jupiter.

The last quarter Moon occults Uranus at 11:40am on the 18th.As this is a daytime event, it will require specialized equipment and skill to observe the event. However, before dawn, you can see Uranus 2.5° east of the Moon.

On the 19th, the Moon passes between Mars and the Pleiades cluster in Taurus. On the 25th, it is 4.2° from the Beehive cluster, M44, in Cancer, 6.6° above Venus, and 3.7° west of dwarf planet Ceres.

An opportunity to spot the very old 28.7-day Moon occurs on the 26th, when the 0.9% illuminated crescent rises an hour before the Sun, and is visible 6° northeast of Venus. 

The Moon becomes new on the 27th, and returns to the evening sky near Mercury on the 28th and 29th. On the 30th, the beautifully illuminated crescent Moon with visible Earthshine will be just 5° from Spica in Virgo.

Mercury is in the evening sky all month, reaching its greatest elongation of 27° on the 27th, but unfortunately this will be a “low” apparition of the innermost planet due to the shallow angle of the ecliptic with respect to the western horizon during evening hours this time of year. At no time during August will Mercury be visible more than 55 minutes after sunset.

You may spot Mercury just 0.9° north of Regulus on the 3rd. The one-day-old waxing crescent is 10° to the right of Mercury on the 28th, and a day later, it is 5.5° above it.

Venus is in Gemini in early August, and is beginning to rise noticeably later with each passing morning. On the 2nd, it rises just before 4:00am, but by the 8th, it rises more than 10 minutes later. By the end of the month, it will rise at about 5:00am. Venus crosses the ecliptic, heading north, on the 2nd, and passes just 1° north of planetary nebula NGC 2392 (Caldwell 39) on the 4th. Venus is 6.5° S of Pollux on the 6th.

Venus forms a line with the Gemini twins Pollux and Castor on the 11th, and, after crossing into Cancer, shines brilliantly on the outskirts of the Beehive Cluster, M44, on the 17th and 18th.

With Venus now over 1.5 AU away, and with diminishing apparent elongation from the Sun, it shows an indistinct gibbous phase, just over 10 arcseconds in a telescope. 

Mars begins the month in Aries, and now rises before midnight. Mars is just 1.3° north of Uranus on the 2nd, making our solar system’s 7th planet easy to find with binoculars or a small telescope. The color contrast between ruddy Mars and teal Uranus can be quite striking in a telescope. Mars is over 170x brighter than Uranus. At 19.82 AU from Earth, Uranus is 17x farther away than Mars, at 1.13 AU. Mars shows an 8.4 arcsecond disk compared to Uranus’ 3.6”.

Beginning during the second week of August, Mars begins to pass near the Pleiades cluster in Taurus, and towards the end of the month, passes near the Hyades cluster. On the 30th and 31st, it lies along the line between Aldebaran and the Pleiades. 

Mars reaches its western quadrature point, 90° west of the Sun, on the 27th, and now shines at magnitude 0 and shows a gibbous disk nearly 10 arcseconds across. 

Jupiter, in Cetus, rises just after 10:30pm in early August, and 8:30pm at the end of the month. When the Moon is out of view, Jupiter is the most prominent object during the dark hours, until Venus rises at the beginning of twilight. As we approach Jupiter’s opposition next month, the giant planet is just over 4 AU away, and shows a staggeringly large 48 arcsecond disk. Its disk should even be evident in binoculars, and even the smallest telescopes will show some of its cloud features. 

Jupiter’s easiest-to-observe feature though, is not on the planet itself, but its four large Galilean moons. They shine at magnitude 6, can be seen in binoculars, and their changing positions can be seen on a nightly, and sometimes even hourly basis. Its moons Io, Europa, Ganymede, and Callisto complete orbits of Jupiter in 1.8 days, 3.5 days, 7,2 days, and 16.7 days, respectively.

Saturn reaches opposition on August 14, and now rises during evening twilight, in Capricornus. Like Jupiter, Saturn has a number of moons that can be observed with a telescope. Titan, the largest moon, orbits Saturn once every 16 days (just a day shorter than Jupiter’s Callisto) and at magnitude 8.5 can be seen with small telescopes. Saturn has a number of smaller moons that can be seen with an 8-inch telescope. These include Tethys, Dione, Rhea. Saturn’s outermost mid-sized Moon, Iapetus, can also be observed fairly easily with a 6-inch telescope, but it is easier to observe only when it is to the west of Saturn. This is due to its leading hemisphere being darker than its trailing hemisphere, resulting in its trailing hemisphere being brighter by about 2 magnitudes. Iapetus is at its brightest when it is near its maximum western elongation with respect to Saturn, which occurs on August 8, when Iapetus is 9.4 arcminutes from Saturn. Its best visibility occurs within a week on either side of this, and happens once during its 79-day orbit. The next best opportunity to observe Iapetus at its brightest occurs during the second half of October.

Uranus, in Aries, reaches its western quadrature point on the 11th. The seventh planet has moved a bit farther east since last year, and can now be found about a degree west of the midway point of a line connecting Bharani (41 Arietis) and Omicron Tauri. However, Uranus is now getting close enough to the Pleiades cluster that it is  becoming easy to use that object as a starting point. About 9° southwest of the Pleiades, you will find 4th magnitude Botein (Delta Arietis). From this star, Uranus is just 3° to the south-southwest, and forms the end of a shallow zig zag line with 6th magnitude stars 53 and 54 Arietis in between. Uranus is slightly brighter than these stars, and its small positional change with respect to them should make it stand out.

Neptune crosses the border from Pisces into Aquarius on the 12th, and is about 5° south of the eastern edge of the Circlet asterism, and ¼ of the way along a line between Jupiter and Saturn.. At magnitude 7.8, Neptune is visible in telescopes and binoculars, and lies at a distance of 29.17 AU.

Dwarf planet Pluto is well-placed for viewing, having reached opposition last month. Its magnitude 14.3 glow can be found, with a large telescope, just over 2° west-southwest of globular cluster M75 in Sagittarius.

Asteroid 4 Vesta, shining at magnitude 6.1, is moving west-southwestward in southern Aquarius, and reaches its opposition on the 14th. Throughout much of August, Vesta makes the apex of a shallow isosceles triangle with Fomalhaut and Saturn as the base. On the 8th, it is just 2.5° north of planetary nebula NGC 7293 (Caldwell 63).

Asteroid 3 Juno, at 1.5 AU away, shines at magnitude 8.6 in Pisces. In early August, it is just 2° south of magnitude 3.7 Gamma Piscium, the westernmost star of the Circlet asterism. It continues moving south-southwest, approximately in a line towards Lambda Aquarii.

Early August features the annual Perseids meteor shower. Although the shower peaks on August 11-12, it is actually active for several weeks, from late July through the third week of August. It can often be productive in the days leading up to the peak, which this year coincides with a Full Moon, so early August and a few days past peak present the better opportunities to see some.

Comet C/2017 K2 PanSTARRS continues to move southward from Ophiuchus into Scorpius. In early August it passes 2.5° east of the globular cluster M107. Later in the month, it enters the claws of Scorpius, passing within a degree of Acrab (Beta Scorpius) on the 23rd, and Dschubba (Delta Scorpii) on the 31st. The comet is expected to continue shining at about 8th magnitude.

You’ve probably heard a lot about the Dog Days the past few weeks, as it tends to be a phrase thrown about when the weather gets unpleasantly hot and humid, but the fact is that the Dog Days are not a meteorological phenomenon, but an astronomical one. The phrase references when the Dog Star, Sirius, begins to appear in the dawn sky. At our latitude, this occurs around the second week of August. You’ll need a clear southwestern horizon free of fog or haze. Try observing every morning until you see it. How early can you spot Sirius? By the 15th it should be visible, and each subsequent morning it will become higher and easier to see. Note that Sirius is the last star in the Winter Hexagon to rise, and although the weather may be warm now, we’re reminded by the stars that the cooler weather is not far away..