Night sky guide for August 2018: Partial solar eclipse, Perseid meteor shower

A partial solar eclipse will take place from 06:40 to 12:38 UTC on August 11. It will be visible in parts of northeast Canada, Greenland, extreme northern Europe, and northern and eastern Asia. It will be best seen in northern Russia with 68% coverage. 

At 09:59 UTC on the same day, the Moon will reach its new phase, making August 11 the best day of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere. At new moon, the Earth, Moon and Sun all lie in a roughly straight line, with the Moon in the middle, appearing in front of the Sun's glare.

The peak of the best meteor shower of this year – Perseids – is less than two weeks away. The thin crescent moon will set early in the evening leaving dark skies for what should be an excellent show. The Perseids are famous for producing a large number of bright meteors.  

The Moon will reach its full phase at 11:58 UTC on August 26. It will be visible from all latitudes north of 67°N. Its distance from the Earth will be 402 000 km (250 000 miles).

• August 11 – New Moon – 09:59 UTC. The Moon will be located on the same side of the Earth as the Sun and will not be visible in the night sky. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere. At new moon, the Earth, Moon and Sun all lie in a roughly straight line, with the Moon in the middle, appearing in front of the Sun's glare. In this configuration, we see almost exactly the opposite half of the Moon to that which is illuminated by the Sun, making it doubly unobservable because the side we see is unilluminated.

• August 11 – Partial solar eclipse – 06:40 – 12:38 UTC. A partial solar eclipse occurs when the Moon covers only a part of the Sun, sometimes resembling a bite taken out of a cookie. The eclipse will be visible in parts of northeast Canada, Greenland, extreme northern Europe, and northern and eastern Asia. It will be best seen in northern Russia with 68% coverage. 

• August 12, 13 – Perseid meteor shower. This is one of the best meteor showers to observe, producing up to 80 meteors per hour at its peak. It is produced by comet Swift-Tuttle, which was discovered in 1862. The Perseids are famous for producing a large number of bright meteors. The shower runs annually from July 17 to August 24 and peaks this year on the night of August 12 and the morning of August 13. The thin crescent moon will set early in the evening leaving dark skies for what should be an excellent show. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Perseus, but can appear anywhere in the sky. According to meteor expert Bill Cooke, they'll be the best shower of the year. The peak will be visible both the nights of August 11 – 12 and August 12 – 13, Cooke said, but he's inclined this year to lean toward the night of August 12 – 13 for the better show.

• August 13 – 48P/Johnson at perihelion. Comet 48P/Johnson will make its closest approach to the Sun, at a distance of 2.01 AU.

• August 14 – Conjunction of the Moon and Venus – 13:35 UTC. The Moon and Venus will share the same right ascension, with the Moon passing 6°15' to the north of Venus. The Moon will be at mag -10.6, and Venus at mag -4.3, both in the constellation Virgo. The pair will be too widely separated to fit within the field of view of a telescope or pair of binoculars but will be visible to the naked eye.

• August 14 – M15 well placed for observation. The globular cluster M15 (NGC 7078) in Pegasus will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of +12°10', it is easiest to see from the northern hemisphere; it can be seen at latitudes between 82°N and 57°S. At magnitude 6.4, M15 is quite faint, and certainly not visible to the naked eye, but can be viewed through a pair of binoculars or a small telescope.

• August 15 – C/2017 S3 (PANSTARRS) reaches its brightest. Comet C/2017 S3 (PANSTARRS) is forecast to reach its brightest, at around mag 2.2. It will lie at a distance of 0.21 AU from the Sun, and at a distance of 0.93 AU from the Earth.

• August 15 – Venus at dichotomy – 05:09 UTC. Venus will be well placed for observation in the evening sky, shining brightly at mag -4.3. Venus's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is very difficult to observe most of the time. It is observable only for a few weeks each time it reaches greatest separation from the Sun – moments referred to as greatest elongation. On these occasions, however, Venus is so bright and conspicuous that it becomes the third brightest object in the sky after the Sun and Moon. It is often called the morning or evening star.

• August 15 – M2 well placed for observation. The globular cluster M2 (NGC 7089) in Aquarius will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -00°49', it is visible across much of the world; it can be seen at latitudes between 69°N and 70°S. At magnitude 6.2, M2 is quite faint, and certainly not visible to the naked eye, but can be viewed through a pair of binoculars or a small telescope.

• August 17 – Venus at greatest eastern elongation. The planet Venus reaches greatest eastern elongation of 45.9 degrees from the Sun. This is the best time to view Venus since it will be at its highest point above the horizon in the evening sky. Look for the bright planet in the western sky after sunset.

• August 17 – Conjunction of the Moon and Jupiter – 10:39 UTC. The Moon and Jupiter will share the same right ascension, with the Moon passing 4°30' to the north of Jupiter. The Moon will be 6 days old. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -11.6, and Jupiter at mag -2.0, both in the constellation Libra. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

• August 17 – Close approach of the Moon and Jupiter – 13:14 UTC. The Moon and Jupiter will make a close approach, passing within 4°17' of each other. The Moon will be 6 days old. The Moon will be at mag -11.7, and Jupiter at mag -2.0, both in the constellation Libra. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars. At around the same time, the two objects will also share the same right ascension – called a conjunction.

• August 19 – 48P/Johnson reaches its brightest. Comet 48P/Johnson is forecast to reach its brightest, at around mag 12.2. It will lie at a distance of 2.01 AU from the Sun, and at a distance of 1.02 AU from the Earth.

• August 21 – Conjunction of the Moon and Saturn – 09:38 UTC. The Moon and Saturn will share the same right ascension, with the Moon passing 2°07' to the north of Saturn. The Moon will be 10 days old. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -12.3, and Saturn at mag 0.1, both in the constellation Sagittarius. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

• August 21 – Close approach of the Moon and Saturn – 09:53 UTC. The Moon and Saturn will make a close approach, passing within 2°07' of each other. The Moon will be 10 days old. The Moon will be at mag -12.3, and Saturn at mag 0.1, both in the constellation Sagittarius. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars. At around the same time, the two objects will also share the same right ascension – called a conjunction.

• August 23 – Conjunction of the Moon and Mars – 17:13 UTC. The Moon and Mars will share the same right ascension, with the Moon passing 6°46' to the north of Mars. The Moon will be 12 days old. The Moon will be at mag -12.4, and Mars at mag -2.3, both in the constellation Capricornus. The pair will be too widely separated to fit within the field of view of a telescope or pair of binoculars but will be visible to the naked eye.

• August 26 – Full Moon – 11:58 UTC. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This full moon was known by early Native American tribes as the Full Sturgeon Moon because the large sturgeon fish of the Great Lakes and other major lakes were more easily caught at this time of year. This moon has also been known as the Green Corn Moon and the Grain Moon. At the exact moment when the Moon reaches full phase, it will lie at a declination of -12°40' in the constellation Aquarius and so will appear highest in the southern hemisphere. It will be visible from all latitudes north of 67°N. Its distance from the Earth will be 402 000 km (250 000 miles).

• August 26 – Mercury at greatest elongation west – 21:48 UTC. The planet Mercury reaches greatest western elongation of 18.3 degrees from the Sun. This is the best time to view Mercury since it will be at its highest point above the horizon in the morning sky. Look for the planet low in the eastern sky just before sunrise.

• August 28 – Mercury at dichotomy – 11:01 UTC. Mercury will be well placed for observation in the dawn sky, shining brightly at mag -0.5. Mercury's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is very difficult to observe most of the time. It is observable only for a few days each time it reaches the greatest separation from the Sun – moments referred to as greatest elongation. Mercury's phase varies depending on its position relative to the Earth. When it passes between the Earth and Sun, for example, the side that is turned towards the Earth is entirely unilluminated, like a new moon. Conversely, when it lies opposite to the Earth in its orbit, passing almost behind the Sun, it appears fully illuminated, like a full moon. However, at this time it is also at its most distant from the Earth, so it is actually fainter than at other times. Mercury shows an intermediate half phase – called dichotomy – at roughly the same moment that it appears furthest from the Sun, at greatest elongation. The exact times of the two events may differ by a few hours, only because Mercury's orbit is not quite perfectly aligned with the ecliptic.

Video courtesy Hubble Space Telescope

Sources: In The Sky by Dominic Ford, NASA, The Watchers

Featured image credit: John Fowler