The Night Sky This Month: August 2019

August 2019 Night Sky
Image Credit: NASA

The Summer Triangle, whose outline is marked by the brightest stars in the constellations of Cygnus, Aquila, and Lyra, appears almost directly overhead at midnight in the August night sky. Meanwhile, the stunning constellation of Scorpius moves on its belly close to the southern horizon, while in the northern sky the ever present circumpolar constellations are visible, including Ursa Major, Ursa Minor, Cassiopeia, Cepheus, and Draco.

Stargazers can also look forward to seeing Jupiter due south at nightfall. Of course, the Perseid meteor shower, one of the top 10 meteor showers of the year, will also be reaching its peak on the 12th/13th of the month.

The Moon in August 2019

Favourable illumination on the 8th and again on the 21st will offer lunar observers two excellent opportunities to view the Hyginus Crater and Rille. This crater is arguably the only crater on the Moon’s surface that was not caused by an impact; it is thought by most planetary scientists to have been caused by an underground explosion in the rille that cuts through the crater. Although the exact mechanism of its formation is not clear, the rille that cuts through the crater is a collapsed lava tube which is similar, if not identical, to the extant lava tubes that can be seen in Hawaii.

Moon Phases In August 2019

New Moon First Quarter Full Moon Third Quarter
August 1st August 7th August 15th August 23rd

Note that in the predawn hours on the 24th August the Moon will occult the bright stars Delta 1 Taurii and Delta 2 Taurii in the Hyades cluster in the constellation Taurus. Ingress for Delta 1 Tarii starts at 03:43 BST, and egress for Delta 2 Taurii occurs at 05:16 BST.

The Planets In August 2019

August 2019 is not a good time to view the planets, but for those observers that are willing to attempt views of the visible planets, here is what to expect:

Mercury is now west of the Sun following its recent inferior conjunction, and starts the month shining at magnitude +1.2 for about 40 minutes before dawn about 5 degrees above the east-north-eastern horizon. However, by the middle of the month, the little planet will have risen to about 8 degrees above the horizon. Note that while a small telescope will show the planet as a disc with an angular diameter of about 7 seconds of arc with a phase of about 52% from the 10-16th of August, the planet will rapidly become lost in the glare of the Sun during the last week of August.

Venus is now approaching a point of superior conjunction with the Sun, and will therefore not be visible for the next several months.

Mars, like Venus, will also pass behind the Sun, and will likewise not be visible for the next several months.

Jupiter starts the month shining at magnitude -2.41 almost due south after sunset. By the 11th August the planet will cease its retrograde motion, and will begin to recede from its current position about seven degrees from the bright star Antares in the constellation Scorpius. However, while the King of the planets is relatively bright, it will not rise more than about 14 degrees above the southern horizon as seen from central Britain, which means it might be difficult to get clear views of the planet through the murkiness of the atmosphere.  The use of an atmospheric dispersion corrector is therefore recommended to obtain reasonable, if not clear views of the planet.

Saturn, like Jupiter, will not rise more than about 14 degrees above the southern horizon when it transits the meridian. Nonetheless, the planet starts the month shining at magnitude +0.16, which reduces to magnitude +0.33, while its angular diameter shrinks to only 17.6 seconds of arc. Happily, though, the planet’s ring system still spans across 42.5 seconds of arc, meaning that reasonable views of the planet could be had with a good telescope and the aid of an atmospheric dispersion corrector.

Meteor Showers in August 2019

The Perseid meteor shower is expected to peak in the predawn hours of the 12th/13th of August. This shower is produced by the debris of the comet Swift-Tuttle, and although the peak is relatively broad and increased meteor activity can be seen for two or three days on either side of the peak date, bright moonlight this year will spoil visibility of all but the brightest meteors. Note though that actual radiant of the shower is located between the constellations Perseus and Cassiopeia.

Deep Sky Objects to Look For In August 2019

Apart from the north circumpolar constellations, other prominent constellations include Hercules, Sagittarius, Scorpius, Corona Borealis, Bootes and Aquila, the Eagle, now rising in the east. All of these constellations contain a large variety of easy targets for binoculars and small telescopes, a few of which are briefly described below-

The Great Globular Cluster – Messier 13 (M13, NGC 6205)

Great Globular Cluster
Image Credit: NASA

Also known as the Great Hercules Cluster, M13 is the brightest globular cluster in the northern sky, with an apparent magnitude of 5.8. All told, the cluster contains about 300,000 stars that are packed into a sphere that spans only about 145 light years, meaning that the average stellar density of the cluster is at least 100 times greater than the stellar density in the Sun’s immediate vicinity.

In fact, the stars in the cluster are so closely packed that collisions between stars occur relatively frequently, which explains the high number of “blue stragglers” in the cluster. These stars are so-called because the merger of two stars creates a “new” star that is bigger, more massive, and hotter than the two progenitor stars were at the time of the merger.

Messier 92 (M92, NGC 6341)

Messier 92
Image Credit: NASA

Also located in Hercules, M92 is not only among the brightest of the northern globular clusters, it is also among the oldest of all the globular clusters that are associated with the Milky Way galaxy. What is most remarkable about this cluster is the fact that despite its age of about 14 billion years, it has not undergone a process of core collapse, which is a sort of gravitational “sifting” of the more massive stars in the cluster towards the cluster’s core.

One possible explanation for this is that because all the stars in the cluster are very old Population II stars, they are all equally metal-poor, which accounts for the lack of differential stellar masses in the cluster.

NGC 6760

NGC 6760
Image Credit: NASA and ESA

Located in the constellation Aquila, NGC 6760 is a small but striking globular cluster. NGC 6760 also forms a dramatic colour contrast with NGC 6749, with the arc of young, hot blue stars they seem to bracket. Located only 1.72 minutes of arc apart, both clusters can be seen in a single field of view.

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