The Night Sky This Month: August 2021

NGC 4254 as seen with MUSE on ESO’s VLT at several wavelengths
Image credit: ESO/PHANGS

While it has long been known that stars condense out of clouds of dust and gas, much of the details of the mechanisms that initiate the formation of individual stars remain unknown, and even more so when multiple stars form within a confined region in a galaxy.

In efforts to resolve the disparity between where stars actually form in galaxies, and where it is thought they should form, astronomers have developed a method to photograph nearby galaxies, such as NGC 4254, a grand-design spiral, in frequencies that span the entire electromagnetic spectrum. This method revealed the actual locations of star-forming regions within galaxies, which somewhat surprisingly differed significantly from where astronomers had thought they should (or would) be.

This method of looking at galaxies is able to resolve individual star-forming regions in this galaxy, shown here as glowing, golden splotches of light, but it can as yet not resolve the actual processes that drive star formation in each glowing area. Nonetheless, by comparing the areas of current star formation with the bluish regions, which are concentrations of older stars, astronomers are now better able to analyze the flows of dust, gas, and ionized material that eventually condense into individual stars.

The Moon Phases in August 2021

Last Quarter New Moon
First Quarter
Full Moon
July 31st August 8th August 15th August 22nd

Note that the Full Moon occurring on the 22nd of the month will be the third of four Full Moons of this season, which means that this Full Moon counts as a “Blue Moon”.

The Planets in August 2021

Planetary viewing remains poor, with several planets being inaccessible for observers north of London (UK), which is at latitude 51.51N. Below are some details of what you can expect to see, or not see, as the case may be – all times are given in BST (British Standard Time).

Mercury starts the month only one degree away from the Sun, and as a result, it will remain inaccessible to most northern hemisphere observers, since it will reach its highest elevation above the horizon during daylight hours.

Venus starts the month at superior solar conjunction, and it will therefore reach its highest elevation during daylight hours. However, by month’s end, the planet will become visible as an early evening object that will be higher about 5 degrees above the horizon at dusk.

Mars is now approaching a point of conjunction with the Sun, and it will therefore not be visible throughout the month of August.

Jupiter is now visible as an early morning object since it is approaching a point of opposition. As seen from London, the ‘King of the Planets’ becomes visible from about 22:35 (BST) at an elevation of about 8 degrees above the southeastern horizon, rising to about 25 degrees above the horizon by around 02:31 (BST). By month’s end, Jupiter will become inaccessible at about 04:05 (BST) when it sinks below 8 degrees above the southwestern horizon.

Saturn, is like Jupiter, approaching a point of opposition, and is therefore visible as an early morning object from about 22:20 (BST) and 04:08 (BST). Note, however, that by month’s end, Saturn will have passed opposition, and will therefore become visible as an early evening object from 20:30 (BST), at an elevation of 11 degrees above the southeastern horizon. Sadly though, the planet will not rise above 19 degrees at any point during the month, which could make it somewhat difficult to obtain clear views of.

– Uranus is now visible as a pre-dawn object, rising to about 34 degrees above the eastern horizon. Look for the gas giant from about 23:41 (BST), but note that will become lost to the brightening dawn sky from about 03:37 (BST) by the end of the month.

– Neptune is also visible as an early morning object, rising as it does in the south at about 22:14 (BST). From London, the gas planet will rise to about 34 degrees above the horizon at the start of the month, which will reduce to only about 21 degrees by the end of the month.

Meteor Showers in August 2021

The Perseids Meteor Shower is generally regarded as one of the most productive showers because it can deliver upwards of 60 meteors per hour at its peak, which is expected to occur in the pre-dawn hours on the 13th of August.

Created by debris left behind by the comet Swift-Tuttle, the Perseids is known to produce a relatively large number of bright, fast-moving meteors, which should be even more spectacular this year because there will be no moonlight during the peak. While the shower’s radiant is in the constellation Perseus, meteors can appear from anywhere in the sky.

Deep Sky Objects to Look for in August 2021

Provided seeing conditions allow at this time of the year, the northern sky contains many spectacular deep sky objects that are easy targets for modest amateur equipment such as large binoculars and small telescopes. Below are some details of few such objects, although you may have some trouble finding the diminutive constellation Sagitta, which contains several deep sky objects, including one Messier object, that are worth hunting down.

Messier 56 (M56, NGC 6779)

Messier 56
Image credit: NASA

Located about 33,000 light years away in the constellation Lyra, this 84 light-year wide cluster is thought to have formed when the Milky Way assimilated a small, dwarf galaxy, of which the massive globular cluster Omega Centauri is the surviving nucleus.

Despite its mass of about 230,000 Suns, the star cluster is moving through space at a rate of at least 177 km/second. Investigators believe that the cluster’s high rate of movement through the galactic halo is heating the interstellar medium to temperatures of at least 940,000 K, thus creating the observed high-intensity X-ray emissions in the cluster’s wake.

Look for this 13.7-billion-year-old cluster at about the midpoint between the stars Albireo (Beta Cygni) and Sulafat (Gamma Lyrae). Nevertheless, a small telescope is required to get the best views of this ancient cluster.

Messier 71 (M71, NGC 6838)

Messier 71
Image credit: Calar Alto Observatory / T. Credner and S. Kohle

Located about 12,000 light years away in the small constellation Sagitta, this loosely packed globular cluster was for many years believed to be an extraordinarily dense open cluster because, unlike other globular clusters, this cluster lacked a dense core.

However, the cluster holds some scientific interest since it also lacks the RR Lyrae variable stars that are a common, if not an always expected feature of the Milky Way’s globular clusters. On average, the cluster’s stars are between 9 and 10 billion years old, and all told, they span across about 27 light years, giving the cluster a mass of about 53,000 Suns, and a luminosity of about 19,000 times that of the Sun.

The Glowing Eye Nebula – NGC 6751

The Glowing Eye Nebula
Image credit: NASA

Located about 6,500 light years away in the constellation Aquila, this magnitude 11.9 planetary nebula spans across a distance of about 0.8 light years, which in practical terms, is about 600 times bigger than the solar system. The bright spot in the centre of the nebula is the remains of the progenitor star, which currently has a surface temperature of around 140,000 degrees Celsius. The nebula is expanding at the rate of 40 km every second.

Look for this pretty nebula, an image of which was chosen to commemorate the 10th anniversary of the Hubble Space Telescope, about 1.1 degrees to the southward of the star Lambda Aquilae.

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