The Night Sky This Month: July 2021

Night Sky 4
Image Credit: Adam Mescher

While free-floating clouds of gas are not exactly rare in the Universe, this particular cloud seen in above image has been puzzling astronomers since 2017, when it was first discovered by the Japanese Subaru telescope. Located among several members of the Abell 1367 cluster of galaxies about 300 million light years away, this cloud of gas is significantly bigger than the Milky Way galaxy and radiates in both optical and X-ray light frequencies.

The origin of this huge cloud of gas is still uncertain, although many investigators are surmising that it must somehow have become separated or dislodged from one or more of the galaxies in the cluster during a close encounter between two or more members of the group. However it was formed, though, most investigators also seem to agree that it must be held together by an intense magnetic field that prevents it from being dispersed by the gravitational influences of nearby galaxies.

In this rendition, X-ray emissions are shown in blue, while warmer gas is rendered in red. The white parts in this view show diffused light from individual members of the group of galaxies.

The Moon Phases in July 2021

New Moon First Quarter Full Moon Last Quarter
July 10th July 17th July 24th July 31st

The Planets in July 2021

Planetary viewing is exceedingly poor this month, with almost all the inner planets not being visible from as far south as London (51.5°N). Nonetheless, some details of which planets are observable and which are not, are listed below-

Mercury is now well past its point of greatest western elongation from the Sun, and as a result, it is just visible less than 5 degrees above the horizon at dawn. Since the little planet reaches its highest elevation during the daylight hours, it will generally not be visible throughout July.

Venus was recently at superior conjunction with the Sun, and although it is now visible as an early evening object, it will not rise about 7 degrees above the horizon just before sunset. Moreover, it will reach its highest elevation during daylight hours, and will therefore not be observable from south of London.

Mars is now approaching a point of superior conjunction with the Sun and will remain at, or below 1 degree above the horizon just before sunset.

Jupiter is now approaching a point of opposition and is therefore visible as an early morning object from the southern reaches of the UK. However, note that while the ‘King of the Planets’ becomes visible from about 23:43 (BST), it will only rise to about 26 or so degrees above the southern horizon, which might make it difficult to obtain clear views of the planet.

Saturn follows Jupiter, and like Jupiter, it is also approaching appoint of opposition. As a result, Saturn will become visible as an early morning object from about 23:27 (BST) at an elevation of about 10 degrees above the southeastern horizon. By about 04:10 (BST) it will be about 16 degrees above the southwestern horizon, so it might be difficult to obtain clear views of the planet.

– Uranus is just emerging from behind the Sun and will be visible to observers south of London as an early morning object, but note that it will not rise above about 18 degrees above the horizon.

– Neptune becomes visible as an early morning object from about 23:19 (BST), and unlike the other planets, it will rise to an elevation of about 28 degrees above the southeastern horizon at dawn as seen from London.

Meteor Showers in July 2021

July sees the arrival of the Delta Aquarids Meteor Shower, which is expected to peak after midnight between the 28th and 29th of July. This shower is created by debris from the comets Marsden and Kracht, and although it can produce up to about 20 meteors per hour during the peak, the still-nearly Full Moon will extinguish all but the brightest meteors this year.

The best places to view the Delta Aquarids Meteor Shower this year would be under dark skies, well away from all sources of light pollution.

Deep Sky Objects to Look for in July 2021

Some of the most prominent constellations at this time of the year include Perseus, Hercules, and Ursa Major, all of which contain a large number of spectacular deep sky objects that are easy targets for modest amateur equipment. Below are some details of such objects, two of which are naked-eye objects under dark skies-

Perseus Double Cluster (C 14, NGC 869, Cr 24, Mel 13)

Perseus Double Cluster
Image credit: Second Digitized Sky Survey (DSS2)

Located about 7,500 light years away in the constellation Perseus, this complex open cluster consists of two separate open clusters, designated NGC 869 and NGC 884. Both clusters are visible without optical aid, but even a pair of binoculars will resolve individual stars in the complex.

Unlike most other open clusters, which are relatively light, NGC 869 weighs in at about 3,700 solar masses, while NGC 884 boasts about 2,800 solar masses. However, intensive studies have shown that both clusters are surrounded by a common halo of stars, which raises the mass of the entire complex of stars to at least 20,000 solar masses.

Both clusters also contain at least 300 blue-white super-giant stars, and both clusters are blue-shifted; NGC 869 is approaching Earth at a velocity of 39 km/s, while NGC 884 is approaching Earth at a velocity of 38 km/s.

The entire complex of stars is close to being circumpolar, and as a result, it is visible for most of the night, but it will reach its highest elevation at about 02:58 (BST) when it will be about 49 degrees above the northeastern horizon.

The Great Hercules Globular Cluster (M13, NGC 6205, Mel 150)

Great Hercules Globular Cluster
Image credit: Second Digitized Sky Survey (DSS2)

Located between 22,000 and 25,000 light years away in the great constellation Hercules, this globular cluster is among the biggest and brightest globular clusters visible from the Northern Hemisphere. All told, it contains several hundred thousand stars that span across a distance of about 145 light years.

However, the stars in the cluster are packed so closely together that stars often collide or merge, which explains the high number of so-called “blue-straggler” stars, which are stars that have merged, and are, therefore, hotter, bigger, heavier, and more active than their age would suggest. In general, most, if not all of the stars in M13 are at least one hundred times closer to each other than the stars in the Sun’s immediate vicinity are.

 Bode’s Nebula (Bode’s Galaxy, M81, NGC 3031)

Bode's Nebula
Image credit: Second Digitized Sky Survey (DSS2)

Located about 12 million light years away in the constellation Ursa Major, this grand design spiral galaxy is only about 90,000 light years in diameter. Nonetheless, while it is considerably smaller than the Milky Way it contains a supermassive black hole in its core, which is estimated to weigh in at about 70 million solar masses.

Moreover, despite its modest size, the galaxy contains between 180 and 240 massive globular clusters, which compares favorably with the number of globular clusters the much larger Milky Way galaxy hosts.

Look for this grand spiral galaxy about 10 degrees to the northwestward of the bright star Alpha Ursae Majoris (Dubhe), but note that you need at least an 8-inch telescope to resolve structure in the galaxy.

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