The Night Sky This Month: July 2018

Blood Moon
Image Credit: NASA

In the northern hemisphere, July presents an ideal opportunity to stargaze whilst enjoying pleasant outdoor conditions, so don’t forget to make the most of the warm nights by familiarizing yourself with some of the spectacular astronomical objects the summer sky has to offer.

Look out for the asterism recently dubbed the ‘Jupiter Triangle’, which can be seen in July’s early evening sky, and showcases Arcturus, the red giant star in Bootes, and the blue-white star Spica in Virgo, as well as the King of Planets, Jupiter. As this beautiful formation moves westwards, the evening sky is then dominated by another magnificent asterism called the Summer Triangle, comprising the three brightest stars in the constellation Lyra, Aquila, and Cygnus, with the Milky Way passing between the stars Vega and Altair, and running through Deneb.

Moon

The image above shows a blood Moon, and with some luck and weather permitting, most observers in the UK will see a similar sight during the total lunar eclipse that will be visible from the entire country on July 27th. Sadly, though, the eclipse will already have started when the Moon rises over London at about 8.50 PM (Local Time) but to compensate, the entire event will last for more than 100 minutes, making this the longest-lasting lunar eclipse of the 21st century.

Phases

Last Quarter: 6th
New Moon: 13th
First Quarter: 19th
Full Moon: 27th

Planets

Mercury will shine at about zeroth magnitude (magnitude 0.0, about as bright as the star Vega), at the start of the month, but will have dimmed slightly to magnitude +1 when it reaches its point of greatest western elongation from the Sun on the 12th. By the 17th of July, Mercury will be visible toward the lower right of the planet Venus, but it will be lost in the Sun’s glare from that date onwards.

Venus still dominates the early evening sky in the west, but it will continue to sink towards the horizon as the month wears on. However, while its illumination decreases from about 70% to less than 57%, its angular diameter will increase from 16 seconds of arc to just over 20 seconds of arc, meaning that its brightness will remain fairly constant at about magnitude -4.2 throughout the month. Look for Venus close to the bright star Regulus in Leo on the 9th, and close to the waxing crescent Moon on the 15th.

Mars is still in the constellation Capricornus, but has been moving westwards towards a point of closest approach to Earth since 2003, which position it will reach on the night of July 30th/31st . Mars starts the month rising about 2 hours or so after sunset and its brightness will increase from about magnitude -2.2 to about magnitude -2.8 during the last days of July, while its angular diameter will increase to more than 24 seconds of arc by the first week of August. However, the red planet will achieve its highest elevation at only about 14 degrees above the horizon for observers in the UK, which will make it difficult to spot large surface details on the planet.

Saturn was in opposition during the last week of June, and the planet will therefore remain visible throughout the night for most observers in the northern hemisphere. Rising in the constellation Sagittarius, close to the topmost star of the “Teapot” asterism, Saturn will not rise much higher than about 15 degrees when it culminates in the south, meaning that it will be difficult to get clear views of the ring system without the aid of an atmospheric dispersion corrector.

Jupiter rises almost due south soon after sunset at the start of July, but rises progressively more towards the southwest as the month wears on. Starting the month at magnitude -2.3, the King of the planets will dim slightly to magnitude -2.1 as its angular diameter decreases to 38 seconds of arc from 41.5 seconds of arc. Note that Jupiter is now moving towards the southern part of the ecliptic, and will therefore not rise more than 20 degrees above the horizon when it transits the meridian. Getting clear views of the planet will therefore be difficult without the aid of an atmospheric dispersion corrector.

Meteor Showers

July sees the Delta Aquariids, a minor shower that runs from the middle of July to about the middle of August, with the peak expected to fall on the night of 29th/29th July. Although the shower is best seen from the southern hemisphere, observers that are away from big cities might see a few meteors per hour, but since the Moon will be full on the night of the expected peak, the shower is not expected to deliver spectacular viewing.

Deep-Sky Objects

Two constellations, Hercules and Cygnus, offer some spectacular targets for viewing with binoculars and small telescopes at this time of the year. Below are some details:

Messier 13M13 (M13) is the brightest, and most beautiful globular cluster that is visible from the northern hemisphere, and under dark skies, it is faintly visible with the naked eye. With a mall telescope or even binoculars, the cluster looks like a ball of cotton wool about 30% as big as the full Moon. All told, the cluster contains about 300 000 stars packed into s pace that measures only 100 light years across, with the highest concentration of stars concentrated in the inner few tens of light years.

Brocchi’s Cluster, resembling an upside down “Coathanger” in the constellation Cygnus, is perhaps the best-known asterism in the entire northern sky, and well worth the time to find. Follow the neck of the Swan down towards the double star Albireo, and continue to sweep downwards towards its lower left. You might miss it at first, but once you find it, the collection of bright stars will appear to jump out at you from the dark lane of dust behind them.

North America NebulaNorth America Nebula in the constellation Cygnus, located slightly above and to the left of the star Deneb, is a huge area of nebulosity that with some imagination, looks like the North American continent, hence the name, North America Nebula. Another famous nebula, the Pelican Nebula, is located just to the right of the main area of nebulosity, and again with some imagination, the head, beak, and eye of a pelican becomes visible. Note though that the darker the sky, the better the chance becomes to see the celestial sea bird.

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