The Night Sky in July 2018

Lyra – Lyra’s brightest star Vega, fifth brightest star in the sky. A blue-white star, 25.3 light years away. Its’ mass is 3 times that of the Sun and is about 50 times brighter. It burns its nuclear fuel at a greater rate than the Sun and therefore will shine for a correspondingly shorter time. Vega is younger than the Sun, only a few hundred million years old, and is surrounded by a cold, dark disc of dust in which an embryonic solar system is being formed!

There is a double star called Epsilon Lyrae up and to the left of Vega. A pair of binoculars will show them up easily – it may be possible to see them without optical aid.

Using a telescope, provided good viewing, shows each of the two stars seen is a double star also so it is called the double double!

Fig 1


Cygnus, the Swan, sometimes called the "Northern Cross" because of a distinctive cross shape, but we normally think of it as a flying Swan. Deneb, the Arabic word for "tail", marks the tail of the swan. It is approximately 2600 light years away and appears so bright because it gives out around 80,000 times as much light as the Sun. If Deneb where as close as the brightest star in the northern sky, Sirius, it would appear as brilliant as the half moon and the sky would never be really dark when it was above the horizon!

The star, Albireo, head of the Swan is fainter, but a good sight in a small telescope. Albireo is made of two stars, amber and blue-green, which provide a wonderful colour contrast. They are regarded as the most beautiful double star that can be seen.

Cygnus lies along the line of the Milky Way, the disk of our own Galaxy, and provides a wealth of stars and clusters to observe. Just to the left of the line joining Deneb and Sadr, the star at the centre of the outstretched wings, you may, under clear dark skies, see a region which is darker than the surroundings. This is the Cygnus Rift and caused by the obscuration of light from distant stars by a lane of dust in our local spiral arm. The dust comes from elements such as carbon which have been built up in stars and ejected into space through explosions that give rise to objects such as the planetary nebula M57 (Fig 1).

The constellation Ursa Major

The map (Fig 2) shows constellations seen towards the south at about 10pm BST in mid, July. A prominent star, slightly west of South, is Arcturus in Bootes. The second (after Sirius) brightest star in the northern sky.  High overhead towards the north (not on the chart) and up to the right of Arcturus lies Ursa Major with its prominent grouping of the Plough. Moving southwards to the left of Bootes you cross the constellation Hercules with its globular cluster, M13, and then across the large but not prominent constellation Ophiucus until, low above the southern horizon lie Sagittarius and Scorpius. South of the UK - and better in Southern Europe is bright red star Antares.  Rising in the east is the region of the Milky Way containing both Cygnus and Lyra.  Below is Aquilla. Three bright stars Deneb (in Cygnus), Vega (in Lyra) and Altair (in Aquila) make up the "Summer Triangle."

Fig 2

Fig 3

Stars of the Plough, shown linked by the thicker lines (Fig 3), form one of the most recognised star patterns in the sky. Also called the Big Dipper, it forms part of the Great Bear constellation – not easy to make out! The stars Merak and Dubhe form the pointers which lead to the Pole Star, and finding North. Stars Alcor and Mizar form a naked eye double which repays observation in a small telescope as Mizar is then shown to be an easily resolved double star. A fainter reddish star forms a triangle with Alcor and Mizar.

Ursa Major contains interesting "deep sky" objects. The brightest, listed in Messier's Catalogue, are shown on the chart, but there are many fainter galaxies in the region also. Upper right of the constellation are a pair of interacting galaxies M81 and M82 (Fig 4). M82 is undergoing major bursts of star formation and is called a "starburst galaxy". They can be seen using low power eyepiece on small telescopes.

Fig 4 (M81 and M82)

Fig 5

Between constellations Bootes and bright star Vega in Lyra lies the constellation Hercules (Fig 5). Red Giant star Alpha Herculis or Ras Algethi, its Arabic name, is one of the largest stars known, diameter approximately 500 times that of the Sun. The brightness increases towards the centre where concentration of stars is greatest. Beautiful sight through small telescopes. It contains approximately 300,000 stars in a region of space 100 light years across, and is the brightest globular cluster that can be seen in the northern hemisphere.


Mercury shining around zeroth magnitude early month reaching greatest elongation west of the Sun July 12th.   It will then be seen about 15 degrees down to the lower right of Venus but will have dimmed by the 17th and then rapidly fade from view into the Sun's glare.

July 9th - sunset: Venus close to Regulus in Leo. 45 minutes after sunset on 9th, you may see Venus shining brightly up to the right of Regulus in Leo.

July 10th before dawn: The Moon in Hyades Cluster. A thin waning crescent Moon will be seen amongst the Hyades Cluster.

July 15th, after sunset: Venus to the left of a very thin crescent Moon. After sunset and given a very low western horizon.

July 19th after sunset: If clear, Jupiter below a waxing Moon. Alpha Libri is to its lower left.

July 24th after sunset: Saturn close to a waxing Moon. To the lower left of the waxing Moon.

Mark R Smith FRAS
Nuclear Fusion & Astrophysics