Stargazing: This month’s night sky

July 2020

Gas giant planets Jupiter and Saturn keep us company through summer nights, rising together as the sky darkens and disappearing below the south western horizon around dawn.

Stars to look out for:

The summer sky is dominated by a bright triangle of stars in the south that’s hard to miss once you know what you’re looking for. Known as the ‘summer triangle’ this asterism (star pattern) is made up of the brightest stars in three summer constellations: Vega in the constellation Lyra the Harp, Altair in Aquila the Eagle and Deneb the tail star of Cygnus the Swan.

The triangle covers a large area of sky as you look to the south, and ‘points’ to the southern horizon. Once you find the triangle itself, it’s much easier to spot the shape of the constellations within it. See below…

Note: ‘asterisms’ are not official constellations. They are groups of stars that form an easy to recognize shape and may be made up of stars from the same or different constellations.

Well known asterisms include: the Plough (in the Great Bear), the Keystone (in Hercules) and the Square of Pegasus (in Pegasus the flying horse).

Deneb (‘tail’ in Arabic) forms the top left of the summer triangle. Cygnus is sometimes called the ‘northern cross’. Vega is the top right of the triangle – look for the ‘squashed box’ of Lyra the Harp. Altair (meaning ‘flying’ in Arabic) is the third point of the triangle and the middle of three stars in a line marking the head of Aquila the Eagle.

The summer triangle straddles something that’s a lot harder to spot – a hazy band of light forming an arch overhead, which could easily be mistaken for wisps of cloud. This is the faint light of our galaxy, the Milky Way (left, Wikicommons)

Galaxies are ‘star cities’, being made up of millions of stars, gas and dust, all held together by the force of gravity. They come in different shapes and sizes, although many are disc-shaped or spirals. The Milky Way is a spiral galaxy, shaped much like this one (right, ESO).

So if it’s a spiral, why does the Milky Way appear as a ribbon of light across the sky?

The Earth and entire solar system is located in one of the spiral arms of our galaxy. This means that we can never get an ‘outside view’ of the Milky Way like the image above. Instead we have to interpret its shape from the inside, by gathering data with telescopes and making comparisons with the range of galaxies that we see beyond our own.

The sun is just one of the 100,000 million or so stars that form our galaxy – all the stars we can see in our sky are part of our galaxy too. The band that we refer to as ‘the Milky Way’ is brighter than the rest of the sky because more stars lie in that direction; a result of seeing the spiral shape sideways on.

The gas and dust in the galaxy scatter the light of the many stars, rather like fog scatters the light from a torch, making it appear hazy. The name of our galaxy comes from its pale appearance, looking to the ancient Greeks as if milk had been spilt across the sky.

Planets:

Jupiter and Saturn shine brightly through the night, becoming visible low in the SE as dusk falls. Jupiter is currently the more westerly and rises first, also appearing much brighter of the two.

Mars rises in the east around midnight and brightens as the month progresses.

Mercury appears in the early morning sky towards the end of the month. Sharp-eyed observers may find it to the left of Venus close to the eastern horizon.

Venus shines brilliantly in predawn skies. It rises in the east around 2.30am, ahead of the Sun.

Moon phases:

Full Moon 5 July
Third Quarter 13 July
New Moon 20 July
First Quater 27 July

Spacecraft:

To find out times to view the ISS from your location check out this page

Look out for news about spacecraft heading for Mars- Launches planned for July 2020 include NASA’s Mars 2020 spacecraft with Perseverance Rover, China’s Tianwen-1 (meaning ‘Heavenly Questions’) which will carry an orbiter, lander and rover and the UAE’s ‘Hope’ mission which will focus on studies of the Martian atmosphere. Find out more here:

 Happy Stargazing!