July: Milky Way star fields a joy to explore

The Lambda Centauri nebula, a star-forming cloud in our Milky Way galaxy, is also known as the Running Chicken nebula. The nebula, catalogued as IC 2944, is about 5800 light-years from Earth and is home to a new cluster of stars born from the cloud nearly eight million years ago. It gets its name because it appears to surround the bright star Lambda Centauri, which is one of the brightest stars in the constellation Centaurus. Photo: MPAS member Nick Axaris

Scorpius is easy to spot sitting high in the sky this month, being one of the brightest constellations in the sky. Nearby are the constellations Sagittarius and the slightly less prominent Libra. When you look towards Sagittarius and Scorpius, you are peering towards the centre of the Milky Way galaxy.

This whole region is full of rich and beautiful star fields, which are a joy to explore using binoculars. If you look at the constellation Libra, the Scales, look out for the second brightest star, which is called Zubenelgenubi (Arabic for ‘the Southern Claw’) and is the brighter component of the Alpha Librae system. This is a binary star system with the two stars in orbit around each other, and a pair of binoculars easily shows its two stars.

A little lower in the sky are the bright stars Alpha and Beta Centauri, also known as Rigil Kentaurus and Hadar respectively, or simply ‘The Pointers’, as they appear to be pointing to the smallest constellation in the night sky – Crux, or the Southern Cross.

On July 4, the Earth is at aphelion, which is when it is at its farthest point from the sun. It is about 4,800,000km farther from the sun than when at its perihelion in early January.

When two astronomical objects appear close to each other in the sky it is called a conjunction, and there are a few in July. On July 16 is the conjunction of the moon and Saturn, July 19 the moon and Jupiter, and July 22 the moon and Mars.

Then Jupiter enters retrograde motion on July 29, which is an apparent change in the movement of the planet through the sky. It is not real, in that the planet does not physically start moving backwards in its orbit. It just appears to do so because of the relative positions of the planet and Earth and how they are moving around the sun. Jupiter will appear in retrograde motion for 119 days, then become progressive again in November.

By Nerida Langcake
This article appeared in the July 2022 issue of the Mornington Peninsula Magazine.