The Night Sky in September
September hosts the second equinox of the year, when the Sun moves from the northern to the southern half of the sky. It also represents, for the Northern Hemisphere at least, the period when the rate of increase in the length of night is at its greatest. Neptune comes to opposition, when a planet appears in the opposite part of the sky to the Sun, on Sept 10.
For planets closer to Earth such as Mars, Jupiter and Saturn, opposition makes a big difference to their appearance. For the outer planets Uranus and Neptune, opposition doesn’t really make much of an adjustment to our view, although it does mean that they are visible all night long.
The big, bright and detailed gas giants of Jupiter and Saturn appear low from the UK. As darkness falls you can see Saturn low above the southern horizon with brighter
Jupiter low in the south-southwest. The so-called Ice Giants, Uranus and Neptune follow on later in the night with a better height relative to the horizon. This gives us an improved opportunity to study them above the murky, turbulent atmosphere which occurs low down.
Neptune is easy to locate as it is well placed close to the dim star Phi Aquarii. Neptune is the only planet that requires optical assistance to see, its brightness being below naked-eye threshold of even the darkest skies.
Uranus hovers just above this but it’s a far from easy spot. Through binoculars, both worlds look like stars. It’s not until you engage the extra-light grasp and magnification of a telescope that the planetary nature becomes evident. Both show tiny discs but it’s their colours that make them stand out.
Neptune appears with a blue hue while Uranus looks like a tiny emerald. Early during a September evening, the W-shaped constellation of Cassiopeia the Seated Queen can be seen climbing high in the northeast. A binocular sweep reveals many impressive star clusters. A particularly interesting example lies just south of the star Ruchbah (Delta Cassiopeiae). Here you’ll find the dim star Phi Cassiopeiae, which has an even dimmer neighbour known as HIP 6229 (HIP indicates that this is the star’s Hipparcos Catalogue reference).
Together these stars represent the eyes of an owl, the body of which is formed by the adjacent cluster NGC 457, the Owl Cluster. It’s also known as the ET Cluster, the star layout invoking the memory of the squat alien in ET: the Extra-terrestrial.
Extend the line from the Cassiopeia’s central star through Ruchbah for approximately twice that distance again and you’ll arrive at the wonderful sight of the Double Cluster, Chi and H Persei.
This resides in the constellation of Perseus the Greek Hero. It is also known as the Perseus Sword Handle. Both clusters are just visible with the naked eye on a dark night, but it takes binoculars to see their full glory: a stunning sight which resembles two piles of salt poured on black velvet.
The W of Cassiopeia can be used to locate another interesting object known as Kemble’s Cascade. This resides in the frankly obscure constellation of Camelopardalis the Giraffe. It was named after the Franciscan friar, Father Lucian Kemble. A keen astronomer, Kemble wrote about the pattern to Walter Houston, who named it Kemble’s Cascade in a magazine in 1980. Through binoculars or telescope it really is quite impressive, resembling a waterfall of stars ending in a splashpool.