BBC Sky at Night Magazine
Best time to see: 30 September, 02:00 BST (01:00 UT)
Features: Dark ‘albedo’ features, polar caps, weather
150mm or larger
Mars now dominates the night sky, its gorgeous salmon-pink colour glowing like an ember within the constellation of Pisces. Fast approaching a favourable opposition in the middle of next month, Mars can be seen doing several remarkable things during September.
On 10 September the planet’s apparent eastward motion against the background stars stops as Mars reaches what’s known as a stationary point. After this Mars will appear to move west until it reaches its next stationary point in mid-November. In reality, Mars hasn’t changed direction at all, the effect is simply a consequence of Earth’s own orbital motion relative to that of Mars.
The size of Mars increases dramatically this month too. On 1 September a telescope shows the planet to have an apparent size of 18 arcseconds. By the time 30 September has come around, Mars will have grown to appear 22 arcseconds across; a 22% increase in size. The planet’s increase in brightness is just as dramatic, Mars brightening from mag. –1.8 on 1 September to mag. –2.5 by the month’s end. Midmonth, Mars overtakes Jupiter in the brightness stakes to become the second brightest planet in the sky after Venus.
On the evening of 5 September Mars is joined by an 87%-lit waning gibbous Moon.
At 23:00 BST (22:00 UT) on 5 September both objects appear 3.2˚ apart, measured from the centre of the Moon’s disc. Over the remainder of the night and into the morning of 6 September, the separation continues to get smaller. It reaches a minimum value of half a degree around 06:30 BST (05:30 UT) under daylight conditions. With Mars being so bright at this time, it should be easy to follow the pair with binoculars or a telescope despite the Sun being up.
Best time to see:
14 September, from
04:00 BST (03:00 UT) Altitude: 10˚
Venus is a morning planet and well positioned all month, rising four hours before the Sun.
Its phase and size changes dramatically when viewed through a scope in September. On the 1st, shining at mag. –4.1, Venus presents a 19 arcsecond disc, 59%-lit. By the month’s end, having dimmed to mag. –4.0, Venus presents a 15 arcsecond disc, 71%-lit.
The 14th is the best time to see the planet visually, as this is when Venus and a slender crescent Moon sit either side of the Beehive Cluster.
Best time to see: 1 September, 21:30 BST (20:30 UT) Altitude: 14˚
Location: Sagittarius Direction: South
Jupiter is an evening object, reaching its highest position as darkness begins to set in at the month’s start. It remains low and is joined by Saturn to the east. On the 1st Jupiter shines at mag. –2.4, dropping to mag. –2.2 by the month’s end. A gibbous Moon sits near to Jupiter and Saturn on the evenings of the 24th and 25th.
Best time to see: 1 August, 00:30 BST (23:30 UT) Altitude: 16˚
Location: Sagittarius Direction: South
Saturn appears east of Jupiter, the pair being 7.4˚ apart on the 30th. It appears low from the UK, only managing to attain an altitude of 16˚ when due south. Saturn fades this month, from mag. +0.6 on the 1st to +0.8 on the 30th. Through an eyepiece, its rings remain well presented, the northern pole tilted towards Earth by nearly 23˚. A waxing gibbous Moon sits 3.2˚ south on the evening of the 25th.
Best time to see: 30 September, 03:00 BST (04:00 UT) Altitude: 51˚
Uranus is well positioned this month, located in the southern part of Aries and not too far from Mars. It shines at mag. +5.7, making it theoretically visible to the naked eye from a dark-sky site. One problem with this is identifying where Uranus is as this area of sky is bereft of any easy to use navigational patterns. Binoculars are a sure way to see it, as is the use of a scope. Even a small aperture should reveal its green hue.
Best time to see: 11 September, 01:10 BST (00:10 UT)
Location: Aquarius Direction: South Neptune reaches opposition on the 11th when it can be seen in darkness all night long, shining at mag. +7.8, 2.1˚ east-northeast of mag. +4.2 Phi (ϕ) Aquarii. Opposition makes little difference to distant Neptune’s appearance in a scope, in contrast to a closer body such as Mars. Being below the threshold of naked-eye visibility, you’ll need at least a pair of binoculars to spot it. A scope will reveal the planet’s blue-coloured disc.
NOT VISIBLE THIS MONTH: