Find out what to observe in the night sky every month in our Star Diary podcast<\/a>, or prepare for the dark months ahead with our guide to autumn astronomy<\/a>.<\/strong><\/em><\/p>\n In September 2021, Neptune is located in Aquarius, roughly midway between mag. +4.2 Psi (\u03c6)<\/span> Aquarii and mag. +5.5 20 Piscium.<\/p>\n Binoculars will show it to look exactly like a mag. +7.8 star, but its planetary nature becomes more evident through the eyepiece<\/a> of a telescope.<\/p>\n Neptune shows a tiny 2 arcsecond disc. A power of 200x or greater is recommended to show this disc well.<\/p>\n The planet\u2019s colour, like the green hue of Uranus, is quite striking, Neptune being noticeably blue.<\/p>\n Neptune reaches opposition<\/a> on 14 September<\/strong> although being so distant, this optimal position in the sky doesn\u2019t make a great deal of difference to the planet\u2019s overall appearance.<\/p>\n It does mean it\u2019s up all night long though, so this is as good a time as ever to look for it.<\/p>\n Smaller instruments will show the planet\u2019s blue disc as described, but may also be able to pick out Neptune\u2019s largest moon, Triton.<\/p>\n Shining at mag. +13.5, Triton is an easy catch for a 300mm instrument, but isn\u2019t out of range of smaller scopes; 200mm is probably the minimum.<\/p>\n Larger scopes fitted with specialist high-resolution imaging kit may occasionally pick out large detail on Neptune\u2019s disc such as atmospheric banding and storm systems.<\/p>\n Mercury<\/a> is an evening object during September 2021, but its position deteriorates over the month. Your best chance of spotting it will be on 1 September<\/strong> when, shining at mag. 0.0, it sets 30 minutes after the Sun, below the western horizon.<\/span><\/p>\n This<\/span> doesn\u2019t give you long to locate it. Venus is also low in this direction, 16\u02da east of Mercury\u2019s position. By the end of the month, mag. +1.5 Mercury virtually sets with the Sun.<\/p>\n Venus<\/a> is visible in the evening sky after sunset, appearing higher than Mercury and much brighter. At the start of September<\/strong> Venus shines at mag. \u20134.0. By the end of the month<\/strong> it increases in brilliance to mag. \u20134.2. Venus sets approximately 1 hour after the Sun throughout the month.<\/p>\n Given a flat west-southwest horizon, it may be possible to spot Spica (Alpha (\u03b1<\/span>) Virginis) 1.6\u02da below Venus on the evening of 5 September<\/strong>.<\/p>\n Shining with a magnitude of +1.8, Mars<\/a> isn\u2019t really a viable target this month as it is too close to the Sun to be seen.<\/p>\n Jupiter<\/a> is an evening planet, managing to achieve its highest position in the sky due south in darkness during the month. It\u2019s apparent position in the sky has it travelling west through the eastern part of Capricornus, the Sea Goat and this will reduce its overall altitude over the month.<\/p>\n On 1 September<\/strong>, from the centre of the UK, Jupiter attains an altitude of 22.9\u02da. By 30 September<\/strong>, this value will have dropped to 22.0\u02da.<\/p>\n Being at opposition at the start of August and with the rapidly expanding nights that occur during September, Saturn<\/a> remains nicely placed, able to attain its maximum altitude of around 18\u02da from the centre of the UK under dark sky conditions all month long.<\/p>\n On 1 September<\/strong>, mag. +0.3 Saturn reaches its highest point in the sky, due south, at 23:10 BST (22:10 UT). By the month\u2019s end<\/strong>, this position is reached at 21:10 BST (20:10 UT).<\/p>\n![\""Imagine\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2020\/08\/Observe-Neptune-September-2021-d52ac78.jpg?quality=90&resize=620%2C461"\" "\\"\"Observe\\"")
<\/div>![\""Neptune\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2019\/08\/Planet-Neptune-98b9c5f-e1604308755157.jpg?quality=90&resize=620%2C429"\" "\\"\"Neptune\\"")
<\/div>How to see the planets in September 2021<\/strong><\/h1>\n
![\""A\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/25\/2020\/08\/Planets-September-2021-d0b5c6d.jpg?quality=90&resize=620%2C207"\" "\\"\"Planets\\"")
<\/div>Neptune<\/strong><\/h2>\n
Mercury<\/strong><\/h2>\n
Venus<\/strong><\/h2>\n
Mars<\/strong><\/h2>\n
Jupiter<\/strong><\/h2>\n
Saturn<\/strong><\/h2>\n
Uranus<\/strong><\/h2>\n