Wednesday, September 1, 2021Sunday, September 26, 2021

September 2021 – What’s Up!

Astronomical twilight ends at 20:45 BST at the start of the week and at 20:31 BST by the end of the week
Saturn (+0.5) and Jupiter (-2.7) continue to dominate our southern night sky and are perfectly placed for observation this week. Watch the transit of Jupiter’s moon, Io and its shadow on Wednesday evening; the transit commences at 18:55 BST and finishes at 21:15 BST
The Moon is Last Quarter on Wednesday
The Sun currently has 2 active regions: AR2871 and AR2872. The sunspot number is 38
The ISS makes multiple visible evening passes this week as follows:
Monday: 20:51, W to S, max 73°
Tuesday: 20:03, W to ESE, max 86° & 21:40, W, max 20°
Wednesday: 19:16, W to E, max 87° & 20:53, W to SSW, max 44°
Thursday: 20:06, W to SE, max 58° & 21:43, W to WSW, max 12°
Friday: 19:18, W to ESE, max 73° & 20:55, W to SSW, max 23°
Saturday: 20:08, W to SSE, max 32°
Sunday: 19:21, W to SE, max 43° & 20:59, WSW to SSW, max 11°

Astronomical twilight ends at 21:03 BST at the start of the week and at 20:48 BST by the end of the week
The Autumn Equinox occurs on Wednesday. At 20:21 BST the Sun will cross the Celestial Equator, heading south. This marks the start of autumn here in the Northern Hemisphere. There will be almost exactly 12 hours of night and day across our planet
It is currently possible to spot five planets: Venus (mag -4.1) is setting low in our western evening sky, Saturn (+0.4) and Jupiter (-2.8) are high through the night, transiting at around 22:00 BST, Neptune (+7.8) follows further east and Uranus (+5.7) rises at 20:24 BST. For a sixth solar system planet, look to your feet to add Earth to the list!
The Moon is Full on Tuesday – the Harvest Moon
The Sun currently has 1 active region: AR2871. The sunspot number is 11
The ISS makes multiple visible evening passes this week as follows:
Monday: 19:54, SW to E, max 31° & 21:30, WSW, max 49°
Tuesday: 20:43, WSW to E, max 72° & 22:20, W, max 14°
Wednesday: 19:56, WSW to E, max 58° & 21:33, W, max 44°
Thursday: 20:46, W to E, max 87° & 22:23, W, max 12°
Friday: 19:59, WSW to E, max 86° & 21:36, W, max 35°
Saturday: 20:49, W to E, max 87°
Sunday: 20:02, W to E, max 84° & 21:39, W, max 27°

Astronomical twilight ends at 21:22 BST at the start of the week and at 21:06 BST by the end of the week
Neptune reaches opposition on Tuesday, when it will be opposite the Sun as seen from Earth. It will be best placed for observation, appearing at its brightest, though still faint at mag +7.8, so binoculars or a telescope will be needed to see the planet. Look southeast in the constellation of Aquarius through the evening
Saturn (mag +0.4) and Jupiter (-2.8) continue to dominate our evening skies. They will be joined by the waxing Gibbous Moon towards the end of the week
The Moon is First Quarter on Monday
The Sun currently has 5 active regions: AR2863, AR2864, AR2866, AR2868 and AR2869. The sunspot number is 93
The ISS makes multiple visible evening passes this week as follows:
Thursday: 21:27, SW to SSW, max 14°
Friday: 20:41, SSW to SSE, max 23°
Saturday: 19:57, S to ESE, max 17° & 21:32, WSW to SW, max 31°
Sunday: 20:47, SW to ESE, max 46°

Astronomical twilight ends at 21:42 BST at the start of the week and at 21:25 BST by the end of the week
On Thursday evening, spot the 3 day old waxing Crescent Moon just under 7° from Venus (mag -4.1) as they set in the West. Look just after sunset, which is at 19:34 BST
Jupiter (-2.8) and Saturn (+0.3) are well placed in our evening skies
With little to no moonlight, this week is the perfect opportunity to observe M27, the Dumbbell Nebula, a planetary nebula in the constellation of Vulpecula, just below Cygnus. At mag +7 and only 8 arcminutes in size, you will need a good pair of binoculars or a telescope to find it
The Moon is New on Tuesday
The Sun currently has 5 active regions, AR2863, AR2864, AR2865, AR2866 and AR2867. The sunspot number is 68
There are no visible evening ISS passes this week

in What's Up