The top sights to observe or image this month
DON’T MISS: Partial solar eclipse
BEST TIME TO SEE: 25 October, 10:00 BST (09:00 UT) until 12:00 BST (11:00 UT)
CAUTION
Never observe or image the Sun with the naked eye or any unfiltered optical instrument
After what seems like ages since the last solar eclipse visible from the UK – a partial which took place on 10 June 2021 – we get the chance to see a partial eclipse on the morning of 25 October. Partial solar eclipses happen when, from a particular location on Earth, only part of the Sun’s disc is covered by the Moon’s disc. Technically, during such an eclipse, it’s the Moon’s penumbral shadow passing over us.
The amount of the Sun’s disc which is covered is described by two quantities: eclipse magnitude and obscuration. Eclipse magnitude describes how far the eclipsing body extends over the diameter of the object being eclipsed. For example, if the Moon’s edge reached the mid-point of the Sun at the point of maximum eclipse, this would be described as a partial eclipse of magnitude 50%; the Moon covers half the Sun’s apparent diameter. Eclipse obscuration describes how much area is covered. In our example, where the Moon moves to a position where its edge touches the centre of the Sun’s disc, the obscuration would be 39.1%, assuming the apparent diameter of the Sun and Moon were the same. In practice there are small differences between the apparent size of the Sun and Moon caused by the elliptical orbit of the Moon around Earth and the elliptical orbit of Earth around the Sun.
This partial solar eclipse favours those living further east and to a lesser extent, further north. For example, from Truro in Cornwall the event starts at 10:12 BST (09:12 UT) and ends at 11:38 BST (10:38 UT), a total duration of 86 minutes. The maximum magnitude of the Truro eclipse is 17.66% and obscuration is 8.65%. From Birmingham the eclipse starts at 10:07 BST (09:07 UT) and runs for 101 minutes, with maximum magnitude 25.65% and 14.95% obscuration. York’s starts at 10:06 BST (09:06 UT), lasts for 106 minutes, and shows a maximum magnitude of 29.29% and obscuration of 18.13%. From the northeast tip of Shetland it begins at 10:01 BST (09:01 UT), runs for almost two hours, shows a maximum magnitude of 40.96%, while the obscuration is 29.38%.
As this is a partial eclipse, appropriate filter protection must be used to keep your eyes and equipment safe. Certified eclipse glasses will show the bite taken out of the Sun well. Alternative low-tech visualisation methods include creating a pinhole or similar multi-holed projection setup. A pinhole in a piece of card can be used to cast a shadow onto a light surface, the light passing through the hole being a small image of the Sun. A metal tea strainer makes a surprisingly good shadow-caster for this purpose.
Thin Moon and Mercury
BEST TIME TO SEE: Morning of 24 October, from 07:00 BST (06:00 UT)
The visibility of the thinner crescent phases of the Moon is optimised around the equinoxes. Around the March equinox, it’s the waxing crescents that are well placed, the ecliptic making a steep angle with the western horizon at sunset. At this time of year, it’s the morning crescents that are optimally placed, the ecliptic making a steep angle with the eastern horizon around sunrise. The Moon never wanders that far from the ecliptic, its orbit being tilted by around 5˚ to the ecliptic plane.
On the morning of 24 October, the thin waxing crescent Moon rises above the eastern horizon 90 minutes before the Sun and will have a phase of 2%. It should be easy to spot as it rises, as the sky will still be relatively dark. Approximately 30 minutes after the Moon has appeared, Mercury will pop up above the same point on the horizon. At a magnitude of -1.0 and under brightening twilight skies, the planet should be easy to spot too. The pair will be 4.1˚ apart as they climb in altitude. From the centre of the UK, the Moon will attain an altitude of 6˚ and Mercury 3˚ at 07:15 BST (06:15 UT).
This thin Moon should look particularly attractive as it should be showing the phenomenon of ‘earthshine’, where the night side of the Moon appears to glow gently against the surrounding sky. The effect is caused by sunlight reflecting off Earth, hitting the Moon and reflecting back towards Earth. If you were standing on the Moon’s Earth-facing side in the nighttime portion, the Earth would appear almost full and around four times larger than the Moon appears in our sky. Being more reflective than the Moon also helps Earth bring light to the Moon’s nearside night.
Orionids 2022
BEST TIME TO SEE: Night of 21/22 October
The Orionid meteor shower peaks on the night of 21/22 October. The shower produces a peak zenithal hourly rate (ZHR) of 20 meteors per hour, this representing the number of meteors you would see under perfect conditions with the meteor shower radiant – the point in the sky from which the shower trails appear to come from – directly over your head. In reality, hardly any of these conditions are met and so the visual hourly rate, the number of meteors you’ll actually see, will be significantly lower than the ZHR.
Orionid meteors are the result of Earth passing through the orbital dust stream of comet 1P/Halley. The Orionids can produce good trails as long as you give yourself time to become properly dark adapted and spend a period of at least 30–60 minutes outside, looking up. This year an 11%-lit waning crescent Moon rises around 03:50 BST (02:50 UT) and shouldn’t cause too much of an issue.
Find a comfortable location away from artificial lights and with a clear horizon. Wrap up warm and look up at an altitude of around 60˚. Any direction will do, the south having some good constellations to enjoy. The radiant position is close to Betelgeuse, and trails near this point will appear shortest, while those 90˚ from this point appear longest.
