Derekscope

Algol Minima
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• The bright variable star Beta Persei (Algol) reaches its minimum brightness at 04:00 am in the early morning on Monday 15th December and will be visible from the UK.
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• Here’s a list of upcoming minimum brightness times for Algol – read more.
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• NGC 2420 known as a “twinkling comet cluster” and is a rich open cluster in Gemini, about 8,200 light-years away.
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• It’s not associated with comets, though its dense, glittering stars may poetically resemble a “twinkling comet cluster.”
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• Between Sunday 14th – Tuesday 17th December 2025, Jupiter remains over 3° south of NGC 2420, too far for a conjunction or close visual pairing.
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• This separation is significant – not close enough for binocular framing, though both are in Gemini.
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• The Geminid Meteor Shower reaches its peak on the night of 13th thru 14th December, with excellent viewing conditions this year.
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• The Moon, only 39% illuminated, will rise late around 23:30, providing minimal interference from moonlight.
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• Best viewing from mid-evening (after 9pm) through pre-dawn hours – the radiant is in the constellation Gemini, rising in the northeast.
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• Jupiter’s largest moon, Ganymede, will slip into Jupiter’s shadow at midnight, disappearing from view in telescopes.
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• This rare eclipse begins around 11:30pm on Saturday midnight – watch as Ganymede fades into darkness.
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• The Moon appears half-illuminated, with the left side 50% lit in the constellation Leo ~ it’s the final quarter of the lunar cycle, leading toward the New Moon on Saturday 20th December 2025.
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Titan & Rhea to be seen together

• Saturn’s moons Titan and Rhea are among its brightest satellites.
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• Titan is the largest, with a thick orange atmosphere, while Rhea is smaller and icy.
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• Titan and Rhea will be visible together near Saturn at 22:20 / 10:30 pm tonight, sometimes appearing side by side in telescopic views.
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• Their proximity is striking because Titan usually orbits farther out, while Rhea is closer in.

• The lunar occultation of Regulus on Wednesday 10 December 2025 will occur between 07:26 and 08:27 in the early morning, visible in the southwestern sky.
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• Regulus can be seen in daylight with a telescope but under very specific conditions.
  

Three Acts on Jupiter’s stage in one night!

• Monday 8th at 9pm
  Io slips into shadow, Callisto’s shadow centred on Jupiter.
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• Monday 8th at 10.30pm
  Callisto’s shadow leaves Jupiter as the Great Red Spot appears.
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• Tuesday 9th at 2.15am
  The Great Red Spot drifts away, and Callisto begins its transit.
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(Times above are shown to help you prepare for observing.)

Titan transits Saturn early evening

• Saturn is visible from the UK with a telescope.
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• The transit begins around sunset and continues into twilight, offering a rare and poetic view of Saturn’s largest moon crossing the planet’s disk.
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• Mercury reaches greatest western elongation on Monday 8th December 2025.
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• At this point, it will be 20.7° west of the Sun and best visible in the morning sky from the UK.
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• Best seen in the morning sky, rising about 90 minutes before sunrise ~ low in the eastern sky, just above the horizon (Mercury brightness ~ magnitude: -0.5).
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