The December φ-Cassiopeid meteor shower will be active from 1 December to 8 December, producing its peak rate of meteors around 5 December.
Over this period, there will be a chance of seeing December φ-Cassiopeid meteors whenever the shower's radiant point – in the constellation Andromeda – is above the horizon.
From Ashburn , the radiant point is above the horizon all night, which means that the shower will be active throughout the hours of darkness.
The shower is likely produce its best displays in the hours around 21:00 EST, when its radiant point is highest in the sky.
At this time, the Earth's rotation turns Ashburn to face optimally towards the direction of the incoming meteors, maximising the number that rain vertically downwards, producing short trails close to the radiant point. At other times, there will be fewer meteors burning up over Ashburn, and they will tend to enter the atmosphere at an oblique angle, producing long-lived meteors that may traverse a wide area of the sky before completely burning up.
The shower is expected to reach peak activity at around 18:00 EST on 5 December 2020.
The Moon, in Leo, will be around last quarter phase at the shower's peak, but will only rise at 07:11.
The origin of the shower
Meteor showers arise when the Earth passes through streams of debris left behind in the wake of comets and asteroids. Over time, the pieces of grit-like debris in these streams distribute themselves along the length of the parent object's orbit around the solar system.
Shooting stars are seen whenever one of these pieces of debris collides with the Earth's atmosphere, typically burning up at an altitude of around 70 to 100 km.
On certain days of the year the Earth's orbit passes through particularly dense streams, associated with comets or asteroids which have vented particularly large amounts of solid material to space, and this gives rise to an annual meteor shower. Such showers recur on an annual basis, whenever the Earth passes the particular point in its orbit where it crosses the particular stream of material.
The meteors that are associated with any particular meteor shower can be distinguished from others because their paths appear to radiate outwards from a common point on the sky, which points back in the direction from which their orbital motion brought them.
This is because the grit particles in any particular stream are travelling in almost exactly the same direction when they cross the Earth's orbit, owing to having very similar orbits to the parent object they came from. They strike the Earth from almost exactly the same direction, and at the same speed.
To see the most meteors, the best place to look is not directly at the radiant itself, but at any dark patch of sky which is around 30–40° away from it. It is at around this distance from the radiant that the most meteors will be seen.
By determining the position of this radiant point on the sky, it is possible to work out the orbit of the stream giving rise to any particular meteor shower. It is sometimes even be possible to identify the particular body responsible for creating the debris stream, if there is a known comet or asteroid with a very similar orbit.
The radiant of the December φ-Cassiopeid meteor shower is at around right ascension 01h30m, declination 50°N, as shown by the green circle on the planetarium above.
|The sky on 05 December 2020|
20 days old
All times shown in EST.
The position of the radiant of this shower, and its predicted hourly rate, were taken from International Meteor Organisation's List of Meteor Showers.
© Jacek Halicki 2016. Perseid meteor seen in 2016 from Poland.