Orionid Meteor Shower

Blog Credit: Trupti Thakur

Image Courtesy: Google

Orionid Meteor Shower

The annual Orionid meteor shower is set to light up the night sky in October 2023.

The Orionid Meteor Shower

• Annual Phenomenon:The Orionid meteor shower occurs every October as Earth passes through the debris left behind by Halley’s Comet, scientifically known as 1P/Halley.
• Comet Origins:Halley’s Comet, with dimensions of approximately five by nine miles, sheds dust particles from its nucleus during its solar orbit. This debris creates a trail that Earth intercepts, resulting in the Orionid meteor shower.
• Unique History:Halley’s Comet holds a special place in astronomy as the first comet to have its return predicted, thanks to the calculations by English astronomer Edmond Halley. Interestingly, the comet is named after its orbit calculator rather than its discoverer.

The 2023 Orionid Meteor Shower

• • Peak Dates:                The peak of the Orionid meteor shower is expected on the mornings of October 21 and 22 in 2023.
  • Moonlight-Free:      This year’s event promises to be particularly spectacular due to the absence of moonlight, enhancing the visibility of meteors.
  • Characteristics:      The Orionids are known for their speed and brightness, making them a favorite among stargazers.

A Glimpse of Halley’s Comet

• • Comet’s Size:             Halley’s Comet measures about five by nine miles in size and loses between three to ten feet of material on each passage through the inner solar system.
  • Predictable Returns:          Halley’s Comet has a unique history of predictable returns and has been observed throughout history, with recorded sightings dating back to 240 CE.

 

The Orionid meteor shower active from 2 October to 7 November, producing its peak rate of meteors around 22 October.

Over this period, there will be a chance of seeing Orionid meteors whenever the shower’s radiant point – in the constellation Orion – is above the horizon, with the number of visible meteors increasing the higher the radiant point is in the sky.

Seen from New Delhi , the shower will not be visible before around 22:01 each night, when its radiant point rises above your eastern horizon. It will then remain active until dawn breaks around 05:59.

The shower is likely produce its best displays in the hours around 05:00 IST, when its radiant point is highest in the sky.

At this time, the Earth’s rotation turns New Delhi 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 New Delhi, 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 06:00 IST on 22 October 2023.

Observing prospects

At its peak, the shower is expected to produce a nominal rate of around 15 meteors per hour (ZHR). However, this zenithal hourly rate is calculated assuming a perfectly dark sky and that the radiant of the shower is situated directly overhead. In practice, any real observing sight will fall short of these ideal conditions. The number of meteors you are likely to see is thus lower than this, and can be estimated using the ZHR formula.

From New Delhi, the radiant of the shower will appear at a peak altitude of 77° above your horizon, and on the basis of this, we estimate that you may be able to see up to 14 meteors per hour at the shower’s peak.

The Moon, in Sagittarius, will be around first quarter phase at the shower’s peak, but will set at 00:05 and pose no interference later in the night.

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 Orionid meteor shower is at around right ascension 06h20m, declination 16°N, as shown by the green circle on the planetarium above.

 

 

Blog By: Trupti Thakur