Astronomy Guide October 2023

Dear Stargazer Friends,

I hope you have been well. October is around the corner with many fascinating celestial phenomena to observe.

On the night of 20 – 21 October, the Orionid Meteor Shower will peak. The Moon will be 37% full. You’ll find more information below in the Topic of the Month “The Orionids and the origins of meteor showers”. Special thanks to Dr. Josep Trigo-Rodríguez his comments on this month’s topic.

October 2023 will also have an annular solar eclipse (14 October), as well as a partial lunar eclipse (28 October) in store. The annular solar eclipse will be visible from parts of North, Central, and South America. For more information visit NASA.

The partial lunar eclipse on 28-29 October 2023, will be visible, or at least partially visible from Europe, Asia, Australia, Africa, North and much of South America. During a partial lunar eclipse, only a part of the moon enters Earth’s shadow, which will appear dark on the side of the moon facing Earth. For more information on when to observe this phenomenon from your region, visit Timeanddate.com.

Planets Venus and Jupiter will be a great sight in the very early mornings. October is also an ideal time to observe Jupiter’s Galilean Moons – Io, Europa, Ganymede, and Callisto.

Daylight saving time ends on 29 October 2023, in Europe and on 5 November 2023, in USA and Canada.

Enjoy the journey & clear skies!
Isa 

The Orionid meteor shower will last from 28 September till 22 November, 2023, with the peak on the night from 20 – 21 October, 2023.

This month, I will briefly explain the origins of meteor showers, their classification, radiant and parent bodies as well as their value for scientists to better understand their origins and formation times.

When a meteoroid enters Earth’s atmosphere, it becomes an atmospheric phenomenon called meteor or a fireball. Cometary meteoroids like the Orionids are fragile aggregates and do not survive as meteorites, but asteroidal rocks with enough mass and producing bright fireballs sometimes do.

Meteoroids have a diameter range between 0.1 mm and < 10 m. “As meteoroids deepen in the atmosphere, they undergo continuous collisions with molecules in the stratosphere, which gradually heat up the surface of the meteoroid until the process of mass loss known as ablation begins.” (Trigo-Rodríguez 2022:5–8). Meteor showers are usually remnants of comets, although some asteroids also seem to produce them.

Trigo-Rodríguez (2022:4) classifies meteoric phenomena to their magnitude (m): a meteor has a magnitude between +6 < m < – 4; a bolide or fireball between – 4 > m > – 17, and a superbolide – a very rare phenomena such as the famous Chelyabinsk superbolide – m <- 17.

Meteors radiate from a specific point in the sky, called the radiant, and the event occurs when the Earth passes through a trail of debris left behind by a comet or asteroid. Meteor showers occur at regular intervals when Earth passes through the same region of space where the debris trail is concentrated. They vary in intensity, ranging from a few meteors per hour to hundreds during the peak time.

The Orionids meteor shower occurs annually when Earth passes through the debris left behind by Halley’s Comet. The meteors are named after the constellation of Orion, from where they seem to radiate – typically located near the red supergiant star Betelgeuse (also designated as Alpha Orionis). Earth’s orbit intersects with the debris trail of Halley’s Comet around mid-October each year. The particles enter the Earth’s atmosphere, creating meteors as they burn up due to the friction with the atmosphere.

The best time to observe the Orionids is during the pre-dawn hours when the radiant point is high in the sky.

As for Comet 1/P Halley, also referred to as Halley’s Comet, it is a periodic comet. It orbits the Sun in a predictable, elliptical path, returning to the inner solar system at regular intervals. It is particularly noteworthy because of its bright appearance and the fact that it is visible from Earth roughly once every 76 years. Due to the non-gravitational forces the period can “oscillate” a few years.

Comet 1/P Halley is the only known short-period comet regularly visible to the naked eye from Earth. It last appeared in the inner parts of the Solar System in 1986 and will next appear in 2061. It is named after the English astronomer Edmond Halley who understood in 1705 that the appearances observed around the world since ancient times were re-appearances of the same comet.

Meteor showers provide valuable insights into comets and the broader solar system. And, as Trigo-Rodríguez (2022:9, 14) writes: “Recovering meteorites is therefore a valuable scientific opportunity in many respects.” “They are samples from other worlds that, similar to terrestrial rocks, can impart immeasurable information about their origin and formation times.” If you are interested in meteorites and their parent bodies, I can highly recommend Dr. Josep Trigo-Rodríguez book, “Asteroid Impact Risk. Impact Hazard from Asteroids and Comets”.

Wishing you clear skies for the Orionids meteor shower – step outside and embrace the beauty of the night sky.

Sources and further reading:

• Trigo-Rodríguez, Josep M. (2022): Asteroid Impact Risk. Impact Hazard from Asteroids and Comets, Cham, Switzerland: Springer Nature. Link
• Wikipedia: “Betelgeuse” (visited on 25.9.2023).
• Wikipedia: “Halley’s Comet” (visited on 25.9.2023).
• ChatGPT