Watching out for falling stars

Tullamore Astro

Each year in the astronomical calendar (which runs pretty much the same as the fiscal one!) there are a few celestial events that spark great interest among those who enjoy astronomy. One such event is probably the most dedicated meteor shower for the last 3 centuries, The Perseids Meteor Shower. It is just like any other meteor shower, only this one has more significance to it.

That significance is the abundance of falling stars at its peak, without failure to show up, and always unleashing a few surprises. Surprises like fireballs – extraordinarily large meteors that will break up as they burn, with the lucky few making an audible sonic boom as it streaks through the atmosphere. And bursts of many seen within minutes, and sometimes seconds, of each other. While you can spot meteors on any clear night, have you ever wondered where they come from?


Back In Time
For that, lets have a brief history of the formation of the Solar System

We have to go back over 7 billion years to when the massive gas and dust cloud from whence we were formed began to collapse and take shape. At the centre of this spiralling mass was a very young star with its nuclear reactions producing heat and light for the first time. Encircling around it at different distances, clumps began to form in the disc of gas, dust and rock, and beyond them in the outer reaches where the star’s gravity was too weak to draw in debris or lend help in it producing a proper shape, a loose halo enveloped the system.

Around 5 billion years ago, the star’s energetic output steadied, the clumps encircling coalesced into larger, more defined bodies, and the halo was playing a balancing act between drifting into interstellar space and lightly being drawn in towards the star.

Today, we recognise this stellar ballet as the Sun, planets (Mercury, Venus, Earth, Mars, an Asteroid Belt, Jupiter, Saturn, Uranus, Neptune, and Pluto, among others), and the Oort cloud.

For the past couple billion years, things began to settle – almost all roaming debris either burned up in the Sun, or smashed into the planets, or themselves created little orbits of their own. Today, everything appears relatively quiet out there, and has its place in this balanced equation known as The Solar System.


That is, except for…
Comets and asteroids – large chunks of rock and ice loosely held together by their own gravity. Many of the known asteroids in the Belt between Mars and Jupiter are relatively inert fragments. The best theory for this existence is that it is the failed remains of a planetoid that may have begun to form, but was caught between the Sun’s gravity, and Jupiter’s gravitational pull. While space is cold, the Belt is relatively close to the Sun that most of the asteroids lost all their ice.

Further out, way beyond the orbit of Pluto lies a massive cloud, or halo, enveloping the entire Solar System, known as the Oort Cloud. Out here, it is very, very cold. The Sun appears simply as the brightest star in the sky. No heat reaches here, and it is almost at absolute zero (-273 degrees Celsius). Therefore, most the asteroids in this area are covered in ice.

Overtime, random ones are drawn in toward the Sun. As they close in and tumble along their way, they get warmer. And as they do, a process similar to melting a dirty snowball made from frozen carbon dioxide ice (“dry ice”) occurs – gases escape from within as the heat causes expansion and contraction of the asteroid. Soon, with the escaping gases, debris is lifted away – dust, ice, rock.

When this happens, it is recognised as a comet. Many comets pulled towards the Sun like this will simply collide harmlessly with the Sun. Some, disturbed by planets they may pass close to on their way in, become caught in orbits of their own. These are known as periodic comets. Some of the best known include Halley, West, Shoemaker-Levy, Encke, Wild-2, Schwassman-Wachmann, and many more.

The comet then gets brighter, and leaves behind it a tail of debris that will drift through space for millions of miles. Some comets drift past Earth’s orbit. But don’t worry, there are no foreseeable collisions by comets to happen yet for the next couple thousand years!

It is when Earth drifts through these tails of dust and rock that an increase in activity is noticed. Of course, random pieces of debris burn up all the time, but when Earth cuts through a tail, this increase, normally lasting only a couple of days at best, is called a Meteor Shower.


The Perseids
With the Perseids, it was the passing of a comet called Swift-Tuttle, so-called because it was discovered by 2 independent observers at the same time: Lewis Swift of New York, and Horace Parnell Tuttle of Massachusetts, in July 1862.

Swift-Tuttle has a period of 135 years. It last passed close to Earth in 1992, leaving behind a fresh dust tail. Thus, each year, we pass through this dust tail, and previous dust tails left behind by Swift-Tuttle, between July 20 to August 22. But the fireworks take place on August 12/13 each year, as this is when we pass through the densest part of the tail stream. What we see is a rise in shooting stars across the sky, particularly in the northeast. All you need is to wrap up warm and keep your eyes peeled. There will be a bright Moon this year to hinder all but the brighter meteors unfortunately.


TAS Lecture
To find out more, Tullamore Astronomical Society will host an open lecture night entitled “Comets & Meteors: What’s The Connection?” on Tuesday evening, August 8th, in the Presbyterian Hall, High Street, Tullamore (admission €2.00). TAS will look on the formation of comets, their relation to the formation of meteors, the different types, and how to look out for them, especially over the weekend of August 12. There will also be details outlining TAS’s Perseids Star-B-Q, a free to the public “bring your own food” event held each year, details of which are on the website www.tullamoreastronomy.com.


Seanie Morris, TAS Secretary

Flukey

Nice article, but I am surprised at the reference to "falling stars" which as we all know is not the case, without that fact being pointed out. Anyway, I suppose it is only a minor quibble. The Perseids should be increasing in frequency now. Unfortunately the moon is getting stronger too. We'll all be keeping our eyes peeled.:)

Snowbie

Saw a number of meteors about 3.30am radiating out from Perseus.Moon was not interfereing that much but would be nice if it were new moon rather than a gibbous.Roll on tonight,that cloud cover should break up.

Flukey

Tonight should be really busy. We are around the peak now. There have been quite a few over recent weeks, as posted about in the other threads relating to it that are here. I've seen a few myself. It is a pity about cloud cover when these highlights of the night skies come round. At least with showers, they carry on over a long period, so you have plenty of opportunities for clear nights, even if they are not on the night of the peaks.

Snowbie

Seen a good few now,cloud has rolled back in a bit now but still gaps in sky for viewing.