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Friday, May 15, 2020

Shooting Stars


When I prepared my previous posts earlier this month, I hardly expected there to be much interest in comets as there has been. I thought it would be a good topic to write about as I had some interesting postage stamps on Halley's comet and May is the month during which we are able to see the Eta Aquariids. This will be my last post on the topic of comets for a while so I hope to close off with a few stories and some (hopefully) interesting facts.

Shooting Stars

I promised myself to avoid too much astronomical jargon and to write something comprehensible for all readers so let's start with something that we all know or have heard about; "shooting stars". Exactly what is  a "shooting star"? In simple language, it is a meteoroid that enters the earth's atmosphere (after which it is then called a meteor).  As it plunges through the atmosphere, it vaporizes, the friction it encounters causing it to heat up and normally, it does not manage to reach the surface of the earth.  This is the ''shooting star" that we strive to momentarily observe.  If the meteor actually impacts the surface of the earth, it is then called a meteorite. 


There is still one item to outline further. We need to explain how a meteoroid originates. So, here goes. A meteoroid is a small rocky or metal object, as small as a grain of sand or a boulder that orbits the sun. It originates from a comet or an asteroid which invariably leave a trail of debris as they move through space on their orbital paths. If you wish to know more about comets or asteroids, please read my earlier posts.

Eta Aquariids and Orionoid meteor showers

I mentioned the Eta Aquariids earlier in this post. Now it is the time to return to this topic. We have mentioned in a previous post that Halley's comet orbits the sun every 75-76 years. Our earth, on the other hand,  orbits the sun every 365.25 days. Twice a year, the orbit of earth intersects the orbital path of Halley's comet. During those periods, when our planet makes those intersections, we encounter debris (i.e. meteoroids), that Halley's comet has left behind during its many journeys to and from the sun every 75-76 years. As these meteoroids encounter and plunge through our atmosphere, they become meteors  and we are able to observe meteor showers ("shooting stars''). 

Our planet encounters these meteoroids  in late April to the mid of May and in October each year. The meteor shower which peaks in early May is called the Eta Aquariids because it appears to an earth-based observer to originate (i.e. it has its ''radiant") from the constellation of Aquarius whilst, the meteor shower which peaks in October, creates the Orionid meteor shower as it appears to have its radiant from the Orion constellation. 

Other comets are also responsible for meteor showers or shooting stars. As an example, the "Southern Delta Aquariids" (which are visible from mid July to mid August each year)  originated from the break-up of the what are now the Marsden and Kracht Sungrazing comets. 

Stamps from Sri Lanka and Australia

The island of Sri Lanka, in the Indian Ocean, issued a series of stamps to mark the return of Halley's comet in the mid-eighties. I like this particular stamp as it clearly shows the orbit of earth, intersecting the orbital path of Halley's comet which then gives us the Eta Aquariids and Orionoid meteor showers. Australia also issued a stamp showing the same data.

Gifts of Halley's comet

Both the Eta Aquariids and the Orionid meteor showers are 'gifts' of Halley's comet that we are able to observe each year as a reminder of the comet itself which is racing around the Solar System. There is one more gift of Halley's comet that I personally like a great deal. I studied for my undergraduate degree at Bath University. In Bath, there is an artisan area called Walcot Street and in a house on that street once  lived (and died, in 1772) Samuel Scott, a celebrated English landscape artist. Whilst he is known for many maritime paintings, my particular favourite is shown below: 

This painting is called 'Return of Halley's Comet 1759'. 

Halley's comet can clearly be seen in the sky above the River Thames, its reflection majestically lightning up the water and waves of the river.

A stamp from the Cook Islands

A special moment in time, captured in a painting by an artist who died in 1772 shows the same scene issued on a postage stamp to commemorate the return of the same comet more than two hundred years later. History, geography, astronomy and art, all converging into a story brought to all of us by a mere (?) postage stamp!

Comet Kohoutek

I will close off this section on comets with a short story about how I came to know about the existence of these space nomads. In 1973, I was fifteen years old and I recall my father telling me that a Czech astronomer, L. Kohoutek, had discovered a new comet which would be visible from earth with the naked eye.Before its close approach, Kohoutek was promoted by the media as the "comet of the century".

At that time our family lived in Penang, a beautiful island in Malaysia. I did not much about comets was but I spent a little time doing some background research.

One of the highest points in Penang Island is Penang Hill at 833 meters above sea level. The only way up (at that time) to its peak was by funicular railway. My research told me that the peak of Penang Hill  would be a great vantage point to get an outstanding view of the approaching comet of the century. At my behest, my father agreed to take the family up the hill a particular Sunday evening to sight the comet as dusk approached. On the designated day, we went up the hill but comet Kohoutek hardly made a visual impression. In fact, Kohoutek's display was considered a let-down not only by our family but by many media commentators as well.  Comet Kohoutek was observed by the crews of Skylab 4 and Soyuz 13 and it thus became the first comet to be observed by manned spacecraft,.

A stamp from Gambia

A stamp from Gambia commemorates comet Kohoutek being observed by Skylab 4.

All stamps shown above are from my personal collection and were photographed using a HUAWEI P30 telephone / camera.

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