Archive for the ‘Meteors’ Category

Meteor/fireball on March 3rd

Posted: March 4, 2012 in Meteors, NASTRO

A wonderful night of observing at Hauxley Observatory last night.  I went with goal of getting some reasonably good pictures of the planet Mars.  But the highlight came at 9.41pm during a brief spell outside the observatory.  We all saw a bright meteor (a fireball) streaking across the sky from north to south.  Video footage here.  It was widely seen by people right across the UK.  It put me in mind of footage I’ve seen of an asteroid skimming the upper atmosphere and heading back into space.  Hopefully enough people captured this event on video or in pictures for the orbit of the object to be derived (and the possible trajectory after it disappeared).

Although it was bright (estimates I saw placed it at magnitude -9) it was probably only a metre or so in size (perhaps larger if if was made of icy material).  The slow moving appearance of the meteor was a combination of its distance and slow speed relative to us.  By slow, I mean it was probably moving at 10-20 km/s relative to us.  Since meteors typically occur at 60-120km above the ground, and this one wasn’t that high in the sky, it was actually hundreds of kms away from us at closest approach.

I’m done speculating on this until more data is available.

Death of a giant comet

Posted: November 12, 2011 in Astrobites, Comets, Meteors

The Northern Taurid meteor shower reaches a peak on November 12th.  For many amateur astronomers the month of November is associated with the Leonid meteor shower – a much more famous shower which has occasional stormy outbursts.  But I have to say, I prefer the Taurids because they have a more interesting backstory!

About 20,000 or 30,000 years ago a huge comet – perhaps 50km in diameter or more – became embroiled in a series of close approaches to the planet Jupiter.  Nothing unusual here – Jupiter has a huge family of comets even today.

For this ancient giant comet, the increased solar heating of its large surface area would have made a spectacular sight in the night sky for our ancestors.  The new orbital period – a few years, rather than decades or centuries – subjected this giant ice-world to intense levels of activity.   The rapid pace of the comet going around the Sun also accelerated its demise and it split into fragments, each of which would have made dramatic comet.  As the centuries rolled by each fragment may have split further or simply had its volatile surface materials boiled away into space – leaving, to all intents and purposes, an object resembling an asteroid.

These days, all we have left of the original giant progenitor comet are a small, faint comet with an orbital period of 3.3 years (called Encke’s Comet), a few small asteroids and a complex series of dust streams which the Earth encounters in November each year.   The dust released by the original comet and its subsequent fragments over periods of thousands of years have gradually been spread out into a broad swathe of the inner solar system.  Actually, the Earth also encounters one of the streams during June but during the daylight hours.  It is speculated that the devastating Tunguska event of 1908 was due to a larger fragment disintegrating in the Earth’s atmosphere.  That’s another story.

On Earth, each November, we see the remains of this giant comet, streaking into our atmosphere as a shower of shooting stars and appearing to come from the constellation Taurus.  It takes the Earth weeks to cross these lanes of dust and in doing so we encounter two distinct peaks – evidence of the complex evolution of the meteor orbits.  So in November we see the Northern Taurids and the Southern Taurids.  Activity is fairly low – typically about seven or eight per hour.  Compare this to, say, the short sharp spike in activity of the Perseids in August or the Geminids in December.

Will we see another giant comet? An intriguing object called Chiron, initially thought to be an asteroid, was discovered in 1977.  It orbits the Sun from within the orbit of Saturn to just beyond Uranus.  Later observations showed it to be developing a coma as it approached its nearest point to the Sun.  Chiron seems to be a giant comet  – perhaps 180km in diameter.  Mathematical modelling showed that the orbit it follows is unstable and chaotic over long periods; in a million years it will probably have been put into a completely different orbit within the solar system or perhaps ejected completely the neighbourhood.  It’s not out of the question that Chiron will one day be a spectacular giant comet gliding regularly through the inner solar system.

For further scientific reading see here.

Possibly the least observed meteor shower of the autumn will be the ε (epsilon) Geminids which reach a peak of activity on Tuesday night – the 18th/19th.  These are not the “Geminids” that astronomers get excited about every December! If you’ve been out observing during late October evenings then it’s possible that you’ve seen a meteor from this shower already; records show that the Earth encounters the meteor stream from about October 10th to the 27th.

Under perfect conditions (no moonlight, radiant directly overhead, etc) then 1 or 2 meteors per hour can be expected!  From the UK  the radiant can never be overhead and in 2011 the gibbous moon is near the radiant of the shower…so observed rates will be much lower than 1 or 2 per hour.  Also, the Orionid meteor shower (peaking on the 20th/21st) has a radiant nearby so meteors coming from that part of the sky may not necessarily be ε-Geminids.

Before you give up on this as a lost cause it’s worth noting that the ε Geminids were probably discovered by local astronomer Thomas William Backhouse (1842 – 1920).  That he was able to ascribe a radiant to meteors of such low frequency occurring close to the radiant of the Orionids is evidence of his meticulous observing skills.  Backhouse of Sunderland was a renowned visual observer in the late 19th and early 20th century.  He was one of the first astronomers to see Noctilucent Clouds and he brought the Gegenschein (a glow of zodiacal light directly opposite the Sun) to the attention of astronomers in the UK.  The northeast of England can claim a couple of well known astronomers as its own; Sir George Biddell Airy (born in Alnwick) went on to become a mathematician and the 7th Astronomer Royal.  And we adopted Sir William Herschel for the brief period he lived in Sunderland (although to be fair, he wasn’t an astronomer at this point.  Straws are being clutched.)  The contributions of T W Backhouse are numerous but he now seems to be the forgotten astronomer of the Northeast.

Back to the epsilon Geminids.  As the name suggests, the radiant is close to the star epsilon Geminorum in the constellation Gemini.  See a map here.  This year the waning gibbous moon (with 63% phase) is close to the radiant making observation tricky.  Higher rates will be seen after midnight – particularly in the hours leading up to dawn when the radiant is high above the southern horizon.  Don’t hold your breath though.