Peter Jenniskens, an astronomer at the AMES RESEARCH CENTER near Mountain View, California has identified 13 similar meteor streams that probably come from long-period comets, and he estimates that there might be as many as 70 such bodies that cross the Earth’s path at some point in their orbit. One such outburst is the Monocerotoid Shower (all meteor showers are named after the constellation from which they seem to radiate), which puts in an appearance each year in late November. Strangely, some years are more intense than others. Jenniskens theorizes that not only are meteor showers caused by the passage of comets, they are also influenced by the gravitational pull of the more massive planets such as Jupiter and Saturn which make the debris fields weave in and out of Earth’s orbit. Depending on the position of the planets, Earth may miss the debris field entirely, and at other times experience a particularly brilliant cosmic light show. Based on his calculations, he predicted that there would be such an event on November 22, 1995. Before that, the Monocerotoids had only put in appearances on 1925, 1935 and 1985. His diligence was rewarded: for 50 minutes on the morning of November 22, 1995, the sky loosed a torrent of meteors. By studying the trajectories of the meteors, he was able to determine that the orbit of this debris stream extended out ten times further than Pluto.
Monocerotids Radiant
This week there is an opportunity to observe a pretty interesting meteor shower known as the Alpha Monocerotids. Activity from this shower can be seen from around November 15 to 25 with the peak of activity expected to occur on November 21, 2008 at approximately 0925 hours UT (Source: IMO). Here are the particulars on this shower:
What makes this shower interesting is that it produces variable rates. The 5 listed above is what it normally produces, but it can go into overdrive and give observers a chance to see hundreds per hour as it did in 1995. That year the enhanced rates lasted less than an hour, so you have to be in the right spot at the right time. The IMO believes this
year the Americas are well placed for any extra activity. But of course, you will have to deal with the moon, which rises around 1 am. I personally do not like to observe under moonlit conditions, but if you take a look at the recent observations we have received, you’ll find it is still possible. (Source: Mark Davis – NAMN)
The swift-meteor α Monocerotids are usually a minor shower, active from November 15-25, with a maximum due this year at ~09:25 UT on November 21. In most years, their peak ZHR is around 5, but very occasionally, a much stronger outburst happens, when for a short while, their ZHR rises dramatically into the hundreds. The most recent such event was in 1995. Increased rates were seen across Europe then (including in the UK) for just 30 minutes, and estimated ZHRs peaked at 420 for a mere five minutes within that time. For that half hour, it was as if someone had turned on the Perseids during an autumn night, as the α Monocerotid meteors are similarly quick, albeit not as bright. There had been a suspicion that such enhanced activity might happen at ten-year intervals, but nothing unusual was detected during the moonlit decadal return in 2005, and the latest predictions by Finnish meteor analyst Esko Lyytinen suggest there may be no strong outbursts again till 2043, though there could be a weak event in 2019. So much for theory, but it is important to check the shower each year in case anything unexpected should transpire. The peak timing, if it proves accurate, will be useless for doing so this autumn from Britain unfortunately, and comes with a waning crescent Moon that will rise around 00:30 UT then anyway. This is problematic, since the shower’s radiant at the maximum, a few degrees southeast of Procyon, α Canis Minoris, as illustrated by the chart here, is well on-view only after 23h UT or so. Even so, the shower is always worth keeping an eye out for, just in case! (Source: Alastair McBeath)
