This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of October 2011.
October 2011 Highlights
* Draconid meteor shower may produce high rates over Europe and Asia on the 8th
* Jupiter is at opposition on the 28th
* Comet C/2009 P1 (Garradd) is a nice binocular object during the evening
* Orionid meteor shower peaks on the 21st
Note: If anyone has pictures or observations of these objects/events and want to share them with my readers, send them to the Transient Sky at <firstname.lastname@example.org>.
Mercury – Mercury spends the later half of the month in a poor evening apparition. Usually such a poor apparition wouldn’t be worth observing but this month Venus can be used to find Mercury. Use the Moon to find low but brilliant (magnitude -3.9) Venus and even lower and fainter (magnitude -0.3) Mercury on the evenings of October 27 and 28.
Venus – After spending the past month or so too close to the Sun to be observed, Venus is now starting its slow crawl into the evening sky. Its elongation from the Sun grows from 13° to 20° in October. Still you will need a clear view of horizon to catch Venus low in the WSW during early twilight. Use the Moon to find low but brilliant (magnitude -3.9) Venus and even lower and fainter (magnitude -0.3) Mercury on the evenings of October 27 and 28.
Jupiter - The King of Planets is the King of the Night Sky this month. With the other 4 naked eye planets hugging the twilight horizon or rather faint, Jupiter is by far the brightest and best placed. Rising a little over an hour after sunset on the 1st and right at sunset on the 31st, it is at its best around midnight. Opposition occurs on October 28 when Jupiter will peak in brightness at a magnitude of -2.9. For the entire month it will be slowly retrograding in the constellation of Aries. Not that you’ll need the Moon to find Jupiter but the two will make a nice pair on the nights of the 12th and 13th.
Mars - With opposition in March 2012, Mars continues to slowly brighten (magnitude +1.3 to +1.1) as it moved from Cancer into Leo this month. Mars rises after midnight and is best just before dawn. If you are out watching the Orionids, Mars will be the bright ruddy star near the Moon on the mornings of the 19th and 20th.
Saturn - Saturn passes conjunction on the far side of the Sun at mid-month (Oct 13). Those with very clear eastern horizons may be able to see Saturn an hour before sunrise by the end of the month. Saturn (magnitude +0.7) will be located ~5° to the lower right of the slightly fainter star Spica (magnitude +1.0).
Meteor activity is still near a seasonal high in October. The year is usually split in 2 with January through June having low rates with few major showers while July through December have high rates with many major showers.
Sporadic meteors are not part of any known meteor shower. They represent the background flux of meteors. Except for the few days per year when a major shower is active, most meteors that are observed are Sporadics. This is especially true for meteors observed during the evening. During October mornings, 10 or so Sporadic meteors can be observed per hour from a dark moonless sky. The Taurids should also contribute another 2-5 meteors per hour all night long.
Major Meteor Showers
Draconids (Giacobinids) (GIA) [Max Date = Oct 8, Max ZHR = highly uncertain between 50 and 600 per hour]
On October 8th at ~20 hours UT, the Draconid meteor shower may produce an outburst of meteors for observers in Europe and Asia. While normally a weak shower, the Draconids put on two of history’s best meteor storms in 1933 and 1946. In those years rates as high as 10,000 per hour were seen. More recently an outburst in 1998 produced a few hundred meteors per hour. This year the Earth will cross dust trails produced by Comet 21P/Giacobini-Zinner in 1900 and 1907, the same two trails that produced the 1933 and 1946 storms, as well as older trails back to 1866. Due to the older age and dispersion of these streams, a major storm is not possible this year. Still ZHRs as high as a few hundred per hour may be possible. The actual number of meteors seen by observers will be much less due to the nearly Full Moon. As a result, the shower may “only” appear as good as the Perseids or Geminids at their peak under a Moon-less sky.
If you’re like me and live in North America, well, we are probably out of luck. Chances are we will see little or no enhancement from the dust trail crossings. This will probably only be a good show for those in Europe, Asia and northern Africa. A map of visibility and much more information on this year’s shower cab be found at the International Meteor Organization’s (IMO) 2011 Draconids site.
Orionids (ORI) [Max Date = Oct 21, Max ZHR = ~35-45 per hour]
The Orionids are one of the most reliable and productive showers of the year. Another point in their favor is their high level of activity over the course of ~5 nights or so. This gives ample opportunity to catch a few Orionid meteors. This year the just past Third Quarter Moon will hamper meteor watching somewhat.
The meteors that make up the Orionid shower were originally released by the one comet everyone has heard of, Comet Halley. Computer simulations of the past movements of Halley and its dust suggest that many of this year’s Orionid meteors were released by Halley between 1265 BC and 910 BC (for some points of reference, the Trojan War took place around 1200 BC and King David ruled around 1000 BC).
The Orionids are usually active from Oct 3 to Nov 11 with a broad peak between Oct 18 and 24. During their peak, rates can be as high as 20-70 meteors per hour. During the last two years ZHRs reached 35-45 meteors per hour which is nearly half the rate observed in 2007 (70 per hour). This year’s activity should be similar to the last few years. With a Moon-lit sky, actual rates will be somewhat lower.
The Orionids appear to come from an area in northern Orion. This area, called the radiant, rises around 10pm local time. It is best to wait till the radiant is high in the sky before looking for meteors (say 1am). The radiant is highest around 3:30am which is the best time to look. As you can see on the sky chart, the Moon is almost on top of the radiant. Meteors can appear anywhere in the sky so you don’t have to look at the radiant.
Minor Meteor Showers
Minor showers produce so few meteors that they are hard to notice above the background of regular meteors. Info on many minor showers are provided on a weekly basis by Robert Lunsford’s Meteor Activity Outlook.
Additional information on these showers and other minor showers not included here can be found at the International Meteor Organization’s 2011 Meteor Shower Calendar.
Naked Eye Comets (V < 6.0)
None this month…
Binocular Comets (V = 6.0 – 8.0)
C/2009 P1 (Garradd)
The brightest comet of the year is long-period comet C/2009 P1 (Garradd). First seen way back on August 13, 2009 by Gordon Garradd who was observing for the Siding Spring Survey, a NASA-funded survey observing from Australia. At the time of discovery it was located at a distance 8.7 AU from the Sun, nearly the distance of Saturn. Perihelion will occur 2 days before Christmas 2011 at 1.55 AU from the Sun. Though the comet does not get very close to the Sun, it is an intrinsically bright comet and is already a borderline naked eye object for observers at very dark sites (6th magnitude).
The comet starts the month at a distance of 1.92 AU from the Sun and 1.70 AU from Earth. At mid-month it is 1.81 AU from the Sun and 1.87 AU from Earth and by month’s end it will be 1.72 and 2.01 AU from the Sun and Earth, respectively. Visual observers are placing the comet at magnitude 6.6 to 6.8 at the end of September. It should slightly brighten this month as it slowly moves west in Hercules.
Date RA DEC Delta r Elong Mag
Oct 1 18h 09m +19°23' 1.697 1.921 87 6.7
Oct 16 17h 49m +18°51' 1.866 1.811 71 6.6
Oct 31 17h 37m +18°44' 2.005 1.716 59 6.6
Small Telescope Comets (V = 8.0 – 10.0)
First seen in 1948 by Japanese amateur Minora Honda, Czech astronomer Antonin Mrkos and Slovak astronomer Ludmilla Pajdusakova, this comet is on its 11th observed return since discovery (it was missed during the 1959 and 1985 returns). It is an intrinsically faint Jupiter-family comet which passes within 0.53 AU of the Sun every 5.25 years. This time perihelion passage occurred on September 28. Prior to perihelion the comet made a close approach to within 0.06 AU of Earth which was only easily visible from the Southern Hemisphere. During the next return in 2016/2017, 45P will pass within 0.08 AU of Earth on its outbound leg and will be much better placed for northern observers.
Being after perihelion, the comet will rapidly fade as it moves away from the Sun and Earth as it moves through the constellation of Leo. At the start of the month, it should still be a binocular comet at magnitude 7.6 but will be lost to binoculars within a week or so. At an elongation of 32-37° it can only be seen low on the horizon before dawn.
Date RA DEC Delta r Elong Mag
Oct 1 10h 26m +08°27' 0.827 0.532 32 7.6
Oct 16 11h 17m +05°26' 1.139 0.641 34 9.9
Oct 31 12h 03m +01°40' 1.380 0.839 37 12.7