In The Sky This Month – October 2009
October 1, 2009 36 Comments
This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of October 2009. Jupiter continues its reign as not only king of the planets but king of the evening sky. October also brings the Orionids, one of the year’s better meteor showers.
Note: If anyone has pictures or observations of these objects/events and want to share them, send me a comment and I’ll post them on the blog.
Jupiter – Jupiter continues to dominate the evening sky. Based on the comments left on this blog, many people have been noticing Jupiter in the southeast sky during the evening. At magnitude -2.6, Jupiter is ~11 times brighter than the brightest stars in the sky this month. Of all the planets, only Venus, and on very rare occasions Mars, are brighter.
Jupiter is located high in the southern sky by the end of dusk for easy observation. As has been the case all year, it is slowly moving through the southern constellation of Capricornus.
Oct 27 – Moon passes 3° from Jupiter
Neptune – For those with a telescope or binoculars and a dark sky, Neptune is located within 1/2 to 3/4 degrees of Jupiter. Jupiter will be a bright magnitude -2.6 while Neptune will be a faint +7.9. That makes Jupiter over ~16,000 times brighter than Neptune. Even Jupiter’s 4 large Galilean moons are about a dozen times brighter than Neptune even though they are much smaller. The big reason for the faintness of Neptune is its distance from both the Earth and Sun. It is roughly 6 times further away from us and the Sun as Jupiter. The distance also explains its apparent small size of 2.3″. A good sized telescope will be required to see Neptune as anything other than a faint star.
Though Neptune wasn’t discovered until 1846, it was actually observed by Galileo on two occasions in 1612 and 1613. Similar to this month’s circumstances, Jupiter was passing very close to Neptune. Galileo observed and recorded Neptune as a star in the vicinity of Jupiter. There is also evidence that he noticed that Neptune had moved but didn’t follow up on it. So when you observe these 2 planets imagine what Galileo must have been thinking nearly 400 years ago.
Uranus – This month Uranus is a month past opposition and still near its maximum in brightness. Uranus is located in western Pisces and is bright enough to be seen in small binoculars at magnitude +5.7 but will still require a telescope in order to see it as anything other than a star (it’s disk is only 3.5″ across).
Mars – Mars can be seen in the eastern sky during the 2nd half of the might. It rises around midnight though it won’t get high enough to clear most trees and building till about 1-2 am. Mars is rapidly brightening from magnitude +0.9 to +0.6, its brightness matching that of many of the brightest stars visible in the morning sky. Mars will continue to brighten as it approaches its opposition on Jan 29 of next year. This month Mars marches through eastern half of the constellation of Gemini into Cancer. By Halloween, the planet will be moving through the Beehive, a big bright star cluster in Cancer.
Oct 12 – Moon within 1.1° of Mars
Venus – Venus rises an hour before dawn. When it is visible it is easily the brightest “star” in the sky. It was at its highest in the morning sky back in August and is continuing its slow crawl lower. For binocular and telescope users, Venus will appear nearly full and is much smaller than it appeared this spring (now 11″ across versus 50″ last spring).
Oct 13 – Saturn and Venus within 0.5° of each other
Oct 16 – Moon passes 6° from Venus
Mercury – Mercury puts on its best morning show of the year for northern observers. Below the equator, this is one of Mercury’s worst displays and probably worth skipping. For the 1st 3 weeks of the month, Mercury will be visible about 30 minutes before the start of dawn in the evening sky. The dates below highlight some of the best mornings to observe Mercury.
Oct 6 – Mercury furthest above eastern horizon at dawn
Oct 8 – Saturn and Mercury within 0.3° of each
Oct 17 – Moon and Mercury within 7° of each other
Saturn – After spending the last month or so too close to the Sun to be seen, Saturn is once again visible. Located in Virgo at magnitude +1.0, Virgo only rises right before the start of dawn. For those of you lucky enough to be up every morning and have access to a clear eastern horizon, October will provide a month long show as Venus, Mercury and Saturn dance among themselves. Telescope users should note that Saturn’s rings are still close to edge-on.
Oct 8 – Saturn and Mercury within 0.3° of each
Oct 13 – Saturn and Venus within 0.5° of each other
Oct 16 – Moon and Saturn within 6° of each other
October hosts one of the best meteor showers of the year in the Orionids. In addition, the background rate of meteors is near an annual high. The year is usually split in 2 with January through June having low rates with few major showers while July through December (really through the 1st week of January) 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 September, 12 or so Sporadic meteors can be observed per hour from a dark moonless sky.
Major Meteor Showers
Orionids (ORI) [Max Date = Oct 22, Max Rate = ~20-70 per hour]
The Orionids are one of the most reliable and productive showers of the year. Another point in their favor, is there high level of activity over the course of about 5 nights. This gives ample opportunity to catch a few ORI meteors.
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. Last year rates reached 39 meteors per hour which is nearly half the rate observed in 2007 (70 per hour). With no Moon in the sky, the sky will be nice and dark this year.
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.
More can be found at an earlier Orionid posting.
Minor Meteor Showers
Minor showers produce so few meteors that they are hard to notice above the background of regular meteors. Starting this month, info on most of the minor showers will be provided on a weekly basis by Robert Lunsford’s Meteor Activity Outlook.
Naked Eye Comets (V < 6.0)
Binocular Comets (V = 6.0 – 8.0)
Small Telescope Comets (V = 8.0 – 10.0)
Comet C/2006 W3 (Christensen)
This comet was discovered nearly 3 years ago on 2006 November 18 by Eric Christensen of the Catalina Sky Survey north of Tucson. At the time the comet was located 8.7 AU from the Sun which is nearly the distance of Saturn.
The comet reached perihelion at a rather distant 3.12 AU from the Sun on 2009 July 6. Because of its large perihelion distance, the comet will only slowly move away from the Sun and, though it will slowly fade, it should remain bright enough to be seen in modest sized backyard telescopes this month.
At mid-month, the comet is 3.3 AU from the Sun and 3.2 AU from Earth. Though observed as bright as magnitude ~8.2 it is now around magnitude 8.8. It is moving southeast while paralleling the summer Milky Way. This month the comet can be found in southern Aquila and is well placed for evening observing.
P/Howell is another evening comet and should be just as bright as C/Christensen. Howell is a short-period comet and takes only 5.49 years to orbit the Sun. Ellen Howell was a student at CalTech when she found the comet on photographic plates taken on 1981 August 29 with the 48″ Palomar schmidt.
In 1981 the comet was on a orbit that never brought it closer to the Sun than 1.62 AU (perihelion distance). As a result, it never got very bright. A relatively close approach to Jupiter in 1990 changed its perihelion distance to 1.40 AU. Further perturbations by Jupiter have decreased its perihelion distance to 1.36 AU. The closer perihelion distance allows the comet to get bright enough for small backyard telescopes.
This year the perihelion occurs on Oct 12 when it will shine at ~9.0 magnitude or maybe even a little brighter. The comet is located low in the southwest sky after dusk where it will start the month in the constellation of Scorpius before traversing Ophiuchus and ending the month in Sagittarius. At mid-month P/Howell will be 1.36 AU from the Sun and 1.65 AU from Earth.
217P/LINEAR is also a short-period comet though it takes a little longer than Howell to circle the Sun, 7.83 years versus 5.49 years. P/LINEAR also comes closer to the Sun with perihelion at 1.22 AU from the Sun. The comet is already a month past perihelion which occurred on Sept 8.
P/LINEAR was first observed by the Lincoln Near Earth Asteroid Research (LINEAR) survey on 2001 June 21 though it wasn’t until 2001 July 11 that it was recognized as a comet. The 2009 apparition is the first return since the discovery apparition.
Though P/LINEAR and P/Howell have similar perihelion distances, LINEAR is a much fainter (or less active) comet. While Howell is ~9th magnitude at a rather distant 1.65 AU from Earth, P/LINEAR is a little fainter at magnitude ~10.0 though it is much closer (0.61 AU from Earth). This may be the last time to see P/LINEAR in small backyard telescopes until its 2048 return when it will pass within 0.40 AU of Earth. All the returns between 2009 and 2048 will be more distant.
I was able to observe 217P/LINEAR with 30×125 binoculars on the morning of Sept 25. In order to see the comet I had to drive out to a dark site. The comet was a rather non-descript smudge about 1.5′ across and with a brightness of magnitude 10.1.
This month the comet will be visible in the morning sky moving from southern Orion into the faint Milky Way constellation of Monoceros. It should remain at magnitude ~10 for the entire month.
Comet C/2007 Q3 (Siding Spring)
After 2 short-period comets, this next comet is of the long-period variety. Comet C/2007 Q3 (Siding Spring) was first seen on 2007 August 25 by Donna Barton of the Siding Spring Survey in Australia. This Oct. 7 the comet will reach its rather distant perihelion at 2.25 AU from the Sun. Unfortunately, the comet and Earth are located on opposite sides of the Sun (a 3.0 AU distance). Still the comet may be observable during the 2nd half of the month right before the start of dawn as a ~9.5 to 10.0 magnitude comet in Leo.
A finder chart for Comet Siding Spring can be found at Comet Chasing and Aktuelle Kometen (in German).
Binocular and Small Telescope Asteroids (V < 9.0)
Juno was the 3rd asteroid to be discovered after (1) Ceres and (2) Pallas. It was found by German astronomer Karl Harding on September 1, 1804. With dimensions of 320×267×200 km (192 x 160 x 120 miles) Juno ranks as the 10th largest asteroid in the Main Belt though it is the 2nd largest stony S-type asteroid.
This month it will be moving slowly southwestward in Aquarius. Peak brightness occurred at opposition on Sept. 22 when Juno was as bright as magnitude 7.6. In October it will fade from magnitude 7.8 to 8.4. Twenty degrees or so to the east of Juno is another bright asteroid, (18) Melpomene which is described in its own section.
About 25 degrees to the east of (3) Juno lies another nice asteroid target for small telescopes. (18) Melpomene is located in the constellation of Cetus and is roughly the same brightness as Juno, peaking at magnitude 7.9 on Oct 10 and fading to magnitude 7.9 by month’s end.
Melpomene is another stoney S-type asteroid and similar to Iris was also discovered by John Russel Hind. Found in 1852, it is his 5th of 10 asteroid discoveries.