In The Sky This Month – September 2009
September 1, 2009 63 Comments
This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of September 2009. Jupiter continues its reign as not only king of the planets but king of the evening sky.
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 -2.8, Jupiter is ~13 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 already located high enough in the southest sky by the end of dusk for easy observation. Due to Jupiter’s location in the southern constellation of Capricornus , it never gets very high above the southern horizon this year.
Aug 2 – Nearly Full Moon passes within 3° of Jupiter and Neptune
Aug 29 – Moon within 3° of 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 -2.8 while Neptune will be a faint +7.8. That makes Jupiter over ~17,000 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 at opposition which means it is at its closest to Earth and at its brightest. 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).
Sept 17 - Uranus at opposition
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. At magnitude +0.9, its brightness matches those of many of the brightest stars visible in the morning sky. This month Mars marches through the constellation of Gemini. Mars will continue to brighten as it approaches its opposition on Jan 29 of next year.
Sept 13 – Moon within 1.1° of Mars
Venus - Venus is the brightest “star” in the sky a hour or so before dawn. It was at its highest in the morning sky last month but now begins its slow crawl lower though it will remain an easy object for early risers over the next 2-3 months. For binocular and telescope users, Venus will appear nearly full and is much smaller than it appeared this spring (now 12″ across versus 50″ last spring).
Sept 16 – Moon passes 3° from Venus
Sept 20 – Venus within 0.5° of the 1st mag star Regulus
Mercury - For northern observers, Mercury is not visible until the last days of September when it can be seen as a 1st magnitude star rising in the east just before the Sun.
Sept 20 – Mercury at inferior conjunction (located between the Sun and Earth)
Saturn – Saturn is not visible this month as it is located on the opposite side of the Sun from Earth. As a result, it is located too close to the Sun in the sky to be easily observed. This is a shame because on September 4th, Saturn’s rings will be edge-on and would appear as a very thin line or even disappear in telescopes.
Sept 17 – Saturn at conjunction (located on the side of the Sun opposite Earth)
September does not have many good showers though 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
None this month.
Minor Meteor Showers
Minor showers produce so few meteors that they are hard to notice above the background of regular meteors.
Aurigids (Max Date = Sept 1, Max ZHR = ~3 per hour)
The Aurigids are active from Aug 25 to Sept 8 with a peak on Sept 1. The shower is created by Comet Kiess, a comet only observed in 1911 though it should be back in ~70 years. The Aurigid shower is a minor one with a peak rate of 5 meteors per hour for observers under very dark skies.
This shower does have a history of producing short but spectacular outbursts. Reported outbursts in 1935, 1986 and 1994 allowed scientists to predict an outburst in 2007. The prediction was so good that the peak time was accurate to ~10 minutes. I was lucky enough to have observed this shower that only lasted for ~1 hour. At its maximum it produced a maximum ZHR of ~130 meteors per hour. Unfortunately no outbursts are predicted over the next 25 years, but you never know…
The shower appears to radiate from a position just to the east of the body of the constellation of Auriga. This shower is sometimes called the Alpha Aurigids.
September Perseids (Max Date = Sept 9, Max Rate = ~5 per hour)
The September Perseids are not related to the great Perseids of August. The showers were created by separate comets. This shower showed little sign of unusual activity until enhanced activity was observed on the night of Sept 9, 2008. That surprise display was also the topic of the very first Transient Sky post.
I have not seen any published research into last year’s high activity so its possible this years may see a repeat. Unfortunately, the moon will be bright and will drown out many fainter meteors.
Delta Aurigids (Max Date = Sept 28, Max Rate = ~3 per hour)
This weak shower appears the overlap the Sept Perseids and for some time they were considered part of the same shower. We now know that the showers come from different (though unknown) comets. The Delta Aurigids radiate from a point north of the body of Auriga and the bright star Capella.
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 over 2 years ago on 2006 November 18 by Eric Christensen of the Catalina Sky Survey north of Tucson. At the time the comet was located at 8.7 AU from the Sun which is nearly the distance of Saturn. The comet continues to move closer to the Sun and Earth and is currently 3.8 AU from the Sun and 3.4 AU from the Earth.
The comet is currently around magnitude 8.2 and should be at its brightest this month. It is moving southeast while paralleling the summer Milky Way. This month the comet will cross the constellation of Aquilia. The is well placed for evening observing.
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 from here on out it should remain bright enough to be seen in modest sized backyard telescopes for all of 2009.
All of the above comets are long-period comets which will not return to the inner Solar System for thousands to millions of years. Comet Kopff is a frequent visitor with an orbital period of 6.4 years. Discovered on 1906 August 20 by August Kopff of Germany, the comet has been observed during every subsequent return except one.
The comet reached perihelion at 1.58 AU from the Sun on May 25. Though now moving away from the Sun, the comet still moving closer to Earth and will be located 0.78 AU from us at the end of the month. Recent observations place the comet at magnitude 9.5 to 10.5. It is now slowly fading. The comet spends September in Aquarius.
A finder chart for Comet Kopff can be found at Comet Chasing.
Binocular and Small Telescope Asteroids (V < 9.5)
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 eastward through Pisces. Peak brightness will come at opposition on Sept. 22 when Juno will be as bright as magnitude 7.6. A few degrees to the eats of Juno is another bright asteroid, (18) Melpomene which is described in its own section.
Just a few degrees to the east of (3) Juno lies another nice asteroid target for small telescopes. (18) Melpomene is also located in the constellation of Pisces and is only a little bit fainter than Juno, brightening from magnitude 8.7 to 8.0 in September.
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.