The Transient Sky – Comets, Asteroids, Meteors

I’d like to thank all of you who have visited this page over the past few days. If you have any questions pertaining to comets, asteroids or meteors, please send them to me in the comments section and I’ll try to answer them ASAP. Your comments will also allow me to focus some future posts on topics that people are interested in.

The sky was clear last night although the Moon is a few days from full which is limiting the number of meteors which can be seen. When the Moon is in the sky it makes it hard to see anything faint whether stars or meteors. Even with the Moon, 19 meteors were detected last night. This is close to the my nightly average for September.

Date                     TotalTime      TOT    SPO     ANT     SPE

2008-09-13 UT     9h 13m         19      13        6         0

TOT – total # of meteors detected
SPO – Sporadics (meteors not affiliated with any particular meteor shower)
ANT – Antihelions (meteors coming from the opposition region, opposite the direction of the Sun)
SPE – September Perseids

The best meteor was seen at 10:51 pm. It was slow and bright while leaving a short-lived trail behind it. A movie of the meteor can be seen below. Now that I’ve figured out how to convert avi files to gif, I will be posting more movies rather than just still frames.

Almost a third of last night’s meteors were Antihelions. They appear to come from the part of the sky opposite the Sun and usually do not originate from any one specific comet. Over the millennia many comets have been releasing dust that are visible as meteors when they enter the Earth’s atmosphere. Over time this dust will move away from the orbit of their parent comet. The Antihelions can be thought of as orphan dust particles from 1000s of years worth of short-period comets whose perihelion (closest distance to the Sun) is within the Earth’s orbit (less than 1 AU or Earth-Sun distance). They are inbound particles headed towards their perihelion. Outbound particles are called Helions and since they appear to originate from the part of the sky near the Sun can only be observed during the day. We know of their existence because radio and radar telescopes, which can observe all day and night, have detected them.

Over the past few weeks, their have been an average of ~1 Antihelion observed per night. Last night 6 were observed. Interestingly, four may have come from the same radiant (point of origin on the sky). The plot below shows the path of a number of meteors extrapolated backwards. The circle with an X marks the center of the Antihelion region which covers tens of degrees (about halfway from the center to the right and left edges of the plot). You can see that the backward drawn path of four meteors crosses in the constellation of Pisces just east of the Antihelion point. Could these meteors be related, perhaps originating from a common comet? It’s possible, though with only four meteors in the group it could easily be a chance alignment. Observations from other observers and from other nights are required to confirm if this is a real meteor shower or just statistical noise. IMHO, it’s probably statistical noise.

Plot of meteor paths traced backed to their origin. Plot shows the antihelion region on 2008 Sept. 13 UT.