(meteorobs) NAMN Notes: June 2008

[meteors at comcast.net]

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NAMN Notes: June 2008
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NAMN Notes is a monthly newsletter produced by the North American Meteor
Network and is available both via email and on the NAMN website at
http://www.namnmeteors.org

Contents:

1. June: The Last Slow Month...
2. June Bootids (JBO) the Shower of the Month...
3. (ANT) Antihelion Activity...
4. Other Showers of Interest...
5. Magnitude References...
6. For More Information...


1. June: The Last Slow Month...

June is a good and bad month for meteor observers. The nights are short,
sporadic and antihelion rates are low, and there are no major showers.
As a result, observing hours are rather low. Over the last 4 years,
average January to June Teff is about 180 hours with 1350 meteors. Over
the period July through December, the average is 835 hours and nearly
23,000 meteors.

However, the weather is more pleasant, and skies in the Northern
Hemisphere are usually not as humid as they are later in the summer. Of
course, this year we find our months bisected by the Full Moon near mid
month.


2. June Bootids (JBO) the Shower of the Month...

The only shower (other than the antihelion source) on the IMO working
list this month is the June Bootids. This shower was reinstated on the
list after an unexpected return in 1998. Another occurred in 2004, when
the NAMN recorded 123 in just over 60 hours of observing time during the
month. The total over the three years since is only 19 JBOs in 93 hours
of Teff!

This shower is active from possibly as early as June 20th, and extends
into early July. Currently, the IMO gives the start date as June 22nd,
but video data shows an earlier start of the 20th. The good news this
year is that the activity starts a bit after the full moon, and is above
the horizon all night from the north, so there will be some moon free
hours available to watch. The peak occurs between the 23rd and 27th, so
we should have an opportunity to determine if the shower is going to
give us a treat.

The JBOs, from parent comet 7P/Pons-Winnecke, hit the atmosphere at a
very slow speed, only 18 km/sec, so should distinctively be much slower
than the average meteor. Two other showers, discussed below, also have
speeds as slow, so should also be easy to pick out, once you identify
the radiant.

THE JBO radiant is far away from Arcturus, past the other end of the
kite-like shape of Bootes’ main stars, in the direction of Draco’s tail
and Hercules. Here are the positions at selected dates. You can
interpolate the position for the days in between. There is a large
discrepancy between the reported radiant positions, as well as activity
periods, between the video data and the official IMO positions, so it
would be useful if you can indicate which one seems to be correct. One
way to help with that is to use an alignment cord; a string that you can
stretch out along the meteor path to determine where it intersects the
radiant positions. The IMO 2008 calendar has a graphic of the radiant
position for this year.

The video data suggests a constant RA of 216 degrees (14:24), with a
declination of 34 degrees on the 20th, and 40 degrees on the 24th.

IMO positions:

Start of Activity June 22: RA 222 (14:27), Dec +49
Peak June 27: RA 224 (14:55), Dec +48
End of Activity July 2: RA 226 (15:03), +47


3. (ANT) Antihelion Activity...

In the past, there were a half dozen or more showers identified within
the antihelion area, but the combined rate is no more than a few per
hour. The video data does suggest that to include all the very low
activity radiants for June, the standard 30 (along the ecliptic) by 15
degree (above and below) Antihelion radiant should be expanded a bit to
+/- 10 degrees above and below the ecliptic instead of the normal 15
degree diameter.

So when recording antihelion meteors (avg. velocity 30 km/sec), be a
little generous above and below the ecliptic, which this month passes
between Sagittarius and Ophiuchus, ending up right on Jupiter by the end
of June.

(ANT) Antihelion radiant:

June 1: RA 264 (17:35), Dec -23
June 13: (Before Full Moon) RA 274 (18:18), Dec -23
June 21: (After Full Moon) RA 282 (18:48), Dec -23
June 30: RA 291 (19:24), Dec -21


4. Other Showers of Interest...

In such a slow month of meteor activity, it can pay off to examine other
possible low rate showers. During June, I plot all meteors, since the
low rate allows this without compromising detail during major activity.
The advantage in plotting is that you create a permanent record of what
is observed. For the observers who count meteors only, it is essential
that you accurately determine the radiant location, which is difficult
to do accurately by eye alone. With the aid of an alignment cord, you
have a few seconds to consider whether the meteor path and speed
actually allow assignment to a particular shower. These are showers that
might provide 1 meteor a night, so extra care must be taken to ensure
the assignment of a particular meteor to a shower is correct, otherwise
sporadics might be included. Be sure before you report meteors from
these showers!!

The first is a shower that we will temporarily designate (JPI) June
Piscids. It is between Pisces and Pegasus, and represents the northern
apex radiant. Apex meteors are those that occur in the direction of our
planet’s path through the solar system. We’re plowing through their
paths. A few times a year, the rate rises barely above the background
level, and this is one of those times. Since we are running into these
meteors head on, the velocity is very high, about 61 km/sec. This is
nearly as fast as the Halley meteors (ETA and ORI) and Leonids. This
would be expected to be a very low rate shower, no more than 1 or 2 an hour.

JPI Radiant:
June 21: (after full moon) RA 008 (0:32), Dec +20
June 23: (peak?) RA 009 (0:36), Dec +21
July 11: (End of activity) RA 020 (1:20), Dec +30

(NZC)--Next comes the June Aquilids. Based on video data, and most
visual records, the only active branch is the northern one, which should
be recorded as NZC. (In the past JAQ was used, but NZC defines the
current activity better). These are medium-fast speed meteors (36-40
km/sec). The IAU lists activity from June 9 to July 2; video data
suggests a shorter period from June 22-30. Positions:

NZC Radiant:
June 22: (Start of activity) RA 302 (20:09), Dec -07
June 24: (Peak) RA 304 (20:16), Dec -07
June 30: End of activity RA 309 (20:38), Dec -05

(JLY)/(XDR)
The June Lyrids and Xi-Draconids appear to be the same meteor stream
from two radiants separated by 25 degrees. This year, the peak occurs
right at the full moon, so I would suspect there is little to be
learned. During the last 4 years, the more active position has switched
back and forth. Next year we can investigate these in detail. If you
report these meteors, please be sure on assigning them to one or the
other. The XDRs, reported by Marco Langbroek, and the June Lyrids (from
older AMS data) seem to have a speed comparable to the Lyrids. Most
reports have been from day long outbursts; however the suggested period
of activity is from June 11 to 21, hence coinciding almost perfectly
with the full moon. The peak night (June 15) radiants are:

JLY RA 279 (18:34), Dec +30
XDR RA 280 (18:40), Dec +55

(COR) and (SCU): Corvids and Scutids.

There are two suspected showers of very (extremely) slow angular
velocity. They are far slower than any antihelion meteors and most
sporadics, so should stand out in the unlikely event you get to see one.
I did see two clear Scutids last year (again, plotted records) but have
not yet seen a Corvid. These records consist of a handful of meteors
over the last few decades, so if you are going to report them, please
verify the precise radiant location.

Corvus is the rectangle outlined in LM polygon #23; the radiant is
between that polygon and Spica. The pre atmospheric speed is one of the
lowest possible, about 12 km/ sec. These meteors are best seen before
midnight.

(COR) Corvid Radiant (Peak June 26) RA 192 (12:48), Dec -19.

Scutum is located in the dim stars between Sagittarius, Ophiuchus, and
Aquila. These meteors hit us at about 18 km/sec, again about half the
speed of an antihelion, or the average sporadic meteor. I plotted 2 last
year.

(SCU) Scutid Radiant (Peak June 26) RA 282 (18:48), Dec -03

One other shower I will mention is the tau-Aquarids (TAQ). This is also
a one or two a night shower, with a radiant at RA 340 (22:40), Dec -11.
The peaks in the past have been near June 29, with an impact speed of 65
km/sec, VERY fast.


5. Magnitude References...

The brightest stellar object in the sky is Jupiter, at magnitude -2.6 in
the southern sky.

0 magnitude stars include Vega, nearly overhead, and Arcturus.

+1 Magnitude stars are Altair (in Aquila) Antares (In Scorpio) and Deneb
(the Tail of Cygnus).

+2 Magnitude stars include the brightest in Ophiuchus, and the brightest
two in Cassiopeia.

The 4 stars that make up the diamond of Delphinus are magnitude +3.8,
+3.6, +4.4, and +4.3. The one further to the south is 4th magnitude.

Full Moon is the 20th, so the period from the 18th to 22nd will be
heavily affected by the moon.


6. For More Information...

For radiant positions and more detailed descriptions of showers, see the
IMO 2008 Meteor Shower Calendar at:  http://www.imo.net/calendar/2008.

Feel free to contact us for questions and comments!!
-------------------------------------
NAMN email: namn at namnmeteors.org
NAMN website: http://www.namnmeteors.org

Mark Davis, meteors at comcast.net
Goose Creek, South Carolina, USA
Coordinator, North American Meteor Network

Wayne T Hally, meteoreye at comcast.net
High Bridge NJ
Writer, NAMN Notes

Lew Gramer, dedalus at alum.mit.edu
Homestead, Florida, USA
Coordinator, Public Outreach
Owner/Moderator, 'MeteorObs'

Kevin Kilkenny, namnfireball at earthlink.net
Staten Island, New York, USA
Coordinator, Fireballs and Meteorites

Back issues of NAMN Notes can be found online at the NAMN website and in
the MeteorObs archives at:
http://www.meteorobs.org by selecting 'Browse Archive by Month'

To subscribe to the meteor email list:
Contact Lew Gramer at: dedalus at alum.mit.edu

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Here's to 'Clear Skies' for June...

June 2008 NAMN Notes
Written by Wayne T. Hally & edited by Mark Davis
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