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(meteorobs) NAMN Notes: April 2000
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NAMN Notes: April 2000
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Introduction:
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://web.infoavedot net/~meteorobs
Contents:
1. Spring Brings the Lyrids...
2. Other April Showers...
3. NAMN Member Discovers Comet!...
4. Constellation Review - Leo...
5. Recent Observations, March 2000...
6. Upcoming Meetings...
7. For more info...
1. Spring Brings the Lyrids...
With the first hint of spring, and the flowers starting to appear, we have
the Lyrid meteor shower to wake us up from winter hibernation! Actually,
April 1st shows no flowers yet for the Canadian co-author, and who could yet
get snow. However, it is nice to be getting some warmer nights that are
actually above a freezing temperature.
The Lyrids (LYR) are the first major shower of the year for the majority of
observers. This year, the maximum, the date of highest rates, is on April
21st, with the peak expected between 22h UT on the 21st and 05h UT on the
22nd. Some activity from this shower can be seen from about April 16th to
25th, but the rates will be much lower away from the peak.
The ZHR, zenithal hourly rate, at maximum, is about 15 meteors per hour with
the unaided eye under a dark sky. This is only true if the radiant, or the
area in the sky where the meteors seem to come from, is directly overhead.
However, this year full moon is on April 18th, so the observed rates will be
lower. The Lyrids are still worth watching though, as rates have sometimes
been variable, and much higher. In 1982, for a brief period, the number of
meteors climbed to about 90 per hour. Back in 1803, an observer counted 167
meteors in about 15 minutes, then lost count. The bottom line is that if you
don't go out to look, you'll never know what you missed!
These meteors are medium velocity, at about 49 km per second. The radiant
on April 21st is at 271 degrees, ie. RA 18h 04m, Dec +34, which is about
halfway between theta and nu Hercules, and not actually in the constellation
of Lyra at all. According to Kronk, the average magnitude, the brightness
of the meteors, is about 2.4, which is just a bit fainter than the main
stars in the Big Dipper.
The Lyrids are believed to be old debris from Comet Thatcher found back on
April 5th, 1861 by A.E. Thatcher of New York. The comet has an elliptical
orbit and visits us about every 415 years. The meteors are visible every
year - and in fact, the Lyrid meteor shower is the oldest shower to be
mentioned in ancient records. Those records date back to 687 B.C., long
before the actual source of the shower was discovered.
2. Other April Showers...
The ecliptic meteor activity this month, until about April 15th, continues
to be the Virginids (VIR) which started in late January. The ZHR rate is
about 5 meteors per hour. These are just barely medium velocity meteors,
at about 30 km per second. At the end of March, the radiant was at 198
degrees, ie. RA 13h 12m, Dec -05, near the star theta Virgo. By April 15th,
it will have moved to 205 degrees, ie. RA 13h 40m, Dec -08, which is about 5
degrees up to the left of Spica.
Starting about April 15th, the Sagittarids (SAG) become the ecliptic
activity. These continue to have the same velocity, about 30 km per second,
and a ZHR rate of about 5 meteors per hour. On April 15th, the radiant will
be at 224 degrees, ie. RA 14h 56m, Dec -17, which is about 2 degrees left of
alpha Libra, the star called Zubenelgenubi. By April 30th, the radiant will
have moved to 233 degrees, ie. RA 15h 32m, Dec -19, which is about 4 degrees
south of gamma Libra. Note that in April, the radiant is not in
Sagittarius, but in Libra, in spite of its name. This shower has been
associated with fireballs, even in old historical records dating back to 354
A.D. Many amateur observers (including the Canadian co-author) grew up
being told that April was "Fireball Month".
Also starting about mid-month, we can begin to see the Pi Puppid (PPU)
meteor shower. It reaches a maximum on April 23rd, just past the Lyrid
peak, but shower members can be seen until the end of the month. The
radiant at maximum is at 110 degrees, ie. RA 07h 20m, Dec -45, which is
about 15 degrees below eta, the left foot of Canis Major, very low for us in
the northern hemisphere. The ZHR rate is listed as variable, although rates
did reach about 75 meteors per hour in 1977 as observed from Australia.
These
meteors are very slow, with a velocity of about 18 km per second. This is a
fairly young meteor shower, only noticed since about 1972. The source of
the meteors is Comet 26P/Grigg-Skjellerup, which visits us about every 5
years.
Lastly, the final shower of note this month is the eta Aquarids (ETA) which
will reach a maximum on May 5th and will start to appear as early as April
19th. On April 25th, near last quarter moon, the radiant will be at 328
degrees, ie. RA 21h 52m, Dec -05, which is about 5 degrees left of beta
Aquarius, the star Sadalsuud. On April 30th, closer to new moon, the
radiant will be at 332 degrees, ie. RA 22h 08m, Dec -04, which is about 4
degrees south of alpha Aquarius, the star Sadalmelik. By May 5th, at
maximum, ZHR rates will reach about 60 meteors per hour. Rates in April
will be lower, leading up to that. These are fast meteors, with a velocity
of about 66 km per second. This shower represents debris from Halley's
Comet, so is particularly appealing to watch!
For help in judging the magnitudes of brighter meteors seen in April, the
brightness of the planets visible are as follows, rounded to the half
magnitude:
Venus -4.0 (in southern hemisphere only)
Jupiter -2.0
Saturn 0.5
Mars 1.5
On April 6th, just past new moon on the 4th, make sure you take a look at
the moon and planets in your western sky just after sunset. Mars will be 5
degrees north of the moon, Jupiter 4 degrees north of the moon, and Saturn 3
degrees north of the moon. At the end of the month, on April 27th, Uranus
will be 1.3 degrees north of the moon, but at magnitude 5.8 won't be too
visible unless you have a nice dark sky.
Lastly, don't forget - if you need some handy star charts to mark this
month's meteor radiants on for use in the field, go to our NAMN website and
print yourself off a set! You might want to explore some of the other
resources on the site as well, such as the NAMN Observing Guide, which
answers many questions for beginners. Check us out at:
http://web.infoavedot net/~meteorobs
3. NAMN Member Discovers Comet!...
NAMN member Michael Boschat, of Halifax, Nova Scotia, Canada has recently
co-discovered a comet by searching images obtained with the SOHO satellite.
Comet C/2000 E1 (SOHO) was discovered on March 4, 2000 by M. Boschat, M.
Meyer, T. Harincar and M. Oates. Several of the SOHO images can be seen at
http://www.atm.daldot ca/~andromed/
Congratulations Michael!
4. Constellation Review - Leo...
Last month, we took a look at the constellation Ursa Major and its use for
meteor observers. This month, we travel further down, below the Great Bear,
and examine the constellation of Leo Major, probably the most prominent star
pattern of spring.
Leo is the Lion and has been patterned as such since ancient times in
Egypt and many other countries. Its main feature is a large backwards
"question mark" in the sky, which marks the head of the Lion and is the
source of the famous Leonid meteor shower in November. At the base of the
question mark is the bright star Regulus, regarded by the Persians as one of
the four guardian stars of Heaven - the others being Fomalhaut, Aldebaran
and
Antares. It is sometimes called Cor Leonis, the "Lion's Heart". The actual
name Regulus was coined by the astronomer Copernicus.
At the back end of Leo is a triangle pattern with the bright star Denebola,
called the "Lion's Tail" at the eastern point. This star is also known as
Serpha, from the Arabic Al Sarfah, meaning the "Governer of the Weather".
In ancient Egypt Leo was always associated with the Sun, as the annual
flooding of the Nile River occurred when the Sun entered the constellation
of Leo.
So, what can Leo teach us for meteor observing?
If unsure of your direction, remember that the Lion's head is facing west.
You will remember, of course, that the pointers of the Big Dipper point to
the north star, but sometimes it is useful to have a sense of what is west,
and what is east in the sky as well.
The star Regulus at the base of the sickle, is used as a standard magnitude
1.5 star for estimating meteor magnitudes. Denebola, at the tip of the
triangle at the rear of Leo, is used as a standard magnitude 2.0 star, and
is of course fainter than Regulus. The larger the number, the fainter the
star - and meteor.
Up at the top of the question mark we have 3 stars that are useful for
judging fainter meteors. These stars are mu Leonis, epsilon Leonis and
lambda Leonis, better known as Rasalas, Ras Elased Australis and Alterf.
Moving from the top of the Lion's head to his mouth, Rasalas is a standard
4.0, Ras Elased a standard 3.0, and Alterf at his mouth is a standard 4.5.
These stars are all shown and labeled on the star charts at the NAMN
website. Leo is on chart 2. The website is at
http://web.infoavedot net/~meteorobs. All four star charts are easily
printed, just set your printer setup to "landscape" mode first.
For estimating your "limiting magnitude" or the faintest star that your
particular eyes can detect under your particular sky conditions, you can use
Leo as well. The IMO, International Meteor Organization, has designated an
area in Leo as one of its standard areas for measuring LM, limiting
magnitude. Take the following 4 stars:
1. Regulus, the bright star at the base of the sickle
2. Algeiba, 2 stars up the sickle from Regulus
3. Denebola, at the tip of the triangle at Leo's rear
4. Zosma, at the top of that rear triangle
Count the number of stars that you can see in the four-sided area bordered
by these stars. Count these 4 border stars as well. Then, using the IMO
table for this area, called area 9, see what your LM is. Part of this table
is as follows:
#stars LM
7 4.4
8 5.0
11 5.6
13 5.7
15 6.0
18 6.1
20 6.3
For example, if you counted 11 stars, your limiting magnitude is 5.6.
If you counted 19, your LM is 6.2. Sometimes you have to calculate a bit
if you're in a gap, like between 8 and 11 stars.
The IMO table for area 9 in Leo goes all the way down to 45 stars with a
faintest star of 7.5, but unless you're under a pitch black sky on some
mountain peak in the wilderness, you're never going to have to count that
high! You'd also probably lose count far before then. In fact, if you ever
have a sky that good, you're probably better off using an area with fewer
stars to count. For instance, there is a triangle in Virgo, called area 10,
where you can rate a 7.5 sky by only counting 31 stars - a lot better than
trying to count 45!
For the skies that most of us will encounter, the IMO limiting magnitude
triangles or 4-sided areas require us to count maybe up to a dozen stars or
so, which isn't too hard to do. In Leo, 15 stars means a 6.0 sky, which is
a nice dark sky for most of us. Over the course of the night though, the
faintest star you can see may change a bit - so do a star count every half
hour. But don't bother figuring out your limiting magnitude while you're
observing. Just do the actual count of stars and figure out the
limiting magnitude when you write up your meteor report at home. Most
observers also try to count a couple different designated areas - we are
just giving information on area 9 in Leo for this month's article. More
info can be found on the IMO website at www.imodot net - and you can print
yourself off details of the various LM areas and their related count tables.
So, watching the constellation of Leo this spring can teach you some more
about meteor observing - how to estimate the magnitude of both bright and
faint meteors, how to determine how good your eyes are and how dark your
skies are, and lastly, some more concepts of direction in the sky.
5. Recent Observations, March 2000...
In a month when the most active meteor shower is the Virginids, it is
probably inevitable that the greatest activity would be produced by sporadic
meteors. This year maybe even more so as several observers noted and
commented on what they thought were unusually high sporadic rates. Jure
Atanackov, Mike Linnolt, Robert Lunsford and Kim Youmans all reported what
could be considered higher than normal activity (10+ per hour) for this time
of the year. In all, during 13 nights of observations, 6 observers reported
279 sporadic meteors over a little more than 40 hours of observing. The 2
Camelopardalids, 7 Delta Leonids, 5 Gamma Normids and 45 Virginids reported
during this same time period paled in comparison to the sporadics.
At the beginning of the month, Malcolm Curry, IMO Telescopic Commission
Director, alerted us to the possibility of Kappa Leonid meteors being
visible in early March. Mike Linnolt, from Hawaii on March 5, was the only
observer to report any when he recorded 2 possible candidates, although both
were a little south of the listed radiant.
For a complete listing of March observations, visit the home page of NAMN at
http://web.infoavedot net/~meteorobs. I would like to thank the following
observers who sent in observations during the month of March:
Jure Atanackov Mike Linnolt
John Drummond Robert Lunsford
Javor Kac Kim Youmans
6. Upcoming Meetings...
April 10-14, 2000 - Britain:
IAU Colloquium 181 on 'Dust in the Solar System and Other Planetary Systems'
will be held at the University of Kent at Canterbury, in the United Kingdom.
This colloquium is the 7th in a series dedicated to studies of
interplanetary dust. Areas to be covered will include such topics as
cometary dust modeling, asteroidal sources of meteoroids, observations of
interplanetary dust from both earth and space, and instrumentation for dust
collection and analysis. Publication of the proceedings is planned after
the meeting. Details are available on the website at:
http://wwwdot ukc.acdot uk/physical-sciences/space/
April 16-19, 2000 - Israel:
The Leonid MAC Workshop 2000 will be held in Tel Aviv, Israel. The workshop
focuses on studies of the Leonid shower, and will present the first results
of the Leonid MAC campaign and ground based program, as well as discuss
future efforts and opportunities for observing campaigns from 2000 to 2002.
The workshop aims to bring recent Leonid storm studies into focus and will
discuss recent progress made in understanding the satellite impact hazard,
the origin of life, new meteor, meteor train and meteor shower models,
sprites, impacts on the Moon, comet composition and ejection dynamics, the
spectroscopy of meteors and meteor trains, laboratory studies that help
explain the observed spectral features, remote sensing - new techniques that
may be deployed during future storms, and many other topics that relate
directly to the exploration of the Leonid showers. More information can be
found at http://leonid.arc.nasadot gov/workshops.
April 16-20, 2000 - Germany:
The conference AMICO 2000, 'Asteroids, Meteorites, Impacts and Their
Consequences' will be held in Nordlingen, Germany. This is a combined
meeting of the Astronomical Society and the German Geological Society, and
is hosted jointly by the Rieskrater Museum Nordlingen and the city of
Nordlingen. A field trip to the Ries and Steinheimer Becken impact craters
is planned. For information, contact Michael Schieber at the Rieskrater
Museum at rieskratermuseum.noerdlingen@donau-riesdot de
July 9-12, 2000 - Austria:
The international conference 'Catastrophic Events and Mass Extinctions:
Impacts and Beyond' will be held at the University of Vienna in Austria.
This is the 4th in a series of meetings on mass extinctions and global
catastrophes, the previous meetings being 1981 and 1988 in Utah, and 1994 in
Houston, Texas. Expected topics include impact events in earth history,
boundary events in geologic time, environmental consequences of impacts,
interpretation of stratigraphic records, and extraterrestrial influences
such as asteroids and comets. More information on the conference can be
found at:
http://www.lpi.usradot edu/meetings/impact2000/impact2000.2nd.html
July 25-August 4, 2000 - Slovenia:
An International Astronomical Camp, IAC 2000, will be held in the Pohorje
Mountains at Mariborska koca (MBK), Slovenia. Work will be divided into
various groups - Solar System, Meteors, Deep Sky, Variables and double
stars, and Astrophotography. For more information, contact Jure Zakrajsek
by email at elizabeta.zakrajsek@guest.arnesdot si
September 11-15, 2000 - Crimea:
The international conference 'Space Protection of the Earth - 2000' will be
held in Evpatoriya in the Crimea. This is the 3rd in a series of
international conferences on the protection of the Earth from the threat of
its collision with asteroids and comets, with the prior meetings being held
in Saint Petersburg and Snezhinsk, Russia.
Topics will cover characteristics of asteroids and comets, their risk,
detection technologies, man-made means of influencing dangerous celestial
bodies, planetary defense, international cooperation, prospects for
utilizing asteroid and comet resources, and other issues. For more
information, contact the SPE-2000 Program Committee by email at:
spe@asteroids.ru
September 21-24, 2000 - Romania:
The IMC, International Meteor Conference, of the IMO, the International
Meteor Organization, is being held in Pucioasa, Romania, about 100 km
northwest of Bucharest. It is being organized by the Romanian Society for
Meteors and Astronomy (SARM), in cooperation with the mayoralty of Pucioasa.
Pucioasa can be reached by direct trains and buses from Bucharest, and a
shuttle bus from the Bucharest airport to the conference site is planned.
Accommodation will be provided in double rooms, and meals served at the
restaurant of the hotel close to the conference site. The conference fee
will be 170 DEM. A deposit of at least 100 DEM is requested for those
interested in attending, and a registration form is on the IMO website at
www.imodot net.
7. For more info...
Contact:
Mark Davis, MeteorObs@charlestondot net
Goose Creek, South Carolina, USA
Coordinator, North American Meteor Network
And check out:
NAMN home page:
http://web.infoavedot net/~meteorobs
Back issues of NAMN Notes can be found on-line at the NAMN website, and in
the meteorobs archives at:
http://www.tiacdot net/users/lewkaren/meteorobs
by selecting 'Browse Archive by Month'
To subscribe to the meteor email list or
To find out information on our weekly chat sessions:
Contact Lew Gramer at:
owner-meteorobs@jovian.com
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Here's to 'Clear Skies' for April...
April 2000 NAMN Notes co-written
by Mark Davis and Cathy Hall
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