Meteor Outbursts: Amateur visual observations are more valuable than ever Mark R' Kidger Instituto d

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Meteor Outbursts Amateur visual observations are
more valuable than everMark R. KidgerInstituto
de Astrofisica de CanariasSpanish Meteor
Societymrk_at_ll.iac.es
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Introduction

• Meteors are small grains of interplanetary debris
  released from comets.
• A zero magnitude meteor has a mass that may be as
  small as 0.07g.

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Introduction

• The velocity of entry in the Earths atmos-phere
  ranges from ?18-71km/s.
• What we see is the ionization wake of the grain
  burning-up at ?100-150km.

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Introduction

• Meteors are divided into two classes shower
  meteors and sporadics.
• Shower meteors come from a well-defined radiant
  point and are usually associated with an active
  comet (e.g. the Orionids and Eta Aquarids with
  Comet Halley).
• They represent material released by the comet in
  the past.

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Introduction

• Around 50-60 meteor showers are known and
  studied, although there may be many more.
• Only a few meteor showers show strong activity
  (gt40 meteors/hr) the Quadrantids Eta Aquarids
  Perseids and Geminids
• Most meteor showers are very weak (lt4 meteors/hr).

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Introduction

• Sporadic meteors cannot be identified with any
  shower.
• They probably represent the remains of extremely
  old showers that are now so dispersed that they
  are unrecognizable.
• Any night of the year one sees around 10 sporadic
  meteors per hour in perfect conditions.

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Why study meteors?

• Meteors sample the historical activity of comets.
• From observing meteor activity we can calculate
  the mass ejected from a comet in the past.
• We can estimate, for example, from observations
  of its meteor showers, that Comet Halley has
  returned around 3500 times in the past.

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Why study meteors?

• Meteors are samples of cometary material.
• By studying meteors we can learn about the mass
  distribution of cometary ejecta.
• We can learn about the physics of the cometary
  nucleus.
• We can learn about the composition of cometary
  dust.

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Why observe meteors?

• Meteor observing requires almost no equipment.
• It is one of the very few fields of astronomical
  observation in which the naked eye observer makes
  the key contribution to study.
• It is principally an amateur field ? The
  amateurs contribution is VITAL.

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Why observe meteors?

• Meteor observing requires dedication.
• A search for clear, dark sites.
• Long hours of observation.
• But...
• Lends itself to group observing.
• It is an enjoyable and productive activity for
  astronomical societies and observing groups.
• Professional studies require a lot of data.

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Meteor outbursts

• Most meteor showers have fairly constant activity
  from year to year, but
• An important fraction of showers are highly
  variable in activity, either
• There is an annual shower, seen every year, but
  there is much higher activity in some years.
• The shower is usually very weak, or undetectable,
  but occasionally shows activity.

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Meteor outbursts

• A meteor outburst is an increase in activity to
  well above its normal level.
• Some meteor outbursts (e.g. the Leonids) can be
  predicted to first order.
• Most meteor outbursts are completely unexpected.
• There are probably several outbursts per year,
  but few of them are observed.

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Meteor outbursts

• The 1990s have been rich in important meteor
  outbursts (100-1000 meteors/hr)
• The Perseids in 1992, 1993, and 1994 (smaller
  outbursts in 1995 - ?).
• The Leonids in 1998 (1999? 2000?)
• The Giacobinids in 1998
• The Alpha Monocerotids in 1995
• The June Draconids in 1998 etc.

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Meteor outbursts

• Almost all observations of these outbursts have
  come from amateur visual observers.
• However, some of the outbursts are seriously
  under-observed due to
• Short duration - extremely difficult to observe.
• Not predicted - few observers witness it.
• Bad weather/timing - lost to bad weather or can
  only be seen where there are few/no observers.

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Alpha Monocerotids 1995

• This outburst lasted only ?40 minutes and the
  main activity ?10 minutes.
• The outburst was well observed from Spain because
  the maximum was predicted.

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June Draconids 1998

• This shower was totally unexpected as it should
  not exist now.
• It was poorly observed because observers were
  taken by surprise.
• The start was very abrupt.

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Giacobinids 1998

• A shower that was predicted, but the time of
  maximum was very uncertain.
• Some Japanese reports suggest that the activity
  briefly touched storm level.

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Leonids 1998

• Spectacular activity, but at a much lower level
  than first reported.
• Widely observed despite coming one night early.
• Does not imply a Leonid storm in 1999.

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Leonids 1999

• The main maximum (?250/hr) came from material
  released in the 14th Century.
• Only a small peak (?80/hr) was seen at the
  expected time.
• Favourable for Europe in 1999, but ...