Perseid Shower
CJ
Thanks to David Entwistle for his post on the ZHR (Zenithal hourly rate). I
thought at the time it was reasonable for me to expect to see at least one
meteor each night between 11 p.m. and midnight, as when the radiant is at 27
degrees the expected ZHR is divided by 2, when it gets to 42.5 degrees the
ZHR is divided by 1.43. When it reaches 52.2 degrees it is divided by 1.25
and finally at an altitude of 65.8 it is divided by 1.11. The expected ZHR
for the maximum is close to 70.
The expected rate for earlier this week was 7 meteors per hour so I
presumed that I would see at least 3 per hour. However when I checked the
figures again they are quoted for a naked eye limit of 6.5 magnitude so
unless you have really clear skies the fainter ones will elude you. My naked
eye limit is 4.5 magnitude when I was viewing, and when the Sun is due north
at this time of the year I can manage to see 5 th magnitude stars. So that
is why I saw none and also I was only watching for 80% of the time in the
relevant area due to standing and not being laid down.
For the evening of August 12 th at 23 00 BST here in Barnsley South
Yorkshire the radiant is 32 degrees high, at midnight BST it is 38 degrees
high. August 13 th 1 a.m. BST the radiant is 44 degrees high, then at 2 a.m.
BST it is 51 degrees high and finally at 3 a.m. it is 59 degrees high. The
Sun is 18 degrees or more from 23 00 hrs BST until 3 a.m. so you should
achieve your naked eye magnitude limit during these 4 hours. All I can say
is that 17 years ago I was in an exceptional clear country side area at this
time and from 1 a.m. to 3 a.m. it was one of the most fantastic sights that
I have seen. I counted over 30 per hour for these 2 hours. I estimated the
limiting naked eye limit at 6 magnitude.
So good weather, clear dark skies and viewing a few nights either side of
August 12 th should pay results. I have also seen that the rates have
decreased from 1995, no doubt due to the fact that the parent comet
Swift-Tuttle passed by the Earth 3 years earlier in 1992 and probably seeded
the orbit, so it may increase again for the next approach in 2122. The thing
I find puzzling about the comet is when it was recovered for its 1992
apparition it was slightly out of its predicted position in the sky. It was
even reported then in the press that in 2122 it could collide with the
Earth. But further checks on its orbit ruled this out.
I cannot find anywhere on the internet figures of its passage to calculate
when it reaches its outer distance from the Sun or being able to calculate
how much it will miss the Earth Moon system by in 2122. The only relevant
data I could find is that is the largest know object with the closest
approach to us. It is estimated that it is nearly 3 times larger that the
object that caused the Dinosaur extinction 65 million years ago. Perhaps
someone who is more diligent than me can find the relevant data. My Starry
night program does not list the ephemeris of it either. Please check any
other programs which you have for details about its inclination etc please
as I am beginning to wonder why I cannot find data on the comet. The comet
is listed as 109P/Swift-Tuttle.
Eddie Lyons
"CJ" <cj...@blueyonder.co.uk> wrote in message
news:KdC7o.75433$Y21.17190@hurricane...
> I cannot find anywhere on the internet figures of its passage to
> calculate when it reaches its outer distance from the Sun or being able to
> calculate how much it will miss the Earth Moon system by in 2122. The only
> relevant data I could find is that is the largest know object with the
> closest approach to us. It is estimated that it is nearly 3 times larger
> that the object that caused the Dinosaur extinction 65 million years ago.
> Perhaps someone who is more diligent than me can find the relevant data.
> My Starry night program does not list the ephemeris of it either. Please
> check any other programs which you have for details about its inclination
> etc please as I am beginning to wonder why I cannot find data on the
> comet. The comet is listed as 109P/Swift-Tuttle.
>
Try the JPL Horizons web site: http://ssd.jpl.nasa.gov/?horizons.
Eddie Lyons
Portsmouth, UK
David Entwistle
<cj...@blueyonder.co.uk> writes
>
> So good weather, clear dark skies and viewing a few nights either side
>of August 12 th should pay results. I have also seen that the rates
>have decreased from 1995, no doubt due to the fact that the parent
>comet Swift-Tuttle passed by the Earth 3 years earlier in 1992 and
>probably seeded the orbit, so it may increase again for the next
>approach in 2122. The thing I find puzzling about the comet is when it
>was recovered for its 1992 apparition it was slightly out of its
>predicted position in the sky. It was even reported then in the press
>that in 2122 it could collide with the Earth. But further checks on its
>orbit ruled this out.
>
>I cannot find anywhere on the internet figures of its passage to
>calculate when it reaches its outer distance from the Sun or being able
>to calculate how much it will miss the Earth Moon system by in 2122.
>The only relevant data I could find is that is the largest know object
>with the closest approach to us. It is estimated that it is nearly 3
>times larger that the object that caused the Dinosaur extinction 65
>million years ago. Perhaps someone who is more diligent than me can
>find the relevant data. My Starry night program does not list the
>ephemeris of it either. Please check any other programs which you have
>for details about its inclination etc please as I am beginning to
>wonder why I cannot find data on the comet. The comet is listed as
>109P/Swift-Tuttle.
>
Hi CJ,
Good work on calculating the viewing prospects for the Perseids.
Eddie has provided an excellent source for the comet's ephemerides.
With respect to the difficulty fitting the orbit of comet Swift-Tuttle
to its observations, that's interesting and not something I'd read
previously.
Gary Kronk's web site and books are always an excellent source of
information regarding these events.
<http://cometography.com/pcomets/109p.html>
The following paper by Yau, Yeomans and Weissman gives a lot of details.
<http://adsabs.harvard.edu/abs/1994MNRAS.266..305Y>
Good luck with the weather for the Perseids - I hope to be out myself.
--
David Entwistle
David Entwistle
<da...@radiometeor.plus.com> writes
As you possibly know, you can download the latest comet data for Starry
Night program here:
http://www.cfa.harvard.edu/iau/Ephemerides/Comets/SoftwareComets.html
However, this data will only generally include comets near perihelion -
the ones which may be observed by modest telescopes. The current list
doesn't include 109P/Swift-Tuttle, which is a long way from perihelion.
--
David Entwistle
CJ
"Eddie Lyons" <eddie...@hotmail.co.uk> wrote in message
news:x4F7o.61777$LU.58859@hurricane...
That was a fantastic help for me as I was beginning to wonder if the
original data that it would collide with the Earth had been covered up. I
know that one of my foibles is that things are covered up by authorities to
stop panic either real or perceived to allay public concern.
I shall try to unravel the data and try to glean more information from the
data.
CJ
"David Entwistle" <da...@radiometeor.plus.com> wrote in message
news:YYm0V0DA...@192.168.0.2...
Sorry I pushed the reply button without writing, thanks for your help. I
think your link will be updated by the update comet/asteroids/satellites
button in the LiveSky dropdown item.
Eddie Lyons
>
> That was a fantastic help for me
You're welcome. 8-)
Eddie Lyons
Portsmouth, UK
Nozza
Saw a very bright meteor fly West to East across the sky - not quite
where I was expecting a Perseid to come from. Brightest meteor I've
ever seen - much brighter than a low Venus it was heading towards. At
first I thought it was a firework.
Noz
pete
the West last night?
I saw a couple of bright ones, too. Though I was out from about 23:30 -
00:30. Very clear, very dark (relatively speaking - probably between
4 and 4.5 at best) and after the rain quite transparent as well.
Nozza
Ooops - thanks for pointing that out Pete!
Noz