[Prev][Next][Index][Thread]
(meteorobs) Directions for new observers...
Jai, Harry et al...
Several good questions have been asked lately by new observers -
>how do I distinguish between meteors from an active shower and sporadics.
Does it
have something to do with where the meteor seems to originate from in the
sky? ... I would also like to know about "radiant"... Which compass
direction should one face to see the activity tonight ?
Meteors from an active shower could mean a major shower, ie. lots of meteors
per hour, or a minor shower, ie. very few if any meteors per hour. There
are lots of major showers, and minor showers visible with just the naked eye.
If they do belong to a known 'shower', then they appear to all come from a
certain place in the sky, if you traced the 'line' of the meteor back. This
tiny area in the sky is called the 'radiant'.
You could be facing west and see a meteor, and 'trace it back' in the sky to
find out it was an Orionid meteor, for instance. Or, you could be facing
north, or any other direction. In other words, you can see meteors anywhere
in the whole sky on any night.
If you can 'trace them back' and they seem to come from the shower 'radiant'
or origin point, then they are a shower meteor. If they don't seem to come
from there, then they are called 'sporadic' or 'non-shower' meteors.
>Supposing the RA and Dec is specified for some object, how do I locate it in
the sky? (The only equipment I have are my eyes!)
Good question. RA and Dec mean Right Ascension and Declination. These are
basically like latitude and longitude in the sky. We use topographical maps
to pinpoint our location on earth, and RA and Dec are our 'grid lines' for
pinpointing our location in the sky.
The Orionids have a radiant at 095 i.e. RA 06h20m, Dec +16. So what does
this mean if you don't have a sky map?
In the NAMN Notes for October, the next paragraph down from the one you
quoted reads: "At the maximum, the radiant is near the left foot of Gemini,
in the top left part of the constellation of Orion". This description was
included for those people who might not yet have a sky map.
However, it is highly recommended that you get your own 'sky map' so that
you can check out 'radiant' positions, learn your constellations better, and
learn about other neat things too, in the sky, by referring to their RA and Dec.
The maps that I would recommend are both available from Sky Publishing
Corporation. Order numbers: from Canada and the US, call 800-253-0245.
From outside Canada and the US, call +1-617-864-7360 or write to: Sky
Publishing Corporation, P.O. Box 9111, Belmont, MA 02178-9111, USA. Their
website is at http://www.skypub.com and orders can also be placed through
orders@skypub.com
1) Wil Tirion's Bright Star Atlas 2000.0, Sky & Tel order number #96271,
$10.95 US...
... or ...
2) if you want an excellent book combined with your star maps, I would
highly recommend Norton's 2000.0 Star Atlas and Reference Handbook, 19th
edition (new!), Sky & Tel order number #35655, $29.95 US. <This is a good
Christmas gift idea, folks, the new edition has just come out - and the
price for this book has come down! ;>
While you're at, why not order a copy of the book 'Meteors' by Neil Bone,
Sky & Tel order number #46670, $18.95 US...
These atlases both use RA and Dec as the 'grid system' for the sky, and the
maps are nice and easy to use. Personally, I took a pencil to both - and
joined all the constellation star pattern lines! ;> These now show up easily
in the dark. I also took a thin yellow marker, and traced over the dotted
constellation boundary lines, so that they now show up well during the
daytime when I am working with my atlas... but don't bother me at night.
You may have noticed another number in front of the coordinates that were
listed for the Orionid radiant: 095 i.e. RA 06h20m, Dec +16.
The Right Ascension is 6 hours 20 minutes. The Declination is +16 degrees.
Ok, so that's marked on the sky map! The number in front of the RA and Dec
is just another way of specifying RA. The '095' refers to a special degree
measuring method, and is used by the IMO, International Meteor Organization.
It is confusing a bit, as you won't find it marked on your star atlas when
you're looking to see where the radiant is! You can do one of 4 things with
this number:
1) ignore it, and just use RA and Dec, until you get more experienced and
feel you need this number!
2) if a shower's radiant is <only> listed, for example, as 095 +16, for the
Orionids, convert it to RA and Dec by: dividing 095 by 15 to get 6.33, the
6 means RA 6 hours, then taking the .33 times 60 to get 19.8 minutes. The
Dec stays the same, +16 degrees
3) mark this degree system on your star atlas in pencil above the RA and
Dec... RA 0 hours is 0 degrees... RA 1 hour is 15 degrees.... RA 2 hours is
30 degrees... all the way to RA 23 hours is 345 degrees. That way, no
matter how the radiant is listed, you can just read it off your star map!!
4) or, if you just want a table for reference, there is a reference table
that will convert the IMO degree system to RA for you.
Personally, I prefer marking the degree system on my star atlas... I mean,
when you're going out to observe, you need to know where <in the sky> to
look for the radiant, not just in some book or atlas! In other words, you
need to know that the numbers, in this case for the Orionids, refer to a
point near the left foot of Gemini, the constellation of the twins!
Lastly, even once you have an atlas, you still need to know the
constellations! Like, what does Gemini look like? What does Leo look like?
Several books that show what each constellation looks like are:
1) Stars, the Golden Nature Guide, by Zim and Baker, pocketbook
2) The Stargazer's Guide to the Galaxy, by Q.L. Pearce, softcover
Both of these books are currently available in most normal bookstores for
about $5 or $6 US. Sometimes they put them in the adult science section,
sometimes in the children's science section, so check both! These books are
both wonderful for learning the constellations!
Anyway, hope these comments help. Basically, I'd highly recommend getting
yourself a sky map. I know there's a standing North American joke about
'guys not needing maps' to find their way from point A to point B, but when
it comes to the sky.... I would recommend it! ;>>
Clear skies,
- Cathy
===================================================
Cathy Hall, chall@cyberusdot ca
Ottawa, Ontario, Canada
RASC, Royal Astronomical Society of Canada, Kingston Centre
NAMN, North American Meteor Network
===================================================