Astronomy a Go Go! September Sky Tour
This tool displays the approximate Moon phases for a
given month(images are close approximations). For official phase times and dates
for this month and past months are available from the U.S. Naval
Observatory.
Astronomical Online
Glossary
Download this month's sky map!
Skymaps.com is our favorite monthly
skymap provider. Download either the Northern hemisphere, Equatorial, or
Southern Hemisphere sky map so you can follow along with our viewing
sessions.
Creator: Kym Thalassoudis
Southern Hemisphere Additional Information
As Astronomy a Go Go! finds
its home in the higher Northern latitudes those of you who live south of the
equator will benefit from these two Southern Hemisphere sites: Royal
Astronomical Society of New Zealand's Southern Hemisphere Calendar RASNZ site (absolutely
outstanding) and
Southern Sky Watch.
Great Astronomy Activities!
Citizen Sky
For those in Northern Hemisphere, Capella, the "She Goat" in Aurigae, is
circumpolar. At my 47 deg North, Capella disappears behind the tree line, and
into the light polluted horizon, but she pops up in a few hours and is easy to
find. Also easy to find are epsilon Aurigae (al Maaz the Billy Goat) and "The
Kids" which make a small, long, triangle of stars just to the Southwest of
Capella.
For the next 21 months Epsilon Aurigae, usually the brightest of the trio,
will start behaving quite differently than it has for the past 27 years. Epsilon
Aurigae is a type of variable star called an eclipsing binary. Epsilon Aurigae
and some unknown dark partner, rotate around a common center of mass and every
27 years that dark companion eclipses the giant F-type star. August marks the
anticipated beginning for that eclipse which will last for 714 days, dimming
from 3.0 mag to about half of its brightness.
So why am I calling this a great astronomy activity? Epsilon Aurigae has some
definite quirks and more eyes are needed to help scientist figure out what
Epsilon Aurigae's invisible partner really is! We need help...WE NEED YOU!!
Anyone can participate; we need people to observe epsilon Aurigae, folks to look
at the data for quirks, patterns, or voids, artist to help present the data to
the public, friends willing to get the word out to others! To find out more
visit:
NASA's MicroObservatories
Another fantastic project, that AAGG is supporting all through the month of
September, it the "Capture the Colorful Cosmos" project using the NASA
MicroObservatories. This project gives you the opportunity to direct a robotic
telescope and then manipulate the resulting images!
I had the opportunity to help school age kids, and some kid-like adults,
through the project at the Tacoma Astronomical Society's annual Astronomy Fair
in August and we had a wonderful time! They were using filter, shifting and
stacking images, and turning out images like the pros!
Sweet and innocent "A", and the postcard of M51
he created (Blasters of Death -- go figure), and his sister's Orion composite
image (ahhhhhh!)
LCROSS Impact
Astronomers, amateur and professional a like, who
have access to dark skies and large aperture scopes are encouraged to
participate in imaging and video taping the impact of the Centaur impactor and
the LCROSS satellite with the Moon. The primary objective of the Lunar Crater
Observation and Sensing Satellite (LCROSS) is to confirm the presence or absence
of water ice in the Moon's polar region. But the amazing bit will be the five
body choreography between the Moon, the Centaur rocket/impactor, the Shepherding
craft/research vessel/impactor, and LRO (who was launched with LCROSS) who will
also observe the action, and YOU, on Earth!
I mean... what other impactor mission has its own music
video!
More information can be found at the LCROSS Citizen Observing
Campaign Site.
Images courtesy of: New Mexico State
Univ
Planets for September 2009
September Morning
Planets
(click images to enlarge)
Beginning of the month
End of the month
- Mercury- Starts September headed for the Sun in the early evening
sky, best observed by lower and southern latitudes. By the end of the month
Mercury will join Venus, Mars, and Saturn in the morning sky. 0.5 mag (1st) to
5.5 mag (21st)
- Venus- Beautiful in the morning sky and is heading eastward towards
Regulus. Venus will be half a degree north of Regulus on the 20th of the month
as she heads back towards the Sun. She will pair up with Mercury and Saturn in
the early October sky so make sure you spend some time pre-sunrise time around
the 5th of October with Venus and Saturn making a Mercury breakfast sandwich!
-3.8 mag (1st) to -3.8 mag (21st)
- Mars- Spends the month in Gemini so you'll need to get up early for
this one too! 1.00 (1st) to 0.9 mag (21st)
- Jupiter- AAGG missed Jupiter's vanishing moons due to bad weather but
John Chumack, of The Chumack Observatories, captured the event and has a movie
posted at his site! -2.8 mag (1st) to -2.7 mag (21st)
- Saturn- In conjunction with the Sun on the 17th, moving into the
morning sky. Look for the return of Saturn in October. 1.1 mag (1st) to 1.1 mag
(21st)
- Uranus- At opposition in Pisces on the 17th. 5.7 mag (1st) to 5.7 mag
(21st)
- Neptune- In Capricorn 7.8 mag (1st) to 7.8 mag (21st)
- Ceresand Eta - Finder chart
from the New Zealand RAS (RASNZ) great charts! Northern Hemisphere observers
this time you get to flip the chart or stand on your head!
Vesta chart
temporarily missing...use this
one until site is corrected
Key Dates for September 2009
Days and Times in UT: (help with
time)
Observations are for 10 pm for Northern Hemisphere and 8pm for the
Southern Hemisphere.
Today's sunrise
and sunset times or plan ahead using the US Naval Observatory
Website
Occultation information can be found at the IOTA website!
Astronomical Highlights - September 2009
| 1 |
- Venus 1.2 deg SSW of Beehive cluster (M44) early morning sky |
| 2 |
- Moon near Jupiter in the evening sky |
| 2-3 |
- Jupiter's moons line up in front of and behind Jupiter such that Jupiter
has no moons. See www.spaceweather.com for more details |
| 4 |
- Full Moon 16:03 UT |
|
- Saturn's rings edge on as seen from Earth |
| 6 |
- Mercury stationary beginning retrograde motion |
| 9 |
- September Perseids |
| 10 |
- Moon near Pleiades in the morning sky |
| 9-16 |
- Astronomy A Go Go! at the Afterschool Universe training, the AANC Annual
Meeting, and the ASP conference in San Francisco! |
| 12 |
- Last Quarter Moon |
| 13 |
- Moon very near Mars in the morning sky possible occultation check the IOTA website for
more information |
| 15 |
- Moon near Beehive cluster (m44) in the morning sky |
| 16 |
- Moon at perigee (closest to Earth) 364,053km) |
|
- Zodiacal Lights vis in N latitudes before sunrise in the East next two
weeks (example image, the
reflection of sunlight off interplanetary dust in the plane of the
ecliptic) |
| 17 |
- Moon near Regulus |
|
- Saturn in conjunction with the Sun moving into the morning sky |
|
- Uranus at opposition |
| 18 |
- New Moon at 18:44 UT |
| 20 |
- Mercury at inferior conjunction with the Sun as it moves into the morning
sky |
|
- Venus 1/2 degree NNE from Regulus |
|
- Moon near Spica |
| 22 |
- September equinox 21:22 UT Point in the year where the Sun passes along
the ecliptic into the Southern Hemisphere |
| 24 |
- Moon near Antares in the evening sky possible occultation check the IOTA website for
more information |
| 26 |
- First Quarter Moon |
| 28 |
- Moon at apogee (furtherest from the Earth) 404,432 |
| 29 |
- Moon near Jupiter in the evening sky |
|
October |
| 4 |
- Full Moon |
| 16 |
- In the pre-dawn sky; Arcturus is to the north, the crescent Moon to the
south, and stacked in between, from the horizon, Mercury, Venus, and
Saturn. |
Date information courtesy of: RASC Observer's Handbook, Skymaps.com,
Astronomical Calendar 2009, CalSky, Skymaps.com. sunrise and sunset times
for your home*
Comparative lengths of
day and night
This month our monthly Messier hits some big easy targets, eight more
globular clusters, all are possible in binoculars, and two of these are the
finest globulars which can be seen from northern locations.
Sagittarius is the home of many globular clusters which surround the center
of the Milky Way Galaxy. Seven of the these globulars appear in the Messier
catalog, we will be visiting five of them this month. When you complete the
search for these objects be sure to spend some time scanning this region with
binoculars or a telescope and see what other sights you can discover. I
guarantee you will not be disappointed.
- M13 - The great
globular cluster in Hercules is bright enough to be seen with naked eye and
typically the first GC found by amateur astronomers in the NH. Binoculars easily
show this cluster as a bright fuzzy ball. M13 is partially resolvable in small
aperture telescopes and becomes a fantastic swarm of tightly packed individual
stars through large scopes.
- M92 - Another
globular cluster in Hercules, M92 is easy to find in binoculars appearing
slightly dimmer and smaller than M13. As with M13 it is partially resolvable in
small scopes and is a fine sight in large instruments.
- M14 - A small,
bright globular cluster in Ophiuchus. It is a difficult binocular object, look
for a small fuzzy patch of light. Through a telescope M14 is an even patch of
light, the stars not resolvable except through large scopes.
- M22 - This is
the other great globular in our tour this month. Located just above the teapot
asterism in Sagittarius, M22 can be seen with no optical aid. M22 is easy to
find in binoculars, and easy to resolve in telescopes, with about the same
impressiveness as M13.
- M28 - Located
near M22 in Sagittarius, this is a small bright globular. A tough binocular
object, look for a small fuzzy patch. Easily seen in a telescope, but requires
large aperture to resolve individual stars.
- M69, M70, M54 All of these are small
bright globular clusters laying along the bottom of the teapot in Sagittarius.
Very similar in appearance to M28, these are all tough binocular objects
requiring dark skies and possibly averted vision to see. M54 is slightly
brighter and appears more star like through binoculars than the other globulars.
These are all easily seen in telescopes, though not easily resolvable.
From the Astronomical
Connection and the Moncton Center in Canada
From the Tony
Cecce, Corning, NY - Twelve Month Tour of The Messier Catalog
Comets for September 2009
More comet
information at
Seiichi
Yoshida's comet website. Also checkout Gary Kronk's
comet and meteor pages
Skyhound Comet pages
Historical and Current Events
...Did you know?
Mark has developed his own website
so let's all trot on over and see the pages of wonderful history he has for us
this month!
Help us out by leaving a donation in the ol' PayPal hat
or write us a
favorable review in iTunes of Podcast Pickle or iPodder!
Music Scottish Guitar
Quartet -"Romance Within You"
Black
Lab- "See the Sun"
Anne
Farnsworth- "Saturday Morning"
Earth's major motions for 2009
| Perihelion |
|
Jan 4 15(UT) |
| First Cross Quarter Day |
|
Feb 2-6 |
| Equinox |
|
Mar 20 11:44(UT) |
| Second Cross Quarter Day |
|
May 4-7 |
| Solstice |
|
June 21 05:45(UT) |
| Aphelion |
|
July 4 02h (UT) |
| Third Cross Quarter Day |
|
Aug 5-8 |
| Equinox |
|
Sept 22 21:18(UT) |
| Fourth Cross Quarter Day |
|
Nov 5-8 |
| Solstice |
|
Dec 21 17:47(UT) |
Planet Positions for 2009
| 2009 |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
| Venus |
Sgr |
Cap |
Aqr |
Psc |
Tau |
Gem |
Cnc |
Vir |
Vir |
Sco |
Sgr |
Cap |
| Mars |
Sgr |
Cap |
Aqr |
Psc |
Psc |
Ari |
Tau |
Tau |
Gem |
Cnc |
Cnc |
Leo |
| Jupiter |
Cap |
Cap |
Cap |
Cap |
Cap |
Cap |
Cap |
Cap |
Cap |
Cap |
Cap |
Cap |
| Saturn |
Leo |
Leo |
Leo |
Leo |
Leo |
Leo |
Leo |
Leo |
Vir |
Vir |
Vir |
Vir |
Interesting Planet Pairing for 2009
- December 31, 2008 - Jupiter and Mercury - After sunset a
little more than one degree apart in Sagittarius. Pull out the binos and
telescopes because Mercury will be a mere 15 arcminutes from the globular
cluster M75. All three will be together in one field of view in most home
binoculars.
- January 22nd - Venus and Uranus - After sunset 1.3 degrees
apart a few days later on the 29th they are joined by a waxing crescent moon.
- February 23rd - Jupiter, Mars and Mercury - In the early
morning sky just before sunrise the trio are in a space about 2 degrees wide.
Binoculars will be helpful but beware the quickly rising Sun. The Moon, almost
invisible, will be between Mars and the Sun.
- March 23rd - Mars, Moon, Neptune, and Jupiter - Makes a nice
line-up in the morning sky with Neptune just off the tip of the waning crescent
moon.
- April 21st - Venus, Mars, Uranus, waning crescent Moon, Neptune
and Jupiter - all in the pre-dawn sky together. First the right triangle of
Venus, Mars, and Uranus followed by the waning crescent Moon and then finally by
Neptune and Jupiter. Mars will be a faint 1.41 mag so binoculars will be
helpful. The next day, possible occultation of Venus by the Moon. Check the IOTA
website for occultations in your area.
- May 25th - Jupiter and Neptune - Jupiter is less than 1/2
degree South of Neptune in the morning sky. If you have ever had problems
finding Neptune this would be a good time to try, between now and June.
- June 19th - Venus and Mars - In the pre-dawn sky just south of
a waning crescent Moon. Closer to the Sun is Mercury and the Pleiades.
- August 17th - Saturn and Mercury - Very close to the Sun low
in the evening sky. Much better view for Southern viewers.
- September 3rd UT 4:43 - Jupiter hides its Galilean moons. Not
until 2019 will all of Jupiter's Galilean moons orbit in such a way.
- September 4th - Saturn - Not exactly a pairing but the Earth
will cross the plane of the rings from south to north making the rings invisible
- October 16th - Mercury, Venus, and Saturn - All lined up in
the pre-dawn sky close to the horizon. A faint waning crescent is just south of
the trio.
- December 24th - Jupiter and Neptune - Just after sunset
Jupiter and Neptune sit side-by-side just north of delta Capricornus and east of
the "42,44,45 Cap Wall"
Phases of the Moon 2009
(click to enlarge)
Universal Time
NEW MOON FIRST QUARTER FULL MOON LAST QUARTER
d h m d h m d h m d h m
JAN. 4 11 56 JAN. 11 3 27 JAN. 18 2 46
JAN. 26 7 55 FEB. 2 23 13 FEB. 9 14 49 FEB. 16 21 37
FEB. 25 1 35 MAR. 4 7 46 MAR. 11 2 38 MAR. 18 17 47
MAR. 26 16 06 APR. 2 14 34 APR. 9 14 56 APR. 17 13 36
APR. 25 3 23 MAY 1 20 44 MAY 9 4 01 MAY 17 7 26
MAY 24 12 11 MAY 31 3 22 JUNE 7 18 12 JUNE 15 22 15
JUNE 22 19 35 JUNE 29 11 28 JULY 7 9 21 JULY 15 9 53
JULY 22 2 35 JULY 28 22 00 AUG. 6 0 55 AUG. 13 18 55
AUG. 20 10 02 AUG. 27 11 42 SEPT. 4 16 03 SEPT. 12 2 16
SEPT. 18 18 44 SEPT. 26 4 50 OCT. 4 6 10 OCT. 11 8 56
OCT. 18 5 33 OCT. 26 0 42 NOV. 2 19 14 NOV. 9 15 56
NOV. 16 19 14 NOV. 24 21 39 DEC. 2 7 30 DEC. 9 0 13
DEC. 16 12 02 DEC. 24 17 36 DEC. 31 19 13
Eclipses for 2009
January 26 - Annular Solar Eclipse ( see map,
times, and animation!): The first
solar eclipse of 2009 occurs at the Moon's ascending node in western
Capricornus. An annular eclipse will be visible from a wide track that traverses
the Indian Ocean and western Indonesia. A partial eclipse will be seen within
the much larger path of the Moon's penumbral shadow, which includes the southern
third of Africa, Madagascar, Australia except Tasmania, southeast India,
Southeast Asia and Indonesia.
February 09 - Penumbral Lunar Eclipse ( see map,
times): The first lunar eclipse of 2009 is one of four such events during
the year. The first three eclipses are penumbral while the last (on Dec. 31) is
partial. The Feb 09 event is the deepest penumbral eclipse of the year with a
penumbral magnitude of 0.899. It will be easily visible to the naked eye as a
dusky shading in the northern half of the Moon. The times of the major phases
are listed below.
July 07 - Penumbral Lunar Eclipse ( see map,
times.): July's penumbral eclipse is only of academic interest since the
magnitude is just 0.156. Although the Moon will be above the horizon from most
of Canada, the eclipse is so minor as to be completely invisible to the naked
eye.
July 21-22 - Total Solar Eclipse ( see map,
times, and animation!): To make up
for the anemic lunar eclipse earlier in the month, a major total eclipse of the
Sun occurs two weeks later. The path of the Moon's umbral shadow extends across
India, China, a handful of Japanese islands and the South Pacific Ocean (Espenak
and Anderson, 2008). A partial eclipse is seen within the much broader path of
the Moon's penumbral shadow, which includes most of eastern Asia, Indonesia, and
the Pacific Ocean.
August 05-06 - Penumbral Lunar Eclipse ( see map,
times): A shallow penumbral eclipse occurs 15 days after the total solar
eclipse. Since its magnitude is only 0.402, it will not be visible to the naked
eye.
December 31 - Penumbral Lunar Eclipse ( see map,
times): The last eclipse of 2009 occurs on New Year's Eve. This minor
partial lunar eclipse takes place in Gemini, and is visible primarily from the
Eastern Hemisphere (Figure 8). Greatest eclipse takes place at 19:23 UT when the
eclipse magnitude will reach 0.0763.
Eclipse information from: NASA Eclipse
Homepage, Eclipses
Online (HM Nautical Almanac Office, UK in coordination with the U.S. Naval Observatory)
| Shower |
Activity Period |
Maximum |
Radiant |
Velocity |
r |
ZHR |
Class |
Moon |
| |
|
Date |
S. L. |
R.A. |
Dec. |
km/s |
|
|
|
|
| Antihelion Source (ANT) |
Dec 14-Sep 07 |
- |
- |
- |
- |
30 |
3.0 |
3 |
II |
- |
| Quadrantids (QUA) |
Dec 26-Jan 13 |
Jan 03 |
283°16 |
15:20 |
+49° |
42 |
2.1 |
120 |
I |
6 |
| Alpha Centaurids (ACE) |
Jan 28-Feb 21 |
Feb 07 |
319°2 |
14:00 |
-59° |
56 |
2.0 |
5 |
II |
12 |
| Delta Leonids (DLE) |
Feb 15-Mar 10 |
Feb 25 |
336° |
11:12 |
+16° |
23 |
3.0 |
2 |
II |
0 |
| Gamma Normids (GNO) |
Feb 25-Mar 22 |
Mar 13 |
353° |
16:36 |
-51° |
56 |
2.4 |
4 |
II |
16 |
| Lyrids (LYR) |
Apr 16-Apr 27 |
Apr 23 |
033° |
18:12 |
+33° |
46 |
2.1 |
18 |
I |
27 |
| Pi Puppids (PPU) |
Apr 15-Apr 28 |
Apr 23 |
033°5 |
07:20 |
-45° |
18 |
2.0 |
var |
III |
27 |
| Eta Aquarids (ETA) |
Apr 27-May 23 |
May 07 |
047° |
22:36 |
-01° |
68 |
2.4 |
60 |
I |
12 |
| Eta Lyrids (ELY) |
May 06-May 14 |
May 10 |
050° |
19:22 |
+43° |
43 |
3.0 |
3 |
II |
15 |
| June Bootids (JBO) |
Jun 22-Jul 02 |
Jun 27 |
095°7 |
14:56 |
+48° |
18 |
2.2 |
var |
III |
5 |
| Piscis Austrinids (PAU) |
Jul 15-Aug 10 |
Jul 28 |
125° |
22:44 |
-30° |
35 |
3.2 |
5 |
II |
7 |
| Alpha Capricornids (CAP) |
Jul 12-Aug 08 |
Jul 28 |
125° |
20:20 |
-10° |
24 |
2.5 |
4 |
II |
7 |
| Delta Aquarids (SDA) |
Jul 21-Aug 30 |
Jul 30 |
127° |
22:42 |
-17° |
43 |
3.2 |
20 |
I |
9 |
| Perseids (PER) |
Jul 13-Aug 26 |
Aug 12 |
140° |
03:12 |
+58° |
59 |
2.6 |
100 |
I |
20 |
| Kappa Cygnids (KCG) |
Aug 03-Aug 25 |
Aug 17 |
145° |
19:04 |
+59° |
25 |
3.0 |
3 |
II |
25 |
| Alpha Aurigids (AUR) |
Aug 28-Sep 03 |
Sep 01 |
158°6 |
06:06 |
+39° |
65 |
2.6 |
7 |
II |
11 |
| September Perseids (SPR) |
Sep 06-Sep 13 |
Sep 10 |
168° |
03:12 |
+40° |
65 |
2.9 |
5 |
II |
19 |
| Delta Aurigids (DAU) |
Sep 18-Oct 10 |
Sep 29 |
186° |
05:52 |
+49° |
64 |
2.9 |
2 |
II |
13 |
| Draconids (GIA) |
Oct 06-Oct 10 |
Oct 08 |
195°4 |
17:28 |
+54° |
20 |
2.6 |
var |
III |
18 |
| Southern Taurids (STA) |
Sep 18-Nov 26 |
Oct 11 |
198° |
02:18 |
+09° |
29 |
2.3 |
5 |
II |
21 |
| Epsilon Geminids (EGE) |
Oct 18-Oct 21 |
Oct 20 |
207° |
06:48 |
+28° |
71 |
3.0 |
2 |
II |
2 |
| Orionids (ORI) |
Sep 28-Nov 10 |
Oct 21 |
208° |
06:22 |
+16° |
68 |
2.5 |
23 |
I |
3 |
| Leo Minorids (LMI) |
Oct 17-Oct 27 |
Oct 23 |
209° |
10:40 |
+37° |
61 |
2.7 |
2 |
II |
4 |
| Northern Taurids (NTA) |
Oct 20-Nov 29 |
Nov 13 |
231° |
03:52 |
+22° |
29 |
2.3 |
5 |
II |
25 |
| Leonids (LEO) |
Nov 07-Nov 28 |
Nov 18 |
236° |
10:16 |
+22° |
71 |
2.5 |
var |
III |
1 |
| Alpha Monocerotids (AMO) |
Nov 15-Nov 25 |
Nov 21 |
239°32 |
07:48 |
+01° |
65 |
2.4 |
var |
III |
4 |
| Dec Phoenicids (PHO) |
Nov 28-Dec 09 |
Dec 06 |
254°25 |
01:12 |
-53° |
18 |
2.8 |
var |
III |
18 |
| Puppid/Velids (PUP) |
Dec 01-Dec 15 |
Dec 07 |
255° |
08:12 |
-45° |
40 |
2.9 |
10 |
I |
19 |
| Monocerotids (MON) |
Dec 06-Dec 20 |
Dec 07 |
255° |
06:32 |
+09° |
41 |
3.0 |
2 |
II |
10 |
| Sigma Hydrids (HYD) |
Nov 22-Dec 23 |
Dec 09 |
257° |
08:24 |
+03° |
60 |
3.0 |
3 |
II |
21 |
| Geminids (GEM) |
Dec 05-Dec 19 |
Dec 14 |
262°2 |
07:36 |
+32° |
35 |
2.6 |
120 |
I |
26 |
| Coma Berenicids (COM) |
Dec 10-Jan 25 |
Dec 19 |
268° |
11:40 |
+25° |
64 |
3.0 |
5 |
II |
3 |
| Ursids (URS) |
Dec 16-Dec 25 |
Dec 22 |
270°7 |
14:34 |
+75° |
32 |
3.0 |
10 |
I |
5 |
Information and Table Template Courtesy The American Meteor Society, International Meteor Organization, and Meteors Online.
Shower: named for the constellation or closest star within a
constellation where the radiant is located at maximum activity.
Activity Period: the dates when the ZHR (Zenith Hourly Rates) are
equal to or greater than one.
Maximum: the date on which the maximum activity is expected to occur.
S.L.: the equivalent solar longitude of the date of maximum
activity. Solar longitude is measured in degrees (0-359) with 0 occurring at the
exact moment of the spring equinox, 90 at the summer solstice, 180 at the
autumnal equinox, and 270 at the winter solstice.
Radiant: the area in the sky where shower meteors seem to appear from.
This position is given in right ascension (celestial longitude) and
declination (celestial latitude).
Velocity: the velocity at which shower meteors strike the Earth's
atmosphere. The velocity depends on the angle meteoroids (meteors in space)
intersect the Earth. Meteoroids orbiting in the opposite direction of the Earth
and striking the atmosphere head-on are much faster than those orbiting in the
same direction as the Earth. This velocity is measured in kilometers per second.
r: The Population Index, An estimate of the ratio of the number
of meteors in subsequent magnitude classes. Simply stated: the lower the "r"
value, the resulting overall mean magnitude of each shower will be brighter. "r"
usually ranges from 2.0 (bright) to 3.5 (faint).
ZHR: Zenith Hourly Rate, the average maximum number of shower
meteors visible per hour if the radiant is located exactly overhead and the
limiting magnitude equals +6.5. Actual counts rarely reach this figure as the
zenith angle of the radiant is usually less and the limiting magnitude is
usually lower. ZHR is a useful tool when comparing the actual observed rates
between individual observers as it sets observing conditions for all to the same
standards.
Class: A scale developed by Robert Lunsford to group meteor showers by
their intensity:
Class I: the strongest annual showers with ZHR's normally ten or
better.
Class II: reliable minor showers with ZHR's normally three or better.
Class III: showers with widely variable rates. They may be strong one
year and totally inactive the next.
Class IV: weak minor showers with ZHR's rarely exceeding three. The
study of these showers is best left to experienced observers who use plotting
and angular velocity estimates to determine shower association. Observers with
less experience are urged to limit their shower associations to showers with a
rating of I to III. These showers are also good targets for video and
photographic work.
Moon: the age of the moon in days where 0 is new, 7 is first quarter,
14 is full, and 21 is last quarter. Meteor activity is best seen in the absence
of moonlight so showers reaching maximum activity when the moon is less than 10
days old or more than 25 are much more favorably observed than those situated
closer to the full moon.
Information from the "Observer's Handbook 2009" RASC
