1. PERSEIDS
-Equinox Astronomy Club of IIT Guwahati1

2. METEOROID
 A meteoroid is a small rocky or metallic body
travelling through space. Meteoroids are
significantly smaller than asteroids, and range in
size from small grains to 1 meter-wide
objects. Most are fragments from comets or
asteroids, while others are collision impact debris
ejected from bodies such as the Moon or Mars
2

3. METEOR SHOWER
 The visible streak of light from space debris is the
result of heat as it enters a planet's atmosphere,
and the trail of glowing particles that it sheds in its
wake is called a meteor, or colloquially a "shooting
star" or "falling star".
 A series of many meteors appearing seconds or
minutes apart, and appearing to originate from the
same fixed point in the sky, is called a meteor
shower.
3

4. METEOR STORMS
 Intense or unusual meteor showers are known
as meteor outbursts and meteor storms, which
may produce greater than 1,000 meteors an hour.
4

5. METEOR
5

6. RADIANT POINT
 Because meteor shower particles are all travelling
in parallel paths, and at the same velocity, they will
all appear to an observer below to radiate away
from a single point in the sky.
 caused by the effect of perspective.
 This "fixed point" slowly moves across the sky
during the night due to the Earth turning on its axis
6

7. RADIANT DRIFT
 The radiant also moves slightly from night to night
against the background stars due to the Earth
moving in its orbit around the sun.
7

8. NOMENCLATURE
 Meteor showers are almost always named after the
constellation from which the meteors appear to
originate.
 Meteor showers are named after the nearest bright
star with a Greek or Roman letter assigned that is
close to the radiant position at the peak of the
shower, whereby the grammatical declension of the
Latin possessive form is replaced by "id" or "ids".
Hence, meteors radiating from near the star delta
Aquarii (declension "-i") are called delta Aquariids.
8

9. THE ORIGIN OF METEOROID STREAMS
 A meteor shower is the result of an interaction
between a planet, such as Earth, and streams of
debris from a comet.
 Each time a comet swings by the Sun in its orbit,
some of its ice vaporizes and a certain amount of
meteoroids will be shed. The meteoroids spread out
along the entire orbit of the comet to form a
meteoroid stream, also known as a "dust trail" (as
opposed to a comet's "dust tail" caused by the very
small particles that are quickly blown away by solar
radiation pressure).
9

10. THE ORIGIN OF METEOROID STREAMS
 Recently it has argued that most of our short-period
meteor showers are not from the normal water
vapor drag of active comets, but the product of
infrequent disintegrations, when large chunks break
off a mostly dormant comet.
 Examples are the Quadrantids and Geminids,
which originated from a breakup of asteroid-looking
objects 2003 EH1 and 3200 Phaethon, respectively,
about 500 and 1000 years ago. The fragments tend
to fall apart quickly into dust, sand, and pebbles,
and spread out along the orbit of the comet to form
a dense meteoroid stream 10

11. PERSEID METEOR SHOWERS
 The most visible meteor shower in most years are
the Perseids, which peak on 12 August of each
year at over one meteor per minute associated with
the comet Swift-Tuttle which last passed near the
Earth in 1992.
 Comet Swift-Tuttle won't be visiting our neck of the
woods again until the year 2125
 The Perseids are so-called because the point from
which they appear to come lies in
the constellation Perseus.
 Discovered in 36 AD (first record)
11

12. PERSEID METEOR SHOWERS
 Every meteor is a speck of comet dust vaporising
as it enters our atmosphere at 36 miles per second.
 They mostly appear as fleeting flashes lasting less
than a second, but the brightest ones leave behind
trails of vaporised gases and glowing air molecules
that may take a few seconds to fade.
 The peak activity will be from 11:45 pm IST on
August 12 to 2:15 am IST on August 13.
 In early medieval Europe, the Perseids came to be
known as "tears of St Lawrence"
12

13.  In 1839, Eduard Heis was the first observer to take
a meteor count and discovered that Perseids had a
maximum rate of around 160 per hour.
 Measured in Zenithal Hourly Rate (ZHR) is the
number of meteors a single observer would see in
one hour under a clear, dark sky (limiting apparent
magnitude of 6.5) if the radiant of the shower were
at the zenith.
13

14. THIS YEARS SHOWER
 The Perseid meteor shower peaks this year when
there's almost no moon, affording a dark sky for
late-night meteors spectators and counters. A thick
waxing crescent moon sets around mid-evening,
posing little interference to this year's showers
 This event is for the unaided eyes, and enthusiasts
will be able to see the meteor shower in the north-
eastern part of the sky. The view will be even better
with a pair of binoculars
14

15. CALCULATION OF ZHR
 The formula to calculate the ZHR is:
 where
represents the hourly rate of the observer. N is the
number of meteors observed, and Teff is the
effective observation time of the observer.
 Example: If the observer detected 12 meteors in 15
minutes, their hourly rate was 48. (12 divided by
0.25 hours). 15

16. CALCULATION OF ZHR
 This represents the field of view correction factor, where
k is the percentage of the observer's field of view which
is obstructed (by clouds, for example).
 Example: If 20% of the observer's field of view were
covered by clouds, k would be 0.2 and F would be 1.25.
The observer should have seen 25% more meteors,
therefore we multiply by F = 1.25.
16

17. CALCULATION OF ZHR
 This represents the limiting magnitude correction factor.
For every change of 1 magnitude in the limiting
magnitude of the observer, the number of meteors
observed changes by a factor of r. Therefore we must
take this into account.
 Example: If r is 2, and the observer's limiting magnitude
is 5.5, we will have to multiply their hourly rate by 2 (2 to
the power 6.5-5.5), to know how many meteors they
would have seen if their limiting magnitude was 6.5.
17

18. CALCULATION OF ZHR
 This represents the correction factor for altitude of
the radiant above the horizon (hR). The number of
meteors seen by an observer changes as the sine
of the radiant height in radians.
 Example: If the radiant was at an average altitude
of 30° during the observation period, we will have to
divide the observer's hourly rate by 0.5 (sin 30°) to
know how many meteors they would have seen if
the radiant was at the zenith.
18

19. EXTRATERRESTRIAL METEOR SHOWERS
 Any other solar system body with a reasonably
transparent atmosphere can also have meteor
showers. For instance, Mars is known to have
meteor showers.
 http://leonid.arc.nasa.gov/estimator.html
19

20. THE 2010 PERSEIDS OVER THE ESO'S VLT
20

21. A PERSEID IN 2007.
21

22. ITALY
22

23. THANK YOU
23