getting to know about stars

2. Overview
Recent advances in space technology have allowed scientists coming from
different background like physics, chemistry, biology, and geology to collaborate on
studying Near-Earth Objects (NEO) like comets and asteroids .
With more powerful telescopes and space probes, the study of comets and asteroids
provides more clues about the origins of our solar system.
Over the past three years, amateur and professional astronomers have discovered
several NEO’s that came close to Earth, the most recent asteroid being Asteroid 2012
DA14.
It made a very close approach to Earth as it orbited the Sun on February 16, 2012
(Philippine Time).
On the morning of February 16, 2012, an asteroid entered Earth’s atmosphere and
exploded over Lake Chebarkul in Russia hurting about 1,000 people in the process.
These two events triggered superstitions, fears, and doomsday prophecies held by
different cultures. But do these things have scientific basis?

3. HAS EARTH EVER BEEN
HIT BY A COMET OR AN ASTEROID?
IF YES, HOW HAVE
SOME IMPACTS AFFECTED EARTH?
HOW OFTEN DOES
A COMET OR AN ASTEROID HIT EARTH?

4. comets

5. Comets and asteroids are referred to be
astronomers as Near-Earth Objects (NEO).
Comets
-are icy bodies or objects while asteroids are rocky
fragments.
-they are remnants from the formation of our solar
system 4.6 billion years ago.
The table summarizes the similarities and
differences between a comet and an asteroid.

6. As you can see in the table, comets and asteroids have irregular
shapes and varied sizes.
-They both reflect light from the Sun at varying amounts depending on
the size and composition.
-The presence of more silicates allows a comet or asteroid to reflect
light.
Silicates -are minerals that contain the elements silicon, oxygen, and at
least one metal.
If an asteroid has smaller amounts of silicates relative to its other
components, it would be more difficult to see it even with a telescope
because only a small area of the asteroid can reflect light thus it may
appear smaller than what it really is when viewed.

7. Characteristic Comet Asteroid
Origin Kuiper Belt and Oort Cloud Main Asteroid Belt
Shape Varied/Irregular Varied/Irregular
Size range of diameter
(kilometer)
1 – 10 (nucleus only) 1 – 100 ++
Chemical composition Ice (frozen water); frozen gases
(ammonia, methane, and carbon
dioxide); other organic compounds
(Carbon – containing compounds)
Orbit Highly elliptical More rounded
Orbital period (years) 75 to 100,000++ 1-100
Table 1. Comparison of some characteristics of comets and asteroids

8. Comets
A Comet is a small body of ice, rock and cosmic dust
loosely packed together in a highly elliptical orbit
around the sun.

9. Structure of a Comet
To Sun
Ion Tail
Dust
Tail
Coma
Comet Structure
• Nucleus
• 10 km “Dirty Snowball”
• Coma
• Cloud of evaporated ices and ions
• may be 100,000 km in diameter
• Tail
• Always points away from Sun
• Solar Wind and Radiation Pressure

10. Tail always points away from
Sun because of solar wind and
radiation pressure

11. ?
Nucleus
10 km “Dirty Snowball”

12. Comet and asteroid both orbit the Sun and move relatively slow
when viewed from Earth. This means, you can see a comet for up to a
year in the night sky (or even during the morning if the comet is bright
enough).
Comets usually come from the
Oort Cloud which is beyond our
Solar System, and a few from Kuiper Belt which
is just beyond Neptune’s orbit. Long-period
comets come from the Oort Cloud,
while short-period comets come from Kuiper
Belt.

13. The Oort Cloud
In 1950 Jan Oort
-noticed that no comet has been observed
with an orbit that indicates that it came from interstellar space,
there is a strong tendency for aphelia of long period
comet orbits to lie at a distance of about 50,000 AU, and
there is no preferential direction from which
comets come.

14. Comet Halley, the most famous comet of the 20th century
is the only known short-period comet. It takes 75-79 years for Comet Halley to orbit
the Sun. we see it in the sky every time it makes its
nearest approach to the Sun. All other comets that have been identified are classified
as long-period comets and takes 200 to hundred millions of years to complete their
orbit around the Sun.
Asteroids, on the other hand, originate from the Main Asteroid Belt between Mars and
Jupiter. This belt is theorized by scientists to be remnants of a planet that did not
completely form.

15. Comet Halley 1910
•POPE CALLIXTUS III
EXCOMMUNICATED HALLEY'S
COMET IN 1456
•IN 1910, CHARLATANS SOLD
"COMET PILLS"

16. Bayeaux Tapestry
Norman Invasion of 1066

17. Comet of 1577

18. Two Showers for Halley

19. Comet Hale-Bopp
Comet Hale-Bopp, which made its closest approach to the Sun
in April 1997, was one of the largest and brightest comets of the second
half of the 20th century, even though its closest approach to the Earth was
still relatively distant.
A very long-period comet, it had no previous known history in
human observation, and will not be seen again by humans for thousands
of years.

20. Bennett's Comet
In 1970 the South African amateur astronomer J.
Bennett observed this brilliant comet.
A computer technique called isopoda
mapping has enhanced this image by
assigning different colors to the various grey tones
in the original black and white photograph. The comet's long
gaseous tail is clear to see.

21. The return of Halley's Comet
Halley's Comet reappears approximately
every 76 years. This photograph, taken
in New Zealand in 1986, shows the comet
during its most recent approach to the Sun.

22. Comet Hyakutake
Comet Hyakutake reached its closest point to Earth in its
path through the inner Solar System on March 25, 1996.
The comet was bright enough to be seen with the naked eye.

23. Comet
West

24. A Tale of Two Tales
ION TAIL (top, blue): ionized gas pushed away
from the Sun by the solar wind.
DUST TAIL (bottom, white): fine dust pushed
away from the Sun by radiation pressure.
A Tale of Two Tales

25. Edmond Halley
The astronomer and
mathematician Edmond Halley
was the first person to calculate
the orbit of a comet. He believed that
comets travelled in elliptical
orbits around the Sun. This was
proved to be correct with the return,
in 1758, of what is now
known as Halley's Comet.

26. Skylab
In 1973 the United States
-launched the space station Skylab.
This photograph of Skylab was taken over
the Earth on February 8, 1974, by the fourth
group of astronauts to occupy the space
station. They took the photograph from
their Apollo spacecraft as they prepared to
return home. The sheet of g
old-colored material stretched over the
station is a makeshift Sun shield
that the second group of astronauts to
occupy Skylab set up. It replaced a Sun and
micro-meteoroid shield that fell off during
launch. Skylab operated for six years.

27. asteroids

28. asteroids
• When the solar system came together about 4.6 billion years ago, many lumps
of rock did not become part of any of the planets. These bits and pieces have
continued to orbit round the Sun. Sometimes they smash into each other and
break into smaller pieces. Sometimes they crash into planets as meteorites. A
few have been captured as moons, mainly by Jupiter. But thousands still
wander round the Sun. They are called minor planets, planetesimals or
asteroids.
• Most of the asteroids we know about are in a wide belt between the orbits of
Mars and Jupiter. Another belt of small, icy objects lies at the outer reaches of
the solar system, far beyond Neptune, called the Kuiper Belt. Other asteroids
are sprinkled thinly between the orbits of the planets.

29. Asteroids
Asteroids are made of rock,
metal, or a combination of
both.
They range in size from one metre
( or perhaps smaller ) up to 1000km.

30. Asteroids have different shapes. Big ones are usually round, but
small ones are all sorts of knobby shapes, and sometimes look like
potatoes.
They have craters where smaller rocks have crashed into them. Some
asteroids form pairs going round each other as they orbit the Sun, in
the same way as the Earth and Moon.
Some have been given names, such as Eros, Hermes, Vesta, Chiron and
Ida, but most are listed by numbers. Most are dark in color because
they have a lot of carbon.
These have not changed much since they were formed.
Some contain iron and other minerals and seem to have been melted in
the past.

31. • A number of asteroids cross the path of the Earth. That means we might be hit
by one of them. If a big asteroid collided with the Earth, the results would be
catastrophic. Big meteorites have crashed into the Earth several times in the
past. One may have caused the death of the dinosaurs, 65 million years ago.
Such collisions are very rare, but they do happen.
• Eros is one of the asteroids near Earth. The Near Earth Asteroid Rendezvous
(NEAR) spacecraft, sent by NASA (the National Aeronautics and Space
Administration) went into orbit around Eros in 2000, and became the first
spacecraft to land on an asteroid. It sent back pictures of Eros’s pitted and
grooved surface, and information about what it is made of. Finding out more
about asteroids will help us to predict what might happen if one did hit the
Earth. Many scientists think that governments should set up a shared system
that would knock an asteroid off course if it came towards us.

32. Asteroid Belt
Asteroids are mostly in the asteroid belt between Mars and Jupiter.

33. Asteroid Orbits
Asteroids are strongly influenced by the gravity of
Jupiter

34. Asteroids Elsewhere

35. The orbit of an asteroid is more rounded and less elliptical than
the orbit of a comet.
In February 2013, Asteroid 2012 DA14
-made a very close approach to Earth as it orbited the Sun.
Distance in spaced is measured in light years and this Asteroid was just
0.4 light year away from Earth; the closest that any asteroid has ever
been close to Earth.
In December 2012
-during the midst of the dooms day prophecies, Asteroid Toutatis
also made a near approach to Earth but not as close as Asteroid 2012
DA14

36. Three asteroids
• This composite image shows the asteroids Mathilde, Gaspra and Ida. Mathilde,
left, was photographed by the Near Earth Asteroid Rendezvous (NEAR) space
probe in 1997. Gaspra and Ida, centre and right, were photographed by the
Galileo space probe in 1991 and 1993, respectively, and are smaller and more
oblong-shaped than Mathilde. The three asteroids are partially obscured by
shadows.

37. At least 1.1 million asteroids larger than 1 km
in the main Asteroid belt around the Sun .

38. Taking a Close Look
TAKING A CLOSE LOOK

39. The discovery of high contents of iridium in oceanic sedimentary layers in different
parts of the world such as Italy, Denmark, and New Zealand during the late 1970’s led
geologists.
Luis and Walter Alvarez
- propose the Alvarez Hypothesis in 1980.
Iridium
-is a metal belonging to the Platinum family. It is a very rarely found in Earth’s crust,
but more abundant in the mantle and core. It is also abundant in our solar system.
They proposed that an asteroid with approximately 10 kilometers in diameter made
impact with Earth 65 million years ago. They thought that the impact caused material to be
thrown up in the air, thus blocking sunlight, and brought about a period of winter long
enough to cause a mass extinction of plants and animals, including the dinosaurs. Further,
this event ended the Cretaceous Period and ushered in the Tertiary Period.

40. METEORS

41. Have you ever seen a shooting star in the night sky?
It appears as an object with a tail just like a comet.
It travels quickly and appears to fall on the ground. A shooting
star is another name for meteor.
But the truth is: a meteor is not a star at all. Meteor is a light
phenomenon or a steak of light that occurs when a meteoroid
burns up as it enters Earth’s atmosphere.
Meteoroid is a broken up rock and dust from either a comet,
asteroid, the Moon, or from Mars.

42. Meteoroid
- can be as small as grain of sand or as big as a boulder.
When it enters Earth’s atmosphere, the air in front of the meteoroid
heats up, causing materials to burn up. From Earth, these glowing materials
appears as a streak of light or a fast-moving bright object that appears to have a
tail just like a comet.
-what differentiates the two when we see them in the sky is that a comet moves
slowly and appears in the sky for a longer time.
- usually all burns up when it enters Earth’s atmosphere. But when a fragment is
now called a meteorite.
- meteorite exploding over Russia in February 2013 , their use of the word
meteorite inaccurate. Instead, a meteoroid exploded over Russia.
-the space fragments they collected on the ground is the meteorite.

43. Meteor
- moves swiftly and seems to fall on the ground.
-it “shoots” from a point in the sky, making people think that
it is a shooting or falling star.
Also, a comet is difficult to see with the unaided eye
because it is farther from Earth compared to a meteoroid
entering Earth’s atmosphere.
Sometimes, a comet can be bright enough to seen by
the unaided eye, but this is rare, just like in the case of
Comet Hale-Bopp.

44. When Earth orbits the Sun and passes through the orbit os a comet
where these comet fragments are found, we observe many streaks of light
from Earth which is called a meteor shower.
During a meteor shower, meteors seem to originate from only one
point in the sky because the meteoroids are travelling in parallel paths with
the same velocity.
Meteor Shower
- is named after the constellation where they seem to originate from, but
this does not mean that the meteoroids come from the associated
constellation.
REMEMBER:
A meteor and a meteor shower are light phenomena; they are not
stars.

45. The Cause of Meteor Showers

46. Why after midnight is best?
Rotational
Velocity
Orbital
Velocity
Midnight

47. The Leonid meteor storm of
1833
On the night of November 12-13,
1833, the annual Leonid meteor shower
unexpectedly turned into a raging storm
of up to 150,000 meteors per hour—some
40 per second—all appearing to
radiate from a single point in the
constellation Leo (hence the shower's
name). It was the greatest meteor
storm in recorded history. It was terrifying
in its ferocity, and caused
widespread panic where it was
visible in the eastern United States.

49. The 1966 storm

50. 1997 Leonids from Orbit

51. Meteor Crater
Meteor Crater in Arizona in the United States was created about 50,000
years ago by a meteorite up to 50 meters in diameter. The crater is some 1,200
meters across and about 180 meters deep. For many years it had been
thought that the crater had been caused by a volcano. It was finally
identified as having been caused by a meteoric impact by the
geologist and astronomer Eugene Shoemaker in the 1950s.
It was the first large crater on Earth to be identified as an impact feature.

52. An iron meteorite 100 feet across and 70,000 tons slammed into
the Earth at about 43,000mph in the Arizona desert near Flagstaff
40,000 years ago. Bar ringer Crater is 4,100 feet wide and 571 feet
deep.
Large Impact Craters Crater

53. Other Impact Craters

54. Tunguska, 1908

55. Sporadic Meteors
Irons Stony-Irons
Chondrites Carbonaceous
Chondrite
Achondrite

57. Comets Hitting Earth

58. The number of meteors that can be seen
during a meteor shower vary. It starts with the
appearance of a few meteors per hour, increasing in
frequency until it reaches its peak of 1-2 meteors per
minute, and then declines. The table shows some of
the more famous annual meteor showers and the
month when they reach their peak. The dates in
the peak month vary and astronomers make forecasts
of the peak days (usually lasting for three days.

59. Month Source of
meteoroid
Name of the
Meteor Shower
Constellation
(where the meteor shower
seem to come from)
August Comet Swift-Tuttle Perseid Perseus
October Comet 21P/Giacobini-
Zinner
Draconid Draco
October Comet Halley Orionid Orion
November Comet Tempel-Tuttle Leonid Leo
November Comet Encke Taurid Taurus
December Asteroid 3200
Phaethon
Geminid Gemini
Table 2. Some examples of Famous Annual Meteor Showers

60. Usually, the meteoroids that cause meteor showers
come from comets, but they may also come from
an asteroid like in the case of the Geminids.
Earth passes through Asteroid3200 Phaethon’s orbit
where some fragments from the asteroid are found.
Once these fragments enter Earth’s atmosphere,
they burn up as well.
Meteoroids from comets appear fuzzy
because of the ice particles while those from asteroids are
clearer and distinct because they do not have these ice
particles.

61. Meteorites are of importance to scientists in studying the
occurrence of different elements and compounds on Earth.
This information is in turn important in studying our mineral
resources which is an important industry in any country.
Generally, there are three types: stony, stony-iron, and
iron meteorites. In the Philippines, there are only five
meteorites that have been accepted internationally.
The table enumerates this meteorites.

62. Meteorite Year of
Discovery
Place
Discovered
Type Chemical Composition
Pampanga 1859 Pampanga Stony Iron-Nickel (7-11%); Ferrous sulfide (FeS); Magnesium
Iron silicate (a.k.a. olivine or (Mg, Fe)₂SiO₄); Calcium-
Aluminum intrusion (Ca-AI); pyroxene or XY (Si,
AI)₂O₆(X can be calcium, sodium, iron⁺2 and
magnesium and more rarely zinc, manganese and
lithium; Y represents smaller-sized ions like chromium,
aluminum, iron⁺3, magnesium, manganese, scandium,
titanium, vanadium and iron⁺2
Paitan 1910 Paitan, Ilocos Stony Iron; Magnesium iron silicate (a.k.a. olivine or (Mg,
Fe)₂SiO₄); pyroxene
Calivo 1916 Western Visayas Stony Not yet determined
Pantar 1938 Central
Mindanao
Stony
meteorite
Iron; Magnesium iron silicate (a.k.a. olivine or (Mg,
Fe)₂SiO₄); pyroxene
Bondoc 1956 Southern Tagalog Stony-iron Metallic iron-nickel; silicates (olivine and pyroxene)
Table 3. Five Meteorites Found in the Philippines (Internationally Validated)

63. THANK YOU FOR LISTENING!

64. Comets,
asteroids,
and meteors