meteors are just sand grain-sized objects hitting the
atmosphere. Sometimes a big one the size of a pebble
causes a chorus of "ah"s
at a star party - the brilliant flash is quite stunning.
Normally, when the skies are dark, we can see perhaps five
sporadic meteors per hour.
certain dates every year, we can see many more than that.
That is because the Earth crosses an orbit of debris
from a comet. All these meteors seem to come from the
same spot in the sky because that is the direction the
debris comes from. Hence meteor showers are named after
the constellation where they seem to come from.
time when the most meteors can be seen is about two hours
before sunrise. In the morning our planet is facing the
direction we are moving around the Sun.
is a list of the best meteor showers. The Perseids in
August is the shower most often watched.
it appears to come from
of peak of shower
per hour if very dark sky
19 - May 28
21 - 22
22 - Jul 2
17- Aug 24
14- Nov 21
up to thousands
7 - Dec 17
Moon orbits the Earth, but at a tilt of 5 degrees compared
to the Sun. When the Moon's phase is new, its shadow
usually misses the Earth, when the phase is full, the
Moon usually misses our shadow. When the three directly
line up, we have an eclipse.
a lunar eclipse, about half the planet can see the full
Moon get 100 times darker over a few hours. The Moon
has a reddish glow because the light striking the
Moon passes through the edge of the Earth's atmosphere.
eclipses are less frequently observed and more dramatic.
For most people, the Moon just covers part of the Sun.
often not even noticed unless you look through special
eclipse glasses, or watch the round dapples of light
through trees turn into crescents.
those in the narrow path of the Moon's full shadow
witness one of nature's grandest spectacles. During
the total eclipse phase, the sky gets dark, it gets cooler;
bright stars can be seen and nocturnal animals wake up.
You can watch the total phase with binoculars or your unaided
eyes - the haunting
corona which is hotter than the Sun, solar flares, and
shadow bands on the ground. At any other time, it is not
safe to look at the Sun without a proper solar filter that
is known to be safe.
are predicted many years in advance; and several companies
and RASC Centres sponsor tours.
form of eclipse is a transit, when a planet crosses the
disc of the Sun. Mercury will transit on May 9, 2016,
Venus will transit on June 6, 2012 with a 105-year wait
for the next transit after that.
of planets orbiting other stars have been observed. It
is a promising technique to find Earth-sized extrasolar
planets. Many stars need to be continually observed to
find the several hour long slight darkening caused by
a transit of an Earth-like planet. If that repeats at
regular intervals, a planet has been located. The Kepler
Mission will watch many stars near the constellation
Cygnus for several years to look for planets.
are 0.1- to 40-km diameter objects made mostly of dust,
ice, and dry ice. They make strange journeys around
the Sun, spending years moving slowly far away, then
coming closer for a quick pass, then returning back
to the frozen outer reaches of the Solar System.
However, some short-period comets return every few
a comet gets closer to the Sun, more dry ice vaporizes
and the comet releases more dust. The solar wind pushes
the dust away from the Sun to make a tail.
Some comets return at predictable times. Halley's
comet was / will be near the Sun in 1910, 1986, and 2061.
comets just appear out of the blue. Comet McNaught was
discovered in August 2006, was visible in Canada during
early January 2007 (even during daytime), then it passed
into the southern hemisphere with
a stunning tail as shown here. Comets are
named after their discoverers.
knows what comets will be discovered in the next few
Aurorae (also known as the Northern Lights and Southern Polar
Lights) happen because of events on the Sun, which affect
the Earth a few days later. The Sun always gives off
particles, but at times, a solar flare gives off many
more particles than normal. When these hit the Earth's
atmosphere, the glow of aurora can be seen widely.
take pictures of aurorae, use a tripod and the widest-angle
lens you have at the highest ISO setting and widest aperture.
An exposure of ISO 800 at f/5.6 for 30 seconds will show
aurorae and their bright colours. Details of changing features
show up better on short exposures.
digital cameras, the automatic focus will not work for
astronomical objects. Change to manual focus and turn
the focusing ring to focus (while wearing any distance
glasses) on a sharp distant object, such as a light a
few hundred meters away. If such an object
is not available, turn the focusing ring to the "infinity" setting.
much larger than the Sun will eventually blow up in so-called "supernova" explosions
which, for a short time, give off as much energy as
the rest of their parent galaxies altogether.
our size typically have about one supernova per century.
The last bright Milky Way supernova was almost 400 years
ago, although the Large Magellanic Cloud (a satellite
galaxy to the Milky Way) had a supernova 1987. It was first
reported by Ian Shelton, a Canadian astronomer. People
in the southern hemisphere could see a new bright star
where only a faint star had been seen earlier. After a
few months, supernovae fade.
Star Finder shows three stars large enough to become
supernovae - Betelgeuse, Spica and Antares. One of them
might already have exploded. They are all hundreds of
light years away. It takes that many years for information
to reach us by light, radio waves and gamma rays.
are important for the history of the galaxy and planets,
because heavy atoms like iodine and gold can only be
made in supernovae. Some of the mass in the Sun and our
Solar System and our bodies originated in supernovae.
type of supernovae typically has the same brightness.
Careful observation of these particular events allows astronomers
to calculate the distance to far-away galaxies. Astronomers
were very surprised to find that distant galaxies appear
to be moving away from us much faster than expected. The
cause of the "dark
energy" driving this acceleration is still a mystery.