Welcome to Visual Astronomy
or
Astronomical Observing
Based mainly on observation with binoculars

By Alain Dussault

Comets, Oort cloud, Eclipses
Meteoroids or shooting stars and Asteroids

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Comets

These sites concern comets:

http://comets.amsmeteors.org/
http://encke.jpl.nasa.gov/

Sometimes, a diffuse object become visible in the sky. It may look like a blob. If we are lucky, this blob will develop and become more brilliant over a period of time from weeks or months, and develop a tail. The tail can become very long. We have seem two such comets in the last two years. Comets are composed mainly of a dirty mass of ice.

Many comets travel from the far end of our solar system to up to entering our solar system. They formed itself from unused matter from the formation of the solar system. This part of the universe where its form, is know as the Oort cloud.

Each year, amateur astronomers discover or rediscover a dozen comets, many of which do not become much brilliants. To each new found, a nomenclature is given as per example:

C/1995 O1 (Hale-Bopp) or C/1996 Q1 (Tabur).

Following is the official designation of the International Astronomical Union for comets:

A= first half of January

B= second half of January 
C= first half of February 
D= second half of February 
... and so on. The letters I and Z are not used
    (24 half month per year)

C/1995 O1(Hale-Bopp)

|  |  | |  +- Names of discoverers
|  |  | +---- First comet in the first half of July
|  |  + ----- First half of July of 1995
|  + -------- As you have deduct: in 1995
+------------ C for long period comet
              Short period, letter P)

C/1996 Q1 (Tabur)

|  |  | |  +- Name of discoverer
|  |  | +---- first comet in first half of August
|  |  + ----- First half of August of 1996
|  + -------- Year of discovery
+------------ for long period comet

Oort Cloud

This the part of the far sky from where most of the comets come from.

Eclipses

Here are some sites concerning eclipses:

http://www.skypub.com/eclipses/eclipses.shtml
http://planets.gsfc.nasa.gov/eclipse/eclipse.html
http://www-clients.spiritnet.au/~minnah/LEO.html

Eclipses phenomena are of two natures. We can have a partial or complete eclipse of the Sun, or a partial ot total eclipse of the Moon.

There are also eclipses between satellites of big planets. But there events are observables only with a telescope of a telescope of 4 inches or more of aperture. Only the events for the Jupiter satellites are available in specialized software like Guide 6 or Meridian, and also in Sky & Telescope.

Sun Eclipses

A partial or total eclipse of the Sun is caused by the passing of the Moon directly between the Earth and the Sun.

If the Moon is nearer the Earth, then the its apparent diameter is greater than the apparent diameter of the Sun. We assist then at a total eclipse of the Sun, a great nature spectacle, something that one must witness in it lifetime.

But if the Moon, passe further form the Earth, we see then at an annular eclipse of the sun. In effect, the apparent diameter of the Moon is then smaller than the apparent diameter of the Sun, we then see the peripheral ring of light of the Sun.

To be able to observe the Sun, during such an event, we must have special filter for our instruments or special glasses.

WE SHOULD NEVER LOOK AT THE SUN WITH OUR NAKED EYES

Moon Eclipses

A partial or total eclipse of the Moon happen, when the Moon pass directly in the shadow projected by the Earth, in space.

Here again, we assist, if it is a total eclipse, to a very interesting spectacle of nature. The Moon change color.

We can observe an eclipse of the Moon with our naked eyes or with binoculars or with a telescope. With an instrument we can see when the shadow of the Earth arrive at different relief on the Moon. Amateurs used to time these events.

Meteoroids

A meteor, also called shooting star, is a trace of light appearing in the sky when a fragment of rock coming form space enter the atmosphere of the Earth at about 40 km/s. the heat cause by air friction render the object incandescent.

So much as these objects stay in space, we called them meteoroids. If it happen to enter the Earth atmosphere, then it is called meteorite.

There are swarm of meteoroids that turn around the Sun, in the orbits of comets. Some of these orbits cross the Earth orbit. Each time the Earth pass at these crossing points, the numbers of meteorites observed will increased. In these events, the meteorites seem to come from a precise point of the sky and their luminous trails converged from that point called radiant.

Principal Meteor showers

Date	Month	Radiant Name	Number visible	Length (d)
4	January	Quadrantids	40	2.2
21	April	Lyrids	15	4
4	May	Eta Aquarids	20	6
28	July	Delta Aquarids	20	14
12	August	Perseids	50	4.8
21	October	Orionids	25	4
3	November	Taurids(south)	15	?
16	November	Léonids	15	?
13	December	Géminids	50	5.2
22	Decembee	Ursids	15	4

Asteroids

Between the planets Mars and Jupiter, there are a lot of small planets, named asteroids.

The most brilliant asteroids

Sites for asteroids are:

The number that is before the name of the asteroid, represent the chronological order of the discovery. The first discovered was Ceres, the second one Pallas and so on...

Preceding chapter, The Color of stars...

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Last update August 1st, 1999.