Asteroids are the flotsam and jetsam of the part of the Solar System
in which the main planets orbit. The majority of them actually inhabit
the region between the orbits of Jupiter and Mars and range in size from
about 600 miles in diameter down to a few tens of feet across. The
largest one, known as Ceres, is no longer classified as an asteroid
as such, having been promoted to the class of dwarf planet because of
its size.image at the same time of night when Mars is close to its highest point in the
sky, it will take Mars another 40 minutes to rotate back to the same point it
presented the night before. Over subsequent nights at the same time, you
slowly get to see a small amount of new surface detail before the planet
rotates into the same position it started from the night before.Asteroid Belt
Beyond Mars lie the main belt asteroids, tens of thousands of them. There is
a book by a well-known writer called G.F.D. Chambers, the first astronomical
book PM read at age seven. In this book Chambers refers to the asteroids,
and says,“They are of no real interest to the amateur observer, and they
are in fact of no interest to anybody!” He could not have been more wrong.
We can learn a great deal from the asteroids. In 2011 the spacecraft Dawn
entered orbit around Vesta, the third-largest asteroid, to conduct a survey
before heading for Ceres, now ranked as a dwarf planet.
All the large asteroids keep well clear of the Earth but smaller ones do not
and some have been known to pass between the Earth and the Moon. There
is always a danger we will be hit by one, with catastrophic results. There
is no difference between a large meteorite and a small asteroid. Amateur
astronomers are experts in photographing the Near Earth Asteroids so their
orbits can be worked out and we know when to expect them.
We have to admit that if we saw a mile-wide asteroid approaching us we
could do nothing about it. Once PM had a letter from a lady asking what to
do in the event of an imminent impact from an asteroid. He replied, “Repeat
after me ... Our Father...” However, the chances of this happening in our time
are very low.
The brightest asteroid, though not the largest, is Vesta, roughly 300 miles
in diameter. In 2011 the probe Dawn went into a path around it and returned
photos showing a rough cratered surface with one huge impact crater near
the pole. Having made a survey, the Dawn probe will go on to Ceres. As
it'll take some time to get there, we cannot expect any significant results to
appear before about 2015.[10] Diagram shows the process of
combining a red [R] filtered image with
a blue [B] one, using half from each to
produce a synthetic green [(G)]. These
three components are then combined
to produce an R(G)B image as shown
in the lower left. Finally, adding the
R back in as a luminance layer and
tweaking the result gives a very
detailed image of Mars.
[11] Comet Tempel 1 impacted by the
probe Deep Impact.1110Astronomer Book