SPA Planetary Section

Asteroid Projects

Recommended equipment:- Binoculars such as 10 x 50 models are suitable.

Guissepe Plazzi made the first discovery of an Asteroid (or Minor Planet) Ceres in 1801. Today about 5,000 asteroids have been catalogued of which Ceres about 1000 km diameter is the largest, the smallest being Hather only 0.5 km dia. It is estimated there are 40,000 asteroids exceeding 1.0 km dia. and countless numbers of lesser fragments. Like the five bright naked eye major planets Mercury, Venus, Mars Jupiter and Saturn, some asteroids, including Ceres, travel around the Sun in orbits around the Sun an a distance of approx. 2.8 AU (Astronomical Units) generally complying with the Titus-Bode Law devised in 1772. Some asteroids orbit the Sun but are obedient to Jupiter, travelling in tracks ahead, others behind the Giant Planet. A few asteroids come close to or even within the Earth's orbit and in aeons of time past many may have collided with the Earth, the Moon and other planets and some astronomers believe such a collision may have caused the extinction of the Dinosaurs, 65 million years ago.

At appropriate times several asteroids can be observed using quite ordinary hand held binoculars (though use of a tripod provides a better steady image). Indeed Vesta, which vies with the probably marginally smaller Pallas as being the second largest asteroid can occasionally be seen by naked eye. Large telescopes reveal many more asteroids, but even at quite high magnification asteroids only appear like stellar points of light. Binoculars are compact, convenient to use and provide wide fields of view are ideal for observing the brighter asteroids of which four are ideal subjects for SPA members projects.

Name    Year of   Sidereal Mean Distance  Orbital inclination Diameter  Best apparent
       Discovery   Period    from Sun         in degrees       in km   brightness (Mag)

Ceres   1801       4.6 yr     2.77 AU           10.6           1000         +6.7
Pallas  1802       4.62       2.77              34.8            540         +6.7
Juno    1804       4.36       4.36              13.0            250         +7.4
Vesta   1807       3.63       2.36               7.1            550         +5.2

The first problem for potential observers is to find the asteroid. Andy Hollis, Director of the BAA's Remote Planets and Asteroid Section has provided guidance and Finder / Comparison Star charts (drawn by John Toone) for asteroids when suitable as SPA projects. Finder charts are provided to SPA planetary Section members (who supply suitable SAE with their requests). Observers usually find asteroids by Star Hopping, first observing an easy bright star in the sky near to the asteroid, then moving in stages checking the identity of more stars until the suspect asteroid is found. Then make a drawing, say representing the binoculars field of view with a 80 mm circle on A4 paper, showing the position of the asteroid and all or at best as many of the stars visible in the binoculars. Observers should make sure they can subsequently easily identify the field of their sketch, if needs be making supplementary sketches. The observer needs to confirm having correctly identified the asteroid by following a similar procedure on several more nights, during which the apparent movement of the asteroid amongst other stars similar to that shown on the Finder Chart shouldshout be apparent. There is great fun and satisfaction to be had from finding asteroids.

The next stage may result in making observations of scientific worth. Once correctly identified if the observer is able to make a series of observations of the asteroid over a period of many nights, employing the basic methods used by Variable Star Observers it is possible to assess the apparent brightness of the asteroid which will vary over a period of time and subsequently an interesting light curve graph can be produced. Various books such as in particular "Observing Variable Stars" by David Levy will be found helpful about the procedures, and the SPA Variable Star Section Director may provide advice if potential SPA observers ask him nicely and send an SAE.

Maintained by Michael Oates Email: mike@ph.u-net.com
Last modified 3rd Sept 1996