The M.A.S. Newsletter

Journal of the Mauritius Astronomical Society

February 2001 (Memo)

The Next Meeting:

Please take note of the following information which has been omitted in the last newsletter:
The Annual General Meeting will be held at Collège du Saint Esprit, Quatre Bornes on Friday 23rd February at 19:30.

Agenda:

  1. Reading and approval of previous minutes
  2. Matters arising
  3. President’s address
  4. Treasurer’s report
  5. Committee members for 2001
  6. AOB

Members wishing to form part of the committee should send their letters to reach the Secretary not later than Thursday the 22nd of February.

My address:

S. Florens,
47 Rue Vengta,
Solferino.

We hope to see you for this important meeting.


Name of Stars in Orion:

The map opposite shows the constellation of Orion (the Hunter) with the proper name of the brightest stars. This constellation straddles the celestial equator and is close to the zenith at about 21:00. To view the constellation as represented in the map, lie down head towards the north. Three bright stars mark his belt (Alnilam, Alnitak and Minkata) and several fainter ones a sword hanging from it. Orion contains five stars of the first magnitude or brighter and a further ten brighter than fourth magnitude. The most spectacular diffuse nebula in the sky, the Orion nebula (or M 42) is faintly visible to the unaided eye in the 'sword'. This is the birthplace of stars and is found at about 1 500 l.y.

Orion


Some More Astronomical Terms:

Doppler Effect: In astronomy refers to the change in the observed frequency of electromagnetic waves (gamma rays, X-rays, ultraviolet, visible light, infrared, radio waves, etc) when the source and waves are moving towards or away from each other. This effect is observed in the light from an astronomical object, features in the spectra of which can be shifted towards longer or shorter wavelengths according to whether the source is receding from or approaching the observer respectively.

Redshift: The fractional increase in wavelength of electromagnetic radiation caused either by the Doppler effect, when the source of radiation is moving away from the observer, by the presence of a gravitational field or the expansion of space. It is expressed as the ratio of the wavelength change D l to the rest wavelength l (when the source and observer are not in relative motion): z = D l / l . A redshift caused by the expansion of the Universe is properly called a cosmological redshift to distinguish it from a Doppler shift. Doppler shifts are caused by a source's motion through space, whereas a cosmological redshift is caused by the expansion of space.

Hubble's Law: The recessional velocities (velocity away from us) of distant galaxies are directly proportional to their distance from us. It is a consequence of the uniform expansion of space. The relationship was discovered from observations of the cosmological redshifts of galaxies and was first announced by Edwin Hubble in 1929.

Serge Florens, Secretary