Jupiter Favourably Placed In March

Press, Volume CIX, Issue 32234, 28 February 1970, Page 8

Jupiter Favourably Placed In March

Of the five bright planets only Jupiter can be viewed under favourable conditions March. Both Mercury and Venus will be too dose to the Sun to afford more than a very brief glimpse during morning and evening twilight respectively.

it Mars and Saturn will •- be visible low in the north western sky for a short time after the end- ; ing of twilight in the j* evenings. Mars sets on March 1 at 8.45 p.m., on March 15 at • 8.20 p.m. and on March 31 i- at 7.45 p.m. Saturn sets at 9.20 p.m. on March 1; at 8.30 : p.m. on March 15 and at 7.30 p.m. on March 31. If readers ' wish to locate them a good : time to look is on the even- . ing of March 17. At 8 p.m. the two planets will be sepI arated from each other by - three degrees and will be very ■ close to the north-western t horizon at the time. Both these planets are now too low • for satisfactory viewing with telescopes. • Jupiter has become a brilliant object during the past i month and has attracted a lot of attention. It can be found in the constellation Virgo, close to its boundary with Libra. There the planet ' far outshines any of the surrounding stars. On March 1 Jupiter rises at 9.20 p.m., on March 15 at 8.30 p.m. and on March 31 at 7.15 p.m. During March there will be a total eclipse of the Sun • which, if the weather is fine, will be seen by huge crowds. The track of totality crosses Mexico where the longest duration of 3min 28sec occurs. It then swings northwards across Florida and the extreme eastern parts of the United States and Canada. Expeditions are going to many different localities but Florida will be the area that will attract the majority of laymen. This eclipse is not visible from New Zealand. New Star Discovered During February a nova, or new star, was discovered by . Honda, a Japanese astrono- ■ mer. It is located in the con- • stellation of Serpens, visible ; in the morning sky. The new < object lies almost halfway , from the bright star Gamma , Ophiuchi to Delta Aquilae, j This is a region of the Milky Way in which many novae , have been discovered of , which the most notable was i the brilliant Nova in Aquila j in 1918. , At discovery on February ■ 15 the new discovery was just , visible to the naked eye, i being of fifth magnitude i Observations made in New l Zealand since then have i shown that the star has i brightened to fourth magni- i tude. At the time these notes I were written the maximum I had not been reached. 1 Three Bright Comets ] So far this year there have 1 been three bright comets ! visible, two of which were 1 discovered last year. The 1 third of these was the first 1 comet to be discovered this year. It is called comet Daido-Fujikawa. It passed very close to the Sun during February and at that time 1 was much brighter than the brightest stars. It was then 1 only three degrees from the Sun and it required special instruments to see the nucleus. Comet Bennett during March moves very rapidly northward. It is predicted to reach its maximum brightness on March 25 when it should be equal to a second magnitude star. On that date it will be about four million eight hundred thousand miles from the Sun. It will then be in the constellation Aquarius and it may be possible to see the comet against the bright dawn sky just before sunrise.

The third bright comet, Tago-Sato-Kosaka, has now

faded and moved far north so that it is no longer visible from our latitudes.

1 Like so many discoveries • in astronomy, that of quasars > was an accident. It was made in 1960. Up to that time all known radio sources were j diffuse, each being spread t over a small area of the sky. L When such sources lie close t to the ecliptic it can happen I that the Moon will pass in j front of them in just the . same manner as it occults a I star. Since such radio sources , are spread over an area of the sky there is a marked ; difference between the occul- , tation of a star and a diffuse , radio source. In the former case the star disappears immediately, whereas the ' diffuse radio source is gradually covered by the Moon and therefore there is a gradual decrease in the radio ' noise received. ' It. was in 1960, when ‘ occultation of known diffuse 1 radio sources were being J observed from Jodrell Bank, that it was found that the intensity of one particular source suddenly dropped to zero. This showed that the origin of the radio energy for this particular source must be a star-like point. Because the position of the Moon’s limb is accurately known it was then possible to determine the position of this radio point source. It was not long before other point sources were discovered. They were given the name of quasi-stellar radio sources, which soon became shortened to quasars. Tracing Source It was one thing to make these discoveries but it was much more difficult to identify them with known optical objects. It was presumed that such objects must be identical with certain stars. So the region immediately surrounding each position was carefully examined for an unusual star, or other optical objects. This was done at Mount Palomar by securing spectrograms of all I likely stars and galaxies. 1 Examining these spectro- 1 grams A. R. Sandage found ' one of an object in which the emission lines could not '■ be identified with any known ' chemical element. Other spectra of known quasars ‘ gave the same result until M. Schmidt suggested that the spectra had been shifted' far to the red. He contended that the spectral lines were, in fact, due to known elements, particularly hydrogen, but they had been displaced by enormous redshifts. The redshift is a displacement of the spectral lines towards the red end of the spectrum due to an effect of velocity. If the originating source is moving away from us the amount of this dis- i placement is a measure of the velocity of recession. Very Distant Objects The extremely large redshifts of quasars implied that they were very distant objects. This meant that they represented the most distant'

objects known. This also implied , that they must be extremely bright objects to be detected at all. Mean while Schmidt had proved that one .of these quasars was identical with a compact blue galaxy, an object which optically was a star-like point and whose spectrum resembled that of known radio galaxies. At the tremendous distance involved this object optically outshone the normal spiral galaxy 100 fold. In 1965 Sandage showed that besides quasars there also existed a large number of quasi-stellar galaxies, shortened to QSG. These differed little optically from quasars but they had an absence of the strong radio emission that was present in quasars. It, was found that quasars are much rarer than QSG and also than normal galaxies. Current theories concerning exactly what a quasar represents are by no means proved. The puzzle is as to whether they represent objects that are being continually formed anew or are they some relatively short lived transition stage in the evolution of galaxies. Of course nobody knows exactly what a young galaxy or a transition object should look like. But it is reasonable to assume that both types would be very young and therefore should contain a large number of extremely hot, massive young stars. This could account for their tremendous brightness. Whatever the final answer will be as to the nature and origin of quasars, observations of them are actually not of something that is taking place in our time but of events that occurred as long ago as five thousand million years. It has taken that time for the light from them to reach us. Observations of such remote time provide a picture of a Universe with a high degree of uniformity without any clear indication of large scale changes in the past five thousand million years. If we picture the present speeds of recession being reversed we can consider that at something like ten thousand million years ago there was the initial concentration of matter which forms the Universe.