Starry Skies Above Santa Monica

February 21-28, 2001

Mirek Plavec
Emeritus Professor of Astronomy, 
UCLA

   Sun, Moon and Planets
   The Sun is traveling upward through Aquarius (the Water Bearer), and is now only 9 degrees below the equator. On Sunday, February 25, it will pass, at the local noon, very close to the zenith of the island Ascension, over Surabaya, Java, and over Recife, Brazil. For us, the Sun will rise at 6:26 (a gain of 8 minutes per week) and set at 5:46 p.m. (6 minutes later than a week ago) – so, again, a net gain of 14 minutes of daylight time.
   On the morning of February 21, you might glimpse the Moon as a very thin waning crescent, barely visible before sunrise. On that morning, the Moon will be passing below the planet Mercury, which is, however, rather faint this time. The Moon will then disappear completely, since it becomes "New" on the night of February 22/23, passing below the disk of the Sun. After that, the Moon will reappear very soon as a thin crescent in the western sky. You may probably glimpse it already, soon after sunset, on the evening of Sunday, February 25. It will then be well below the brilliant Venus. On the next evening, Monday, the Moon will be already at the same height above the horizon as Venus, but will lie fairly far to the south of the planet. On the evening of Wednesday, February 28, the crescent Moon will form a nice trio with Saturn and Jupiter, much higher above the western horizon.
   Venus, in Pisces, reaches its greatest brilliancy (astronomically speaking, its magnitude will be -4.6) on February 21. Venus is still very prominent every evening, visible fairly high above the western horizon already by 6:10 p.m. or so. It shines quite long, and sets by 8:50 p.m. If you compare the time of setting with the previous Sunday, you will notice that Venus sets 10 minutes earlier than last Sunday, while the Sun sets 6 minutes later. The fact that Venus is returning to the Sun (as seen in our sky, i.e. diminishing its angular deviation eastward of the Sun) is beginning to show, but Venus still remains prominent and fairly high in the sky shortly after sunset.
   When the sky gets still a bit darker, you will have no problem in finding the bright Jupiter so high in the sky that you will think that it is "nearly overhead." Saturn, fainter (but still first-magnitude "star") is not far to the west of Jupiter. The two planets are now visible above the south-west, but high up in the sky Both planets now move eastward among the stars, but at a snail’s speed, so you will find them pretty much at the same place where they have been for weeks. Currently, they are fairly close to each other, Jupiter still between the Pleiades and Aldebaran, and Saturn not far from Jupiter, a few degrees to the west. It is the motion of the Earth, as reflected in the apparent motion of the Sun, that changes their visibility: around midnight, they set in the west. 

   Commemorating a Famous Supernova
   One of the most important events of contemporary history occurred on February 23, 1987: Canadian astronomer Ian Shelton discovered a supernova in the Large Magellanic Cloud, which is a nearby "satellite" galaxy to our own majestic "Milky Way" Galaxy.
   Why was it such a memorable event? Supernovae are tremendous cosmic explosions, in which a star almost destroys itself, throws most if its stuff into space, and the remnant collapses into a tiny neutron star or a black hole. Do you think that such a remote event is of no interest to you? Well, without it, you and I would not be here! The stars you see shining in the sky consist mostly of hydrogen and helium – important stuff, but definitely not enough to build our bodies! Heavier elements, up to iron, are synthesized deep in the interior of supergiant stars, such as Beteigeuze in Orion or Antares in Scorpion. To produce something is just one step: you must transport it out of the factory, and make it available to the outside world. The supergiants are slow in this respect: mixing inside their bodies transports the heavy elements into the atmosphere, and stellar wind disperses them around the star. 
   A good supernova is much more efficient! Within hours and days, it throws the material into space at high speed. And, ladies, it is only during the supernova explosion that the gold and silver in your jewels are created! Think kindly of supernovae!
   Astronomers have long desired to see a nearby supernova, in order to study the event with modern techniques. However, nearby supernovae are rare. The last two really good ones that exploded in our Galaxy did so in 1572 and 1604 – before astronomers started to use telescopes, let alone more modern instruments such as spectroscopes!
   Thus, the supernova of 1987, although some 170,000 light years distant, was a real gift! Special surveys detect supernovae fairly often – but always in faraway galaxies, so they remain faint even at maximum luminosity. For the first time ever, it was possible to find the predecessor of the supernova, since the same region had been carefully photographed by Shelton and others. The star that eventually exploded was a blue supergiant with an original mass of about 20 solar masses. Thanks to it, we now know much more about those gigantic cosmic explosions.