Starry Skies Above Santa Monica

May 22-29, 2002

Mirek Plavec
Emeritus Professor of Astronomy,
UCLA

   Long Sunny Days, Bright Nights
   This is, in short, the astronomical picture of the coming week. On Sunday, May 26, the Sun will rise at 5:45 a.m., culminate at 12:50 p.m. (remember, we have the daylight saving time), and set by 7:55 p.m. Thus we are entitled to 14 hours and 10 minutes of sunshine.
   And when the Sun eventually sets, the Moon will take over. On the first four evenings, the Moon will be above the horizon already at the time of sunset -– search for it in the southeast, it will show you almost its entire bright face. The actual Full Moon comes in the morning of Sunday, May 26. After that, the Moon’s illuminated face will slowly decrease, and the Moon will gradually rise later, every subsequent night by about one hour. Thus, on Wednesday, May 29, the Moon will rise only 30 minutes before midnight.
   As the Moon travels eastward with respect to the stars, it will pass by Spica, the first-magnitude star in Virgo, between Wednesday, May 22, and Thursday. Then it will move through Libra into Scorpius, and on Sunday evening, it may help you to identify the reddish supergiant star Antares. Then it will pass through Sagittarius into Capricorn.

   Evening Planets: Only Two Are Left
   Definitely gone is Mercury, which will be in the inferior conjunction with the Sun on May 27, meaning that Mercury is projected in the direction to the Sun; “inferior” means that the planet is located between us and the Sun – thus is it actually closest to the Earth, but lost in the glare of the Sun.
   Practically lost will be Saturn, which sets already by 8:42 p.m., less than one hour after sunset, and although it shines as a star of the first magnitude, it will be lost in the bright sky above the west.
   No better is the situation with Mars. It is projected farther from the Sun, and sets one hour after Saturn, but it is fainter, of the second magnitude, so it will probably be lost, too.
   So only two planets are left to adorn our evening sky: Venus and Jupiter. Both are projected into the constellation of Gemini, but Jupiter is farther to the east, and sets a few minutes before 11 p.m. Thus it can still be seen in the western sky when it gets a bit darker, say about 9 p.m. Jupiter is sufficiently bright to be recognized without difficulty.
   However, the ruling planet is Venus. It comes into view at about 8:30 andsets by 10:30, so for two hours, it clearly dominates the western sky, being significantly brighter than Jupiter. Venus is moving faster eastward among the stars, and will catch up with Jupiter soon. Thus, on June 3, and for a number of evenings around this date, we will see Venus and Jupiter as a brilliant pair of bright objects in our western sky.

   Rich – and Richer
   No, I did not cast a horoscope to predict the progress of U.S. economy, nor am I going to talk about Beverly Hills and the like, neither am I persuading you to gamble in Las Vegas. I want to stick strictly to my duty, to tell you something new about the universe.
   And there is something new: an original attempt to determine the age of the universe! Until now, such estimates have been based on our limited knowledge about the expansion of the universe. We know that the distant galaxies are all moving away from us, and the fainter the galaxies appear to us, the greater is their speed. This led to the concept of Big Bang, after which the universe started to expand. Our clear difficulty is to understand how the speed of expansion changed over the ages.
   The new clue to the age of the universe lies much closer to us, actually well inside our Galaxy, only 6,000 light years away! It is a globular cluster known as M4 (its full name would be “Messier 4,” as it is the fourth object listed in the famous catalog compiled by Charles Messier in France in 1781). This cluster is fairly bright, and when it comes higher up in the evening sky, I will tell you how easy it is to find it, even with binoculars.
   However, the important study I am talking about here is based on a careful search for the very faintest stars in this rich cluster -- the white dwarfs. And they are truly faint! It was necessary to use the Hubble Space Telescope for 120 its orbits around the Earth, in order to detect those tiny stars.
   Why such tremendous effort, and such a large block of time with that precious telescope? The evolution of stars is well understood, and the recent modeling of white dwarfs by the UCLA astronomer Brad Hansen made it possible to determine reliably the ages of the white dwarfs inside the M4 globular cluster. The actual observations were performed by a team led by the Canadian astronomer Harvey Richer and the UCLA astronomer Michael Rich.
   Their result? These ancient white dwarfs have been found to be 12 to 13 billion years old. And previous studies showed that such stars probably formed within one billion years after the Big Bang. Thus the conclusion is that the universe is approximately 14 billion years old. What impresses me is not this number, but the sophisticated and careful effort to exploit fully the great opportunity offered by the Hubble Space Telescope, and the truly innovative modeling of the structure and evolution of those tiny stars.