Dark matter and dark energy add to mystery of the cosmos

By Clair Wood, Special to the BDN
Posted April 05, 2011, at 9:26 p.m.

When you gaze skyward on a dark clear night and see the almost countless number of stars and galaxies shining there, you would be forgiven for thinking you are looking at the grandeur of the entire universe. Not even close.

Cosmologists say that 23 percent of the universe is made up of dark matter, 73 percent is dark energy, and only 4 percent is luminous matter that makes up the stars, galaxies and you and me.

Dark matter, whose true nature is unknown, neither absorbs nor emits light and can be inferred only from studies of stellar motions that show the gravitational mass of galaxies is more than 10 times the luminous mass. Dark energy, whose nature is only guessed at, is a force that counteracts ordinary gravity and is causing the universe to expand at an increasing rate.

Any experimental proof for the nature of either dark matter or energy would be an almost certain guarantee of a Nobel Prize in physics but, for now, we can only speculate about these enigmas of the mysterious universe.

Focus on the Planets

April will see a gathering of six planets in the predawn sky as the month draws to an end while Saturn is the only planet to grace the evening sky.

Mercury rises very low in the east just before sunrise near month’s end, but will be hard to spot even with binoculars.

Venus rises in the east about an hour and a half before dawn as April opens and is the brightest point of light in the morning sky. On April 1 the thin crescent moon lies just to the left of Venus.

Mars lies low in the east in close proximity to Jupiter as the month winds down, however, it may be too faint to be seen even with the aid of binoculars.

Jupiter is the only one of the triumvirate of planets in the eastern predawn sky that will be readily visible by binoculars at month’s end. Do not expect to see anything of note for details however.

Saturn may be found in the southeast at dusk. The ringed planet is the brightest it has been in three years and, with the opening of the ring system near maximum, will afford excellent viewing by telescope.

Uranus lies directly above Venus on the morning of April 23, but likely will be too faint to spot even by telescope.

Neptune can be found with the aid of a telescope in the southeast before dawn and will afford much better viewing as spring continues on its path.

April Events

1: Sunrise, 6:17 a.m.; sunset, 7:02 p.m.

2: The moon is at apogee or farthest distance from Earth.

3: New moon, 10:32 a.m. Saturn rises around sunset and remains in view all night long. Look to the southeast where Saturn shines like a golden star.

11: Moon in first quarter, 8:05 a.m.

16: Moon, Saturn and the bright star Spica for a triangle in the southeast an hour after sunset.

17: Moon is at perigee or closest approach to Earth.

18: Full moon, 10:43 p.m. The full moon of April is known as the Pink Moon or Egg Moon, and is also the Paschal Moon, the first full moon after the spring equinox.

19: Looking to the east just before dawn will reveal Venus to the naked eye while far below, Mercury and Mars are less than a degree apart, but will require a telescope to spot. Sun enters the Aries on the ecliptic.

20: Sun enters the astrological sign of Taurus, although astronomically it has just entered Aries.

22: The peak night for the Lyrid meteor shower which usually yields about 20 meteors per hour, but a bright gibbous moon will wash out all but a handful of the brightest in the predawn hours.

24: Easter. Historically, the date of Easter is calculated as being the first Sunday after the first full moon on or after the date of the spring equinox.

25: Moon in last quarter, 10:46 p.m.

29: Moon is at apogee for the second time in April.

30: Sunrise, 5:27 a.m.; sunset, 7:39 p.m. Look to the east just before dawn over the next few days for Venus with Mars, Mercury, and Jupiter just below.

Send astronomical queries to Clair Wood at cgmewood@aol.com or care of the Bangor Daily News, Style Desk, P.O. Box 1329, Bangor 04402.

http://bangordailynews.com/2011/04/05/living/dark-matter-and-dark-energy-add-to-mystery-of-the-cosmos/ printed on September 16, 2014