Gamma ray bursters have been an enigma since they were first discovered by spy satellites looking
for nuclear tests. These are brilliant, transient sources of gamma radiation (high energy light),
typically lasting only a few seconds, and scattered at random over the sky. Their distribution has
suggests that they are extremely distant, since nearby objects would be expected to concentrate in
the plane of the Galaxy. If they were in the "halo" of the Galaxy, we would expect to see them to
be fewer and fainter when looking towards the center of our Galaxy.
A detector on the Compton Gamma Ray Observatory (one of NASA's orbiting telescopes)
detected a strong burst on the 23rd of January, at the same time it was also seen by an Italian-Dutch satellite called Beppo-SAX. The NASA instrument signaled a computer at the Goddard
Space Flight Center in Greenbelt, Maryland, which automatically opened and pointed a remote
telescope in New Mexico towards the coordinates of the gamma burst. The time delay between
the observations was about 10 seconds, which is the average duration of a gamma ray burster!
For years, Goddard astronomer Scott Barthelmy had been trying this automated system to catch
an optical image of a gamma ray burst, only to catch the fading afterglow. Last January's event,
however, was caught at peak - the first time for such an observation.
Not only was this the first time, but it showed the burster to be extraordinarily distant and
powerful. Its distance is estimated at about 9 billion light years, about 2/3 of the way back to the
Big Bang (or 2/3 of the way to the observable "edge of the Universe"). It's power output would
have exceeded the energy released by a million galaxies, had it been radiated isotropically.
Theorists are now using the data from this burst to refine models attempting to explain the
phenomenon, and observers are also using it to argue for better and more reliable funding for the
automated telescope network which collected the data.
Lunar phases for April (All times Eastern Daylight): Last Quarter on the 8th, 10:51 pm; New
Moon on the 16th, 12:22 am; First Quarter on the 22nd, 3:01 pm; Full Moon on the 30th, 10:55 am.
That brilliant "star" to the west after sunset is the planet Venus, with Saturn not nearly as bright
beginning about 14 degrees below on the first, about a degree lower each night until it disappears
in evening twilight by mid-month. Saturn will be at "conjunction" (in the same direction as the
Sun) on the 27th. Mars returns to the evening skies, rising ESE in early evening, progressively
earlier as the month goes on. It will brighten spectacularly as Earth catches up in our separate
orbits around the Sun, going "retrograde" almost 10 degrees. (Mars was "stationary" on the 10th
of March.) Mars will be the brightest "star" in morning twilight to the southwest. Mercury is
barely visible above the eastern horizon as the Sun rises. Jupiter returns to the morning skies at
month's end, rising near Mercury on the 29th and 30th.
An overhead view at 9:00 pm at mid-month shows a very different sky from last month's. First,
it's not quite as dark, since we've shifted to Daylight Saving Time on the 4th - clocks moved
ahead one hour to give more early evening light, but making astronomy a later night activity!
Castor and Pollux are to the west of zenith, while bold Regulus is now almost due south.
Binoculars will help you find several interesting galaxies in Leo - consult a good finder chart to
optimize your search. To the south southwest we see Orion, making its final appearance for the
season, yielding the winter sky for spring. Sirius is the brilliant blue-white star above the
southwest horizon. Aldebaran, Elnath, and Capella vie with Venus for the western crown. Note
that most of the brighter stars are towards the west, since this is the direction into the plane of the
Regulus forms part of the "Summer Triangle" with Spica (southeast) and Arcturus (east). Relatively few bright stars to the east tells us that we are looking out of the galactic plane. Ursa Major is now high and inverted above the northern horizon. Binoculars or a small telescope reveal several distant galaxies and nearby binaries.