April 2002 Sky from Keeble Observatory
Just to catch up on various spacecraft: Last month's repair of Hubble Space Telescope (HST) was a spectacular success. Most trepidation centered on the replacement of the main power distribution controller. It had to be done, but it wasn't designed to be serviced in orbit! Worse still, the repair required shutting down all of HST's systems and hoping they would come back on without incident. Mission managers likened this to a heart transplant. All systems apparently powered up successfully, as controllers declared, "We have a heartbeat." Also replaced were the solar arrays. The new panels are smaller and more rigid (so should trigger less vibration as they expand and contract when moving from light to shadow, and vice versa), and are also about 20% more powerful.
The Near Infrared Camera and Multi Object Spectrometer (NICMOS) got a new, experimental cooling system. Infrared detectors have to be kept as close to absolute zero as possible, else they detect themselves! The original cooling system was a block of frozen nitrogen. However, the coolant developed a leak and sublimated (turned to gas) much faster than planned, leaving the NICMOS detectors useless. There's no guarantee of revival, but a new refrigeration system was installed, and flight controllers are working to bring NICMOS back on line.
The new Advanced Camera for Surveys (ACS) should begin returning images this month. Expect greater resolution and sensitivity than available with most of the Wide Field Planetary Camera (WFPC-II). Models suggest a 20-fold improvement, so expect a flurry of images which will be both spectacular and revealing of new phenomena.
Galileo is still on trajectory for a fiery dive into Jupiter's atmosphere in November. The spacecraft suffered additional radiation damage during its latest Io flyby, so was unable to return any images. The cameras have been turned off for the duration, leaving radiation and magnetic field detectors as the primary active systems. Overall, in six years at Jupiter, the probe has survived over four times its designed radiation limits. Not bad!
Mars Odyssey has begun returning data from its orbital vantage. This probe is mapping the Martian surface with infrared cameras and remote radiation sensing. Its primary mission is to assess the surface composition and to look for evidence of water beneath that surface. Preliminary results are consistent with substantial water, probably in the form of "permafrost" beneath the Martian soil, extending from the south pole to about 60 degrees latitude. Similar data are not yet available for the northern hemisphere, which is going through Martian winter. Frozen carbon dioxide (dry ice) on the surface masks any evidence for subsurface water. Northern hemisphere summer is coming, so controllers are waiting before beginning that part of their measurements.
Lunar phases for April: Last Quarter on the 4th, at 10:29 EST; New Moon on the 12th, at 3:21 EDT; First Quarter on the 20th, at 8:48 EDT; Full Moon on the 26th, at 11:00 pm.
Planet watchers will have to content themselves with evening viewing - none are visible in the morning skies this month! Venus is brilliant, setting towards the West about 2 hours after sunset by the 21st, shortly after the end of twilight at the beginning of the month. Jupiter starts the month about 60 degrees around the sky from Venus, high to the south. By month's end, Jupiter trails Venus by only 34 degrees. Saturn can be found between Venus and Jupiter all month. Mars is between Saturn and Venus! Mercury emerges from the solar glare at midmonth. Look for this second "evening star" below and to the right of Venus, climbing higher and brighter by the end of the month. All five of these planets will be visible at the same time this month!
Our overhead view at mid-month, about 8:30 pm daylight time (we "spring ahead" on the 7th) finds the Twins of Castor and Pollux just to the west of zenith. The Milky Way stretches north to south, but arches to the west. The plane of the Galaxy cuts below Gemini, just above Betelgeuse in Orion. Prepare to bid farewell to this most familiar winter constellation - the Vernal Equinox arrived last month, heralding the arrival of Spring. Saturn is still near Aldebaran, in Taurus. To the southwest we see Sirius, brightest star other than the Sun visible from Earth. This brilliant star is also known to have a collapsed white dwarf companion orbiting it, but "Sirius B" is not visible without a large telescope. Ursa Major is high above the northeast horizon. The bowl of the "dipper" is inverted toward the north-northeast horizon. The "handle" forms a lazy arc that bends back and to the east. If you follow that arc, you will find Arcturus, the brightest star in the constellation Bootes almost due east. High to the southwest is Leo, marked by the bright star Regulus. The sky from zenith to the east provides a rich binocular view out of the plane of the Galaxy. It is here that you can find numerous external galaxies, and several globular clusters orbiting our own Galaxy. The sky to the west of zenith is rich in star fields and clusters within the Milky Way itself.
George F. Spagna, Jr.