June Sky from the Keeble Observatory

Last month (May) we promised to keep you updated on the antenna problems experienced by the Mars Global Surveyor spacecraft. The news is actually pretty good. The gimbal on the high gain antenna is unable to rotate fully, limiting the orientations available for sending telemetry to Earth. Tests have suggested that a piece of insulation has frayed and is blocking the full motion. However, Mars and Earth are currently in a favorable alignment, so the range of antenna motion is sufficient to operate the spacecraft to its full capacity. Detailed surface mapping continues.

Meanwhile, two more Mars probes are half-way there! Mars Climate Orbiter, which will study the atmosphere of the Red Planet, was launched on 1998 December 11. It will arrive on the 23^rd of September, firing its braking rockets for capture into an elliptical orbit. The orbit will be lowered and circularized by a combination of thruster firings and aerobraking into a circular orbit with a period of about two hours. A few weeks after reaching its final orbit, the Climate Orbiter will be joined by the Mars Polar Lander. This vehicle was launched on the 3^rd of January, and is nominally on course for a December 3^rd landing near the Martian south pole. Also along for the ride are a couple of penetrating probes, known collectively as Deep Space 2. These will not be slowed by retro-rockets to a soft landing, rather they will slam into the surface to penetrate and analyze what is assumed to be ice or permafrost. The Climate Orbiter will serve as the radio relay link for the lander. Once the lander's batteries are dead, the Climate Orbiter will resume its detailed mapping mission for up to two years (one Mars year). Thereafter, if systems continue to operate properly, it should be available as a relay satellite for subsequent landers for up to two more years.

Lunar phases for June: Last Quarter at 12:20 am EDT on the 7^th; New Moon on the 13^th at 3:03 pm; First Quarter at 2:13 pm on the 20^th; Full Moon at 5:37 pm on the 28^th.

Venus is still the brightest "star" in the early evening sky, a bit north of west at dusk. It reaches it greatest elongation (angular separation from the Sun) on the 11^th. At mid-month it's midway between Regulus and Castor and Pollux in Gemini. Mercury is also visible, if you can get an unobstructed view to the northwest. It's below and to the right of Venus, setting very early at the beginning of the month. The regular rhythm of planetary motion will bring it closer in the sky to Venus as the month goes on. Early in June Venus will appear to form a straight line with Castor and Pollux, Mercury does the same later in the month. That bright red "star" to the south in the early evening is Mars, but don't confuse it with Antares, lower and more to the southeast. Jupiter and Saturn can be seen in the early morning sky, with Jupiter low in the east at dawn and Saturn a bit below and to the north of Jupiter.

An overhead view at 9:30 at mid-month looks out of the plane of our Galaxy. The Milky Way is just above the eastern horizon. Not quite at zenith is the bright star Arcturus, in Bootes. To the south, near Mars is Spica in Virgo, and to the west we see Regulus in Leo. Another triangle of bright stars runs from Arcturus to the southeast, where we find the bright red Antares in the constellation Scorpio, then to the northeast to blue-white Vega in Lyra. M51 - the "Whirlpool" - is a face-on spiral galaxy near the end of the handle of the Big Dipper. It's high to the north, and a good binocular target for the first half of the month, before competition from moonlight makes it harder to see. Another good binocular event is available on the 12^th, when Venus passes just north of the Beehive Cluster (M44). The cluster is hard to pick out this close to the horizon, but Venus will make finding it an easy task.