SKY REPORTER: Planetary Dances

If you’ve never had the pleasure of pointing out and identifying bright planets, or don’t remember where they currently are in the sky, this month the Moon again provides some fine opportunities for spotting Mars, Venus, and Jupiter. I enjoy thinking about planetary explorations while looking at those distant worlds. Venus and Mars now appear in twilight above our western horizon about a half hour after sunset and remain visible for several hours. Venus is always eye-catching, and binoculars are a help when looking for Mars.

Peaks and plates on the icy surface of Jupiter’s moon Europa.
Credit: NASA/JPL

Apparent separation between these planets is gradually increasing as days pass but the distance is no more than 17 degrees of arc (about one and a half fist lengths seen at arm’s length) at month’s end.

I’m looking forward to the evening of March 21. If the western sky is clear we might glimpse the delicate lunar crescent, just 38 hours after New Moon, positioned about one degree of arc (two Moon diameters) to the lower left of the Red Planet. At 7:40 p.m. that night, look halfway between Venus and the west point on the horizon for the Moon and Mars. If your western view is unobstructed watch them descend until moonset at 8:57 p.m. That evening Mars is 216 million miles from Earth, nearly 1,000 times further from our eyes than the Moon. The next night a wider crescent Moon is near the direction of Venus, a lovely configuration certainly worth a glance.

While considering Mars, we remember the short circuit that temporarily shut down operation of a vital drill assembly on NASA's Curiosity Mars rover earlier this month. The mechanism is now back in service on slopes of Mount Sharp investigating ancient Martian rocks for evidence the planet may have been habitable in the distant past. It’s also collecting data regarding long-term changes in the Martian environment.

Jupiter’s turn to be highlighted by a proximate lunar passage will be on the nights of March 29 and 30 when the waxing gibbous Moon may be seen less than 10 degrees of arc south of the big planet. On March 12, NASA announced evidence of a vast salty ocean with more water than all the seas of Earth, beneath a 95 mile thick ice crust on Jupiter’s moon Ganymede. It’s the Solar System’s largest satellite—wider than the planet Mercury and three and a half times more capacious than Earth’s Moon. For years there has been fascination with the notion of an ice covered ocean believed to exist on Europa, another of the four Jovian Moons discovered by Galileo. There also had been speculation Ganymede might have an even larger ocean. Apparent confirmation comes from innovative use of the venerable Hubble Space Telescope, now in final years of its 25 year run of historic space discoveries. A research team headed by Joachim Saur of the University of Cologne studied ultraviolet Hubble images, noting systematic rocking of aurorae lights surrounding Ganymede consistent with tell-tale interactions between Jupiter’s powerful magnetic field, a secondary field it induces in Ganymede’s presumed salty ocean, and the satellite’s primary magnetic field emanating from that moon’s liquid iron core.  

Water is an essential factor in a great quest of modern space research—finding the Holy Grail of life beyond our world. If life could evolve from inorganic materials in Earth’s primal oceans, might it also have evolved in seas such as we find on Ganymede and Europa? Alternatively, might life have arrived in the Solar System as intrepid spores, deep space travelers from some distant stellar realm, originating eons before the Sun and its family formed 4.5 billion years ago? Europa’s surface shows features on its icy crust raising the possibility that small amounts of liquid water might at times reach the surface, thereby allowing a future space craft to test it for evidence of life, without need of penetrating many miles of ice before sampling that moon’s ocean.

On the evening of March 29, the Jovian moons Callisto, Ganymede, and Io will be in line east of Jupiter’s disk with Io nearest the planet. Europa will then be west of Jupiter. A telescope providing at least 20 magnifications, held in a firm mounting, should easily show these fascinating worlds. Early the next night Calisto and Ganymede will be nearer each other east of the planet, and Io will have orbited to the western side of Jupiter. Europa will be behind the planet hidden from our view until just before nine p.m. when it moves into sight past Jupiter’s eastern edge.

The Moon

Planets

This month Venus, Mars, Jupiter, and Uranus are all located in our evening skies. Saturn rises around midnight but we wait until shortly before dawn before Mercury and Neptune arrive over the eastern horizon.

Spring begins in the northern hemisphere at 6:45 p.m. EDT on the evening of March 20. At that time the Sun is located above a point on the equator in the Pacific Ocean 1,325 miles South by West from the Big Island of Hawaii.

On the evening of March 21, the narrow crescent Moon is just to the left of Mars in the southwest during early evening. The next night the lunar crescent is to the left of bright Venus.

On March 29 and 30, the waxing gibbous Moon is near Jupiter.

On the 31st at 8 p.m., in fading twilight 40 minutes after sunset, Mars will be about ten degrees above the horizon and 17 degrees beneath Venus.