Half the planets have gone into hiding. Mercury is too low in the dawn sky for northern hemisphere skywatchers, and Mars, Venus and Uranus are gathered around the sun concealed by its glare. Only Jupiter and Saturn remain available for our viewing pleasure.
Still, it’s hard to keep planets hidden away when you’ve got the eyes of the Solar Heliospheric Observatory (SOHO) on your side. SOHO orbits around a stable region of space called the L1 Langrangian point where the gravity of Earth balances that of the sun.
From this prime observing spot, scientists use SOHO’s cameras to study the sun in many wavelengths or colors of light. Special devices called coronagraphs block the overly-bright solar disk with a metal stop to allow viewing of the sun’s outer atmosphere or corona. They also show other objects in the field of view like comets and the current gang of planets – Uranus, Venus and Mars.
Since the planets are very near one another, lots of interesting lineups will happen in the coming days. Venus reaches superior conjunction on March 28 (tomorrow) when it lines up on the opposite side of the sun from Earth. Six hours later it’s only one degree (two full moon diameters) below Uranus. An hour after, Uranus is in conjunction with the sun. Then on April 6-7 Venus and Mars will be in conjunction just half a degree apart. Is this beginning to sound like a barn dance?
One thing to remember about conjunctions – the planets involved are not physically close; they only appear to be because we see them in the same line of sight. If you’d like to watch all these interesting encounters, check out SOHO’s latest coronagraph image.
For us, Mars’ proximity to the sun is interesting but inconsequential. Not so for the Curiosity mission. On April 17 the planet is in conjunction on the opposite side of the sun from Earth. From our perspective, Mars will appear extremely close to the sun’s brilliant disk. Radiation from solar flares and high-speed subatomic particles in the sun’s corona can disrupt radio transmissions between the two planets during close alignments like this one. To prevent compromised radio commands from reaching either Curiosity or the older Opportunity rover, mission controllers will temporarily suspend transmissions from April 9 to 26.
Communications from Mars to Earth will also be reduced. To stay in touch, Curiosity will send daily beeps to Earth. Meanwhile both rovers and orbiting Mars satellites will continue science operations. Data gathered will be stored and then beamed to Earth in early May. The rovers’ spring break will be tame by earthly standards; both will stay put during the interval to prevent any shenanigans.
Did I mention there are still two great planets out at night? Jupiter stands high in the west-southwest at nightfall. It’s the brightest object in that direction. Saturn comes up later around 11 o’clock in the southeast about one extended fist to the lower right of Spica. The full moon will be near Spica tonight and Saturn on Thursday night. Much to see for all!