Tonight – January 12, 2014 – cast your mind outward in space toward the Pioneer 10 spacecraft, one of the most distant spacecraft from Earth at this time. Pioneer 10 was launched from Earth on March 3, 1972. It was the most distant humanmade object from Earth until Voyager 1 overtook it – at 69 Earth-sun distance units, or AU – in 1998. On January 12, 2014, both the moon and Pioneer 10 reside in the direction of the constellation Taurus the Bull. You can’t see it (and it can’t see Earth), but you can imagine it tonight.
Tonight’s moon will be a waxing gibbous moon, though it’ll be so big and bright that you might think it’s full. The giant planet Jupiter is the brightest object near tonight’s moon; the moon will be moving closer to Jupiter in the coming days. The moon’s brilliance will erase many stars from the sky, but you still should be able to make out the Taurus’ stars Aldebaran and Elnath. The Pioneer spacecraft resides between these two stars on the sky’s dome.
Of course, when we say that the moon is near Pioneer 10 tonight, what we really mean to say is that the moon and Pioneer 10 are close together on the sky’s dome. In actuality, the moon and the Pioneer 10 spacecraft are nowhere close together in space. They’re simply located near each other along our line of sight.
The moon lies just over one light-second from Earth, while Pioneer 10 lodges way out in the far reaches of the solar ssytem at over 15 light-hours away. At present, Pioneer 10 is traveling about one light-hour farther away from the sun every 3 years. That doesn’t sound like much, but remember that light travels at a speed of 300,000 kilometers (186,000 miles) per second.
Pioneer 10 passed closest to Jupiter in space on December 4, 1973. It passed the orbit of Pluto on June 13, 1983. This spacecraft is now nearing or at the outer boundary of our solar system. In the not-too-distant future, Pioneer 10 will enter the realm of interstellar space. We won’t know when that happens, however, because this spacecraft no longer sends data back to Earth.
Although the moon will leave the constellation Taurus in a few days, you can continue to envision Pioneer 10 – with the mind’s eye – in between Taurus’ two brightest stars, Aldebaran and Elnath … for some time to come.
Bottom line: Use the moon on January 12, 2014 to imagine the whereabouts of the Pioneer 10 spacecraft, now leaving our solar system. As seen on Earth’s sky dome, Pioneer 10 is in front of the constellation Taurus the Bull.