Venus appears in the southwestern sky at dusk, while the pair of Jupiter and Saturn rule the roost at nightfall in the southeast. Mercury is currently invisible in the sun's glare but will return for a fine appearance at dawn later this month. That leaves Mars. Where the heck is the Red Planet?
You'll need to use your imagination because it's nearly aligned with the sun in the sky and completely submerged in its glare. From Earth that is. The NASA / ESA solar probe SOHO (Solar and Heliospheric Observatory) can still picture Mars from orbit by using a special occulting disk to block the sun's blinding light.
Mars lies nearly in the same line of sight as the sun but on the opposite side of its orbit from Earth, so it's really, really far away. On October 3rd, 245 million miles (394 million km) separate the two planets. Exactly the opposite situation occurs when the Earth and Mars are paired up on the same side of the sun. Then they can be as close as 34 million miles (55 million km) apart.
Mars sits just a pinky to the sun's upper left today. They'll be closest when the planet is in conjunction with the sun on Friday, October 8th — less than one sun-diameter apart!
NASA has to take special precautions around the time of conjunction. Data sent by rovers and orbiting spacecraft at Mars must pass through clouds of charged particles (solar wind, flares, etc.) near the sun on its way to the Earth. This could lead to corrupted or missing information. Worse, a command sent from Earth might be garbled after passing close to the sun and cause a rover to misfire or lock up. That's why the agency suspends science operations for several weeks during the once-every-1.9-year alignment.
Not surprisingly, Earth also appears close to the sun for an observer on Mars since the two planets and sun lie along a nearly straight line. From Mars, Earth is one of the inner planets along with Venus and Mercury. Recall that the inner planets swing out a short distance on either side of the sun. They can't get back "behind" the Earth like an outer planet, so it's impossible for them to appear opposite the sun in the midnight sky. Instead they cycle back and forth from evening twilight to morning twilight, the reason they're nicknamed the "evening" and "morning" stars.
An inner planet also shows phases like the moon as the angle between it, the sun and the observer changes as the planet plies its orbit (see above). Future astronauts on Mars will see Earth as an evening or morning star and watch it change phase from crescent to half to full. Very nice! Except they better bring a small telescope.
Viewed from millions of miles away, Earth is puny. At largest, when it's a crescent and closest to Mars, you'd be able to make out its shape in 10x binoculars. The smaller, fainter moon would appear as a dim, 4th magnitude companion "star" (also a crescent) one-third of a degree away and too small to reveal a phase.
Because the Earth is so much brighter than the moon I suspect it would difficult to see them as a pair with the naked eye at that time — perhaps averted vision would do the trick. But binoculars would separate them clearly then and any other time.
Over the coming week, the sun will slowly pass Mars by, and the planet will cross over into the morning sky. As the sun keeps moving east (caused by Earth's orbital motion) Mars will gradually emerge from the dawn glow and return to view by mid-late November. Meanwhile, for our Martian astronauts, the Earth slowly departs the solar glare and moves into the evening sky. It reaches its greatest apparent distance from the sun (46°) next July and set late in the evening.
That would probably be the best time to see both the Earth and moon together as a "double planet" without optical aid. They'll both relatively close to Mars then, with the moon showing enough of a phase (around half, with a magnitude of 2) to compete against Earth's glare. They'll also be about 1/4° apart, similar to the separation between Jupiter and Saturn at the their Great Conjunction in 2020.
All the planets orbit the sun in a relatively flat plane, so no matter which one you visit, you'll always find the others along the same "plane" in the night sky called the ecliptic. Go to Mars, and the Earth cycles through the same zodiac groups as Mars does here on Earth. Once you identify our planet by its radiance and distinctive blue hue, you'll be able track it across the same 12 constellations from Mars.
Sometimes it's hard to appreciate that Earth is just one planet among many and "lives" in the sky just like the others.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.