Close Encounters with Mars
Close Encounters with Mars Everyone on Earth will be close to Mars this week,
but the people of French Polynesia will be closest of all.
August 25, 2003: At 09:51 universal time (UT) on August 27th, Earth makes its closest approach to Mars in nearly 60,000 years. The two worlds, center-to-center, will be just 56 million kilometers apart--a short distance on the scale of the solar system. The last people to come so close to Mars were Neanderthals.
Right: An artist's rendition of Mars in the night sky 60,000 years ago. [more]
Magazine articles, newspapers, and TV shows have touted the encounter for months. But they all omitted one detail: Which part of Earth?
Think about it: At the moment of closest approach one side of our planet will be closer to Mars than the other. Earth is about 12,756 km wide, so the difference--one side vs. the other--is trifling compared to the vast distance between the two worlds. But the fact remains that someone, somewhere will be the closest ever to Mars. Where?
The answer is Tahiti.
While Tahiti is facing toward the red planet, another spot on Earth diametrically opposite will be facing away: the Nubian Desert of Sudan. This is the place on Earth farthest from Mars.
Everyone on Earth will have a close encounter with Mars this Wednesday. Your personal encounter happens when Earth's rotation carries your hometown across the Mars-facing side of our planet. None of these encounters will be as close as the Tahitians'--but they're all good.
The table below lists moments of closest approach for selected cities around the world. New York City, for instance, will be nearest to Mars at approximately 05:46 UT (1:46 EDT) on August 27th. The last column (DTahiti) is a comparison to Tahiti. People living in Tahiti will get 3172 km closer to Mars on August 27th than people living in New York.
Table notes: (1) Approximate times and distances were calculated using JPL HORIZONS. (2) DTahiti compares the minimum distance to Mars from the listed city to that of Tahiti. For example: people living in Tahiti will get 55 km closer to Mars than people living in Samoa. (3) UT is universal time. (4) Local time means the time on clocks in the tabulated city.
A good rule of thumb: If you want to see Mars when it's closest to your hometown, be outside around 1 o'clock Wednesday morning. Look south and up. Contrary to some reports, Mars will not be as big as the full moon nor will it cast shadows. But it will be bright (magnitude -2.8) and beautiful--like an intense butterscotch-colored star. You can see it even from brightly-lit cities.
There will be lots of "Mars parties" organized this week to celebrate the moment of closest approach. Here in North America, the best times to do that are Tuesday evening (Aug. 26) and Wednesday morning (Aug. 27) when the distance between Earth and Mars is least.
If you oversleep on August 27th, or clouds get in the way of Mars, don't worry. Mars will remain bright and beautiful for many weeks to come.
Right: Mars lies among the dim stars of Aquarius and Capricornus. [sky map]
"Many people have the misimpression that there is something special about the appearance of Mars on August 27th, as if it were substantially closer then than the day before or after," notes John Mosley of the Griffith Observatory in Los Angeles. "The reality is that Mars is close to earth all the month of August and will remain close all through September. The distances involved are great and they change little from one day to the next."
The best night, he advises, is any night when the air is steady and the skies are clear.
In fact, Mars is going to become easier to see during the weeks ahead simply because it rises earlier and earlier each day. By mid-September it will be high in the sky before bedtime--nearly as brilliant as it is now.
Travels and Trifles
It's been widely reported that this week's close encounter is the best in 60,000 years. True. But similar Earth-Mars encounters have happened many times in recent history. Some examples: Aug. 23, 1924 and Aug. 18, 1845. In both cases Mars and Earth were approximately 56 million km apart. The difference between those encounters and this one is less than about 50 thousand kilometers. A trifle.
Even more trifling is the difference between French Polynesia and other parts of Earth. Mars will look the same this week from Tahiti as it does elsewhere. Being a fewthousand kilometers closer to something 56 million kilometers away just doesn't make much difference.
On the other hand, a warm sea breeze, the crashing of waves on the beach, the ambiance of the South Pacific ... these factors may have some effect on Mars watchers beyond the ken of science. Perhaps a research expedition is in order. We leave that for the reader to decide.
Note: At the moment of Earth's closest approach to Mars, Mars will be directly above an open patch of Pacific Ocean near the Tuamotu Archipelago. The area is dotted with small islands; none are permanently inhabited. The nearest populated island is Tahiti, less than two degrees of latitude away from the "sub-Mars point."
Learn more about NASA's Mars Exploration Program
Approaching Mars (Science@NASA) -- Earth and Mars are converging for a close encounter in August. The red planet is already an appealing target for sky watchers.
Mars Dust -- (Science@NASA) Using only backyard telescopes, amateur astronomers are enjoying great views of dust clouds on Mars
Mars is Melting -- (Science@NASA) The south polar ice cap of Mars is receding, revealing frosty mountains, rifts and curious dark spots.
What is opposition? It's a time when Earth and Mars are close together--like August 27, 2003. The two planet go around the sun like runners on a track: fast-moving Earth on the inside lane and slower-moving Mars on the outside. Every two years, more or less, Earth laps Mars and the two planets are close together. From Earth, Mars and the sun appear on opposite sides of the sky--thus we say "Mars is at opposition."
Oppositions of Mars, 1901-2035 -- from The Planet Mars: A History of Observation and Discovery (University of Arizona press)
Perihelic Oppositions of Mars -- a table of our closest encounters with the Red Planet.
Images of Mars from the Association of Lunar and Planetary Observers (ALPO)
Making a Splash on Mars -- (Science@NASA) On a planet that's colder than Antarctica and where water boils at ten degrees above freezing, how could liquid water ever exist? Scientists say a dash of salt might help.
Once Upon a Water Planet -- (Science@NASA) Today the Red Planet is dry and barren, but what about tomorrow? New data suggest that the long story of water on Mars isn't over yet.