Helping out junsupra's small article:
Approaching Mars
Earth and Mars are converging for a close encounter in August. The red planet is already an appealing target for sky watchers.
June 18, 2003: Count slowly: one one-thousand, two one-thousand, three one-thousand.... You just got about 30 km closer to the planet Mars.
Earth and Mars are rapidly converging. On August 27, 2003--the date of closest approach--the two worlds will be 56 million km apart. That's a long way by Earth standards, but only a short distance on the scale of the solar system. NASA, the European Space Agency and Japan are all sending spacecraft to Mars this year. It's a good time to go.
Right: This is what Mars looked like through the eye piece of an 8" telescope on June 11th. Image credit: Ron Wayman of Tampa, FL.
Between now and August, Mars will brighten until it "blazes forth against the dark background of space with a splendor that outshines Sirius and rivals the giant Jupiter himself." Astronomer Percival Lowell, who famously mapped the canals of Mars, wrote those words to describe the planet during a similar close encounter in the 19th century.
Already Mars is eye-catching. You can see it this month in the morning sky--bright, steady and remarkably red. Only Venus near the sun is brighter.
Amateur astronomers looking through backyard telescopes have reported in recent days great views of Mars's south polar cap. Made of frozen water and carbon dioxide ("dry ice"), it reflects sunlight well. "I can see the polar ice vividly using my 8-inch telescope," says Ron Wayman of Tampa, Florida. He's also spotted "some faint darker-shaded areas on the surface."
Such markings will become clearer in the weeks ahead. On June 1st Mars was 12.5 arcseconds across and it glowed like a -1st magnitude star. On August 27th it will be twice as wide (25 arcseconds) and six times brighter (magnitude -2.9).
Much has been made of the fact that the August 27th encounter with Mars is the closest in some 60,000 years. Neanderthals were the last to observe Mars so favorably placed. This is true. It's also a bit of hype. Mars and Earth have been almost this close many times in recent history.
Some examples: Aug. 23, 1924; Aug. 18, 1845; Aug. 13, 1766. In each case Mars and Earth were approximately 56 million km apart.
Astronomers call these close encounters "perihelic oppositions." Perihelic means Mars is near perihelion--its closest approach to the sun. (The orbit of Mars, like that of all planets, is an ellipse, so the distance between the sun and Mars varies.) Opposition means that the sun, Earth and Mars are in a straight line with Earth in the middle. Mars and the sun are on opposite sides of the sky. When Mars is at opposition and at perihelion--at the same time--it is very close to Earth.
August 27th is indeed the best perihelic opposition since the days of the Neanderthals, but it scarcely differs from other more recent ones. That's fine because all perihelic oppositions of Mars are spectacular.
Mars is a morning planet now. You have to wake up early to see it. Soon, though, it will be more conveniently placed. By mid-July Mars will rise in the east around 11 p.m. local time. In late August it will appear as soon as the sun sets. It won't be long before everyone can see Mars at a civilized hour.
We'll be telling more stories about Mars in the weeks ahead. This one, though, is finished. Did you make it to the end? Congratulations! You're now 2000 km closer to Mars.
MARS BIODATA
Orbital characteristics (Epoch J2000)[1]
Semi-major axis 227,936,637 km (141,632,976 mi)
1.523 662 31 AU
Orbital circumference 1,429,000,000 km (887,900,000 mi)
9.553 AU
Eccentricity 0.093 412 33
Perihelion 206,644,545 km (128,402,967 mi)
1.381 333 46 AU
Aphelion 249,228,730 km (154.863,553 mi)
1.665 991 16 AU
Orbital period 686.9600 d
(1.8808 a)
Synodic period 779.96 d
(2.135 a)
Avg. Orbital Speed 24.077 km/s (53,859 mi/h)
Max. Orbital Speed 26.499 km/s (59,277 mi/h)
Min. Orbital Speed 21.972 km/s (49,150 mi/h)
Inclination 1.850 61°
(5.65° to Sun's equator)
Longitude of the
ascending node 49.578 54°
Argument of the
perihelion 286.462 30°
Number of natural satellites 2
Distance from Sun 1.52 AU
Physical characteristics
Equatorial diameter 6,804.9 km (4228.4 mi)
(0.533 Earths)
Polar diameter 6,754.8 km (4197.2 mi)
(0.531 Earths)
Oblateness 0.007 36
Surface area 1.448×108 km2 55,907,000 square miles (144 798 465 square kilometers)
(0.284 Earths)
Volume 1.6318×1011 km3
(0.151 Earths)
Mass 6.4185×1023 kg
(0.107 Earths)
Mean density 3.934 g/cm3
Equatorial gravity 3.69 m/s2
(0.376g)
Escape velocity 5.027 km/s (11,245 mi/h)
Rotation period 1.025 957 d
(24.622 962 h)
Rotation velocity 868.22 km/h (539.49 mi/h)
(at the equator)
Axial tilt 25.19°
Right ascension
of North pole 317.681 43°
(21 h 10 min 44 s)
Declination 52.886 50°
Albedo 0.15
Surface temp.
- min
- mean
- max
133 K (−140 °C)
210 K (−63 °C)
293 K (20 °C)
Adjective Martian
Atmospheric characteristics
Atmospheric pressure 0.7–0.9 kPa
Carbon dioxide 95.32%
Nitrogen 2.7%
Argon 1.6%
Oxygen 0.2%
Carbon monoxide 0.07%
Water vapor 0.03%
Nitric oxide 0.01%
Neon 2.5 ppm
Krypton 300 ppb
Xenon 80 ppb
Ozone 30 ppb
Methane 10.5 ppb
Article source :
www.nasa.gov
