The arrival of the Phoenix Mars Lander
By Phyllis Burton Pitluga May 2, 2008 San Miguel de Allende

Artist’s concept of the Phoenix Mars Lander a moment before touchdown on the arctic plains of Mars. NASA/JPL-Caltech/University of Arizona.

Landing is targeted for 6:36pm on the arctic permafrost of Mars. If all goes well, the first signal will arrive 17 minutes later. Phoenix will slow the descent from 13,000 mph to 5 mph via a 39-foot parachute and rocket thrusters. Mars is our neighbor planet, half again as far from the Sun. Mars is half the size of Earth. It currently is in an Ice Age.

One of the goals of this mission is to determine if microbial life ever arose on Mars. This sophisticated lander has a robotic arm to dig a trench into the subsurface and a laboratory aboard to analyze samples. It is important to test samples from below the surface of Mars because its surface has been sterilized by proton and electron particles streaming from the Sun. Mars is not currently protected from this particle radiation by a magnetic field. Earth is.

Life developed on Earth in four steps: single-celled bacteria to complex cells, then specialized cells allowing complex life forms and finally to intelligent life with established language. We are eager to know if even the first step occurred on Mars or elsewhere in the solar system. Stay tuned.

See the Southern Cross

For those who have always wanted to see the Southern Cross, face south toward a distant low horizon (11pm at the beginning of the month, 10pm at mid-month and 9pm at the end of the month). The Southern Cross is just above the horizon. Its four bright stars form a cross (the right cross star is dimmer).


Overhead sun on May 25-26

Because San Miguel de Allende is 20 degrees north of the equator, south of the Tropic of Cancer, the Sun passes overhead twice during the year at local noon (about 1:35pm CDT) May 25–26 and again July 18–19. Earlier in May, the Sun is south of overhead at local noon. After May 26, the Sun is north of overhead at local noon. The Sun continues to be ever further north of overhead until the solstice on June 20. Then the Sun gradually returns to passing overhead July 18–19. For the following 10 months, the midday Sun will be to the south.

Phyllis Burton Pitluga is Astronomer Emerita at Adler Planetarium & Astronomy Museum, Chicago. She is now a resident of San Miguel.



Sky Calendar May 2008

By following the Moon as the biggest and brightest “pointer” in the sky, during the month you can identify different planets and bright stars. On following nights you can relocate them but without the Moon—the Moon moves about 25 times its own diameter from one night to the next. The Moon is much closer than the planets of our solar system and the stars are even farther. So, when the Moon appears close to a celestial light they are truly separated by millions, billions or trillions of miles.

At the beginning of May, in evening twilight, Mercury is low in the west, Mars about two-thirds up in the west and Saturn high overhead.

May 5, Monday: New Moon when the side facing Earth has no Sun shining on it. The Eta Aquarid meteor shower rises about 3am and rises higher in the east as dawn approaches. You can expect to see about 60 shooting stars an hour. These are sand-sized grains from a decayed comet.

May 6, Tuesday: The waxing Crescent Moon will be above Mercury with the Pleiades star cluster between them. The crescent is sunlight shining directly onto the Moon. Notice how you can see the night side of the Moon, too. This is because the nearly Full Earth is shining onto the nighttime side of the Moon. Think about how bright moonlight is. Well Earthshine is much brighter because the Earth is bigger and has white clouds in its atmosphere to reflect more sunlight.

May 10, Saturday: The Moon passes above the red planet Mars.


May 11, Sunday: First Quarter Moon is halfway across the sky as the Sun sets in the west.

May 12, Monday: The star Regulus is above the Moon and Saturn is higher above the Moon.


May19, Monday: The Full Moon rises opposite the setting Sun, crosses the sky all night long as the Earth rotates, and sets at sunrise.

May 24, Saturday: The waning Gibbous Moon passes below the brilliant planet Jupiter.

May 27, Tuesday: Last Quarter Moon rises at midnight and sets at noon.