Celestial lights

The Southern Cross and the Milky Way 
By Phyllis Burton Pitluga, May 4, 2007

For those who have always wanted to see the Southern Cross, face south toward a distant low horizon (midnight at the beginning of the month, 11pm at mid-month and 10pm 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). 

To the left, or east, are Alpha and Beta Centauri. Alpha Centauri is notable because it is our closest neighbor star at four light years away (24 trillion miles). It is actually made up of the light of three stars co-orbiting each other. Of the three, Proxima Centauri is truly the closest but it is a dim dwarf star. Alpha Centauri is very much like our own star, the Sun. Looking at it gives us an idea of what our star would look like from four light years away, rather than 8 light minutes—our distance from the Sun here on Earth. Alpha and Beta Centauri are considered to be the eyes of the celestial llama by people in the Andes Mountains of Peru and Bolivia. The body of the llama is a dark region along the white band of light of the Milky Way.

This time of year, the Milky Way rims our horizon here in San Miguel. Our Solar System is about two-thirds out from the center of our flattened disk of stars that make up the Milky Way. From Earth, when we look overhead now, we see the constellation of Coma Berenices forming a web of stars above us in our galaxy, between the bright star Regulus to the west and Arcturus to the east.

The Sun overhead at noon

Because San Miguel de Allende is below the Tropic of Cancer, the Sun passes overhead twice during the year: May 25–26 and again on July 18–19. Earlier in May, the Sun is south of overhead. After May 26, the Sun is north of overhead. The Sun continues to be ever farther north of overhead until the June Solstice on June 21. Then the Sun gradually returns to passing overhead on July 18–19. For the following 10 months, the midday Sun will be to the south.

To see the phenomenon of the sun directly overhead on May 25–26, go outside at Local Noon. Here in San Miguel, Local Noon is at 1:35pm (Daylight Savings Time = 1pm, and we are west in our Central Time Zone by 40 minutes = 1:40pm. Because the Earth is orbiting a bit slower in May so we return to noon five minutes earlier than average = 1:35 for Local Noon now.) Notice the shadows of trees, upright posts and your own shadow. 

Venus, Saturn and Jupiter still bright in the evening 

Venus continues to dominate the evening sky as the brightest object after the Sun and Moon. On a moonless night you can see shadows cast by its bright light and a pathway of light shining from Venus upon the still surface of a lake. In a telescope, you can see Venus gradually change shape in the weeks ahead. As it gets closer and bigger, it becomes a skinny crescent by late summer.

Saturn is near the star Regulus of Leo-the-Lion more than high in the southwestern sky. This planet is a treat even in small telescopes because of the beautiful icy rings that encircle it. Look for some of its bright moons orbiting it, as well.

Jupiter is rising in the eastern sky as darkness descends. Jupiter is the giant of the planets. In a telescope (or even binoculars), you can see four of its largest moons change position over an evening as they orbit Jupiter.


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



Sky calendar, May 2007 

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. 



May 2, Wednesday: The Full Moon rises at sunset, crosses the sky all night long then sets at sunrise.



May 5, Saturday: The annual Eta Aquarid meteor shower will be “raining” grains of extinct comet particles into our atmosphere from the eastern sky at about one a minute in the wee hours of the morning. Unfortunately the light of the Moon will interfere this year. On this same night, the Moon will be passing below the largest planet, Jupiter. 


May 9, Wednesday: Last Quarter Moon rises about 1am.


May 12, Saturday: The Moon passes above the red planet, Mars.


May 16, Wednesday: The New Moon is not visible because it has no sunlight shining upon the side that always faces the Earth.


May 17, Thursday: The slender Waxing Crescent Moon passes above Mercury, the planet closest to the Sun.


May 19, Saturday: The Waxing Crescent Moon passes above the brilliant planet, Venus.


May 21, Monday: The Crescent Moon passes above the Beehive star cluster.


May 22, Tuesday: The Crescent Moon passes just above the ringed planet, Saturn.


May 23, Wednesday: At sunset, the First Quarter Moon is half way across the sky from west to east and will continue orbiting eastward each evening. The Moon is passing just above the bright star Regulus in the constellation of Leo-the-Lion.


May 27, Sunday: The Waxing Gibbous Moon is passing below the bright star Spica in the constellation of Virgo-the-Maiden.


May 30, Wednesday: Venus is below (but also much closer than) the star Pollux of the Gemini Twins, Castor and Pollux.