The surface of the planet Mercury

Enjoy our starry night sky

Be a considerate neighbor: Reduce nighttime glare.
Shield your outside lights downward, so no glare goes up to dull the night sky (or into your neighbor’s windows) and enjoy the beautiful, stars above.

May 2008 Night Sky

—CHARLIE CHRISTMANN

MERCURY

This month, Mercury is in the spotlight. No, not the chemical element found in compact fluorescent lights, but the planet closest to the Sun. Only two spacecraft have visited this strange world. The first was Mariner 10, which made three passes in 1974 and 1975. Just recently, the Messenger spacecraft flew past Mercury in January of this year. Messenger is planning another flyby in October 2008 and again in September 2009 before settling into orbit in March 2011.

Being so close to the Sun all the time, Mercury is difficult to observe. Its greatest elongation from the Sun is only 28.3 degrees and it makes one complete orbit of the Sun every eighty-eight days. Mercury oscillates back and forth from being a morning star to an evening star, usually spotted near its maximum elongation low in the sky.

Since Pluto was demoted to a minor planet, Mercury is now the smallest of the true eight planets orbiting the Sun with a diameter of only 3,031 miles (the Moon’s diameter is 2,159 miles). At one time, scientists thought that one side of Mercury always faced the Sun, something called tidal locking, where the planet spins once on its axis for each orbit around the Sun. But radar observations in the mid-60s showed that the planet actually rotates three time on its axis for every two orbits, making a solar day (Sun going from being overhead back to being back overhead) about 176 Earth days long while taking only 58.7 Earth days to actually spin once on its axis. The planet also has a somewhat egg-shaped orbit ranging from 28.5 million miles to 43.5 million miles from the sun.

All of this weird spinning and orbiting has an interesting effect. Observers at some locations on Mercury could watch, once a Mercurian year, the sun rise about halfway up the sky only to fall back from where it rose and set, only to rise later on the same horizon all in one Mercurian day. The stars would also be moving about three times faster than normal in the night sky. Standing at other points on Mercury would offer different, but equally bizarre motions in the sky.

Actually making telescopic observations of Mercury is hard, since the planet lives in the glare of our own star. The Hubble telescope must avoid looking at this planet for fear of damaging its optics and cameras.

From images made by the visiting spacecraft, Mercury seems more like our own Moon than a planet. It is heavily-cratered from its bombardment by meteors and comets inbound to the Sun about 3.8 billion years ago. Since it has no atmosphere, even the smallest of meteors made their marks on the surface. Even today, as debris from the solar system is pulled in by the Sun’s gravity, Mercury is in the crosshairs.

Even if you could do without any atmosphere, living on Mercury would be unpleasant at best. The average planetary temperature is 354 degrees Fahrenheit with the temperature ranging between 280 and eight hundred degrees. Olympic athletes would do well there, however. Gravity on Mercury is only about a third of Earth’s.

The surface of Mercury has tremendously steep slopes and long cliffs from erosion or faulting, some are hundreds of miles in length and up to two miles high. Some of the cliffs cut through rings of craters and other surface features. This may indicate that they were formed by compression. It is thought that the surface area of Mercury shrank by about 0.1 percent after it had formed. In addition to its heavily cratered terrain, Mercury has regions of relatively smooth plains. These plains have been formed by ancient volcanic activity, but some may be deposits of dirt ejected from craters by impacts. Looking back at old Mariner data there is even some evidence of recent volcanic activity on Mercury. Amazingly, radar observations from Earth of Mercury’s north pole, not yet mapped by any visiting spacecraft, showed evidence of water ice in the shadows of some craters.

THE PLANETS AND THE MOON

• Mercury is an evening planet hovering low in the west after sunset. On the 4th, look for a great show as the Moon and Mercury converge in the evening sky. About forty-five minutes after sunset, Mercury will be easier to spot about two degrees below the thin crescent moon.

• Venus will be rising only about fifteen minutes ahead of the Sun, a difficult target to spot.

• Mars is high in the southwest at sunset. Mars will set in the west between 1:30 a.m. and 12:30 a.m. this month. May 10th is astronomy day, and Mars and the Moon put on a show this evening about one-and-a-half hours after sunset. Mars will be seven degrees to the right of the Moon. A bit more to the right will be the twins Castor and Pollux with bright Capella further to the right. Procyon will be below the Moon and Betelgeuse will be low on the western horizon. Look hard to find Mercury to the right of Betelgeuse and below Capella on the horizon.

• Jupiter clears the eastern horizon about 1:00 a.m. early in the month to 11:10 a.m. late in the month. There is a Jupiter–Moon conjunction on the 24th. Look in the south at least forty-five minutes before sunrise to see Jupiter four degrees above the waxing gibbous Moon.

• Saturn sets after midnight in the west this month. You can find it high in the southwest after sunset. Look for Saturn and the Moon in the southwest on the 12th. The bright star below and to the right of Saturn is Regulus.

• The Moon will be new on the 5th. This is also the Moon’s perigee (closest to Earth) at 222,308.6 miles. The Full Moon is on Canadian Victory Day, the 19th at 8:11 p.m. MDT. Lunar apogee (farthest from Earth) is on the 20th at 252,526.5 miles.

If you have a question or comment for Charlie, you may email him at: k5cec@yahoo.com.

Astro Bits

Rio Rancho Astronomical Society hosts meeting and stargaze

The Rio Rancho Astronomical Society (RRAS) will host its monthly meeting on Saturday, May 3 at the Coronado State Monument, starting at 8:00 p.m. Our special guest speaker will be Mark Boslough, who will talk about a possible meteor impact in Egypt at the dawn of history. A public stargaze will follow the meeting, weather permitting, and a variety of telescopes provided by members of the RRAS will show great views of Mars and Saturn, as well as elusive deep-sky objects such as galaxies, nebulae, and star clusters. Both events are free and open to the public.

The Coronado Monument is located on Highway 550 in Bernalillo, between Jackalope and the Warrior 66 gas station. For more information, visit www.rrastro.org or call 220-5492.

Stargazing at Chaco Canyon

The Albuquerque Astronomical Society (TAAS) and the Chaco Culture National Historical Park will co-host an evening of free public stargazing at the Chaco Observatory on Saturday, May 3, 2008. The dark skies of the Chaco Canyon and the instruments at the observatory together provide great views of planets, as well as more elusive deep-sky objects such as galaxies, nebulae, and star clusters. The park also hosts evening observing programs on Tuesdays, Thursdays, and Saturdays from April thru October. Observing begins at sunset, weather permitting, and is suitable for all ages. Admission to the park costs $8 per car load. There is no additional fee for admission to the evening observing programs.

Chaco Canyon is located in northwestern New Mexico. The recommended access route to the park is from the north, via US 550 (formerly NM 44) and County Road (CR) 7900, and CR 7950. From the north, turn from US 550 at CR 7900--3 miles southeast of Nageezi and approximately 50 miles west of Cuba (at mile 112.5). This route is clearly signed from US 550 to the park boundary (21 miles). The route includes 8 miles of paved road (CR 7900) and 13 miles of uneven dirt road (CR7950). For more information, visit the Chaco Culture National Historical Park website at www.nps.gov/chcu or call the Chaco Culture National Historical Park at (505) 786-7014. You may search the website for “night sky” to find additional information about the night sky program at Chaco Canyon.

Stargazing in the Manzanos

The Albuquerque Astronomical Society (TAAS) and the Sandia Ranger District will co-host an evening of free public stargazing in the Manzano Mountains on Saturday, May 31 at the Oak Flat Campground. Other 2008 event dates in this popular Saturday evening stargazing series are June 28, July 26, August 23, September 6, and October 4. The dark skies of the East Mountains and the large telescopes of TAAS astronomers together provide great views of planets, as well as more elusive deep-sky objects such as galaxies, nebulae, and star clusters.

Observing begins at sunset, weather permitting, and is suitable for all ages. Picnic facilities are available for those who would like to come early, and adjacent parking is available. Alcoholic beverages and pets are not allowed in the telescope viewing area. To get there, take NM Highway 337 nine miles south of the Tijeras exit on I-40, and follow the signs to Oak Flat and Juniper Loop. For more information, visit http://www.taas.org or call (505) 254-TAAS.