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
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
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
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
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
• 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
• 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: email@example.com.
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,
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.