Seeing Stars with James Wooten: The Summer Triangle is high in the sky

This star map shows the Houston sky at 10 pm CDT on July 1, 9 pm CDT on July 15, and dusk on July 31.  To use the map, put the direction you are facing at the bottom. The Summer Triangle is high in the east.  This consists of the brightest stars in Cygnus, Lyra, and Aquila.  Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius to his left.  Leo, the Lion, sets in the west.  From the Big Dipper’s handle, ‘arc to Arcturus’ and ‘speed on to Spica’ in the southwest.  Watch Mars close in on Saturn this month.

This star map shows the Houston sky at 10 p.m. CDT on July 1, 9 p.m. CDT on July 15, and dusk on July 31. To use the map, put the direction you are facing at the bottom.
The Summer Triangle is high in the east. This consists of the brightest stars in Cygnus, Lyra, and Aquila. Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius to his left. Leo, the Lion, sets in the west. From the Big Dipper’s handle, ‘arc to Arcturus’ and ‘speed on to Spica’ in the southwest. Watch Mars close in on Saturn this month.

This month, Mars is in the southwest at dusk this month. Mars continues to fade a little each night as Earth continues to leave it farther behind. Still, Mars rivals the brightest stars we see at night.

Saturn is also in the southwest at dusk. This month and next, Mars approaches Saturn more and more. 

Venus remains in the morning sky. Look east at dawn for the brightest point of light there; only the Sun and Moon outshine Venus. Venus remains a morning star for almost all of 2014.

Jupiter is behind the Sun and out of sight this month. 

The Big Dipper is left of the North Star, with its handle pointing up. From that handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars are in the west at dusk. Leo, the Lion, is setting in the west at dusk.

Antares, the brightest star of Scorpius, the Scorpion, is in the southeast, with the ‘teapot’ of Sagittarius rising behind it. The Summer Triangle has fully risen in the northeast. The stars of summer are here.  

Moon Phases in July 2014:

1st Quarter: July 5, 7:00 a.m. 
Full: July 12, 6:26 a.m.
Last Quarter: July 18, 9:09 p.m.
New: July 26, 5:42 p.m.

At about 7 p.m. on Thursday, July 3, Earth is as far from the Sun as it will get this year. This is aphelion, when Earth is 94.56 million miles from the Sun, as opposed to the average distance of 93 million miles. On January 4, Earth was at 91.44 million miles from the Sun; that was perihelion (closest approach to the Sun). It turns out that this variation in the Earth-Sun distance is too small to cause much seasonal change. The tilt of Earth’s axis dominates as it orbits the Sun. That’s why we swelter when farther from the Sun and shiver when we’re closer. 

Click here to see what’s happening this month in the Burke Baker Planetarium

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. If you’re there, listen for my announcement. 

Clear skies!

The galaxy just got bigger: Calling all future space explorers to Family Space Day!

ATTENTION FUTURE SPACE EXPLORERS: NASA has just discovered 715 new planets for you to study and learn.

But let’s back up a second.

Launched in 2009, the Kepler space observatory has been scanning the heavens for earth-like exoplanets — planets existing outside our solar system. The observatory has been able to detect strong possibilities of planets, but they needed confirmation. Mountains of data have been sent to scientists on the ground to confirm the existence of these exoplanets.

While this process has been grueling and slow going, it resulted in several hundred confirmations. However, yesterday NASA announced the discovery of 715 new planets orbiting 305 stars — boosting the number of verified exoplanets by 70%.

Kepler has collected this data by detecting the transit of planets across their stars. When planets transit (i.e., cross in front of) a star, the star’s brightness appears to dim by a small amount. The amount of dimming depends on the size of the star and object revolving around it. This process can give false-positives, however, which has necessitated that the data be confirmed by scientists on the ground.

So what’s changed?

The way scientists were sifting through the data has changed. You see, it’s much easier to confirm the existence of planets when they are part of a multi-planet system. Readings that indicate multi-planet systems exist are difficult to explain as anything other than a multi-planet system — as opposed to single planet systems that could be explained by other phenomena. Therefore, by focusing on the data from what appeared to be multi-planet systems, scientists have been able to sift through and confirm the data at a much more rapid pace.

So what’s out there?

Ninety-four percent of the planets discovered are smaller than Neptune (that is, they’re four times larger than Earth or smaller). The number of planets with 2R (double the Earth’s radius) or less has increased 1,000 percent. Our total count of exoplanets now stands at 1,700 — which NASA planetary scientist Jack Lissaur has described as a “veritable bonanza of new worlds.”

So if you’ve got a future space explorer in your family, there’s never been a better time to get excited about space adventures — just in time for our Family Space Day at the George Observatory this Saturday.

Experience what it’s really like to be an astronaut-in-training with a simulated mission. Volunteers from NASA will guide you and your family on your mission — ensuring safe travels — as you transform into astronauts, scientists and engineers flying through space.

A perfect activity for the whole family, the flight simulation is open to adults and children 7 years and older (children ages 7 to 9 must be accompanied by a chaperone), and a minimum of 10 participants per mission is required.

Don’t miss this chance to participate in real astronaut training at the George Observatory! Click here or call (281) 242-3055 for details.

Go Stargazing! September Edition

Saturn leaves the evening sky in September 2011.  Face west southwest at dusk, and you’ll see Saturn near a star of similar brightness—Spica in Virgo.  Saturn is a bit to the right of Spica as you face southwest.

Each night this month, however, Saturn and Spica appear lower and lower to the horizon, until they set in twilight by mid-month.  When is the last night you can still see it?  Next month, Saturn is behind the Sun and invisible.

A Long Night Falls Over Saturn's Rings
Creative Commons License photo credit: NASA Goddard Photo and Video

Jupiter is now a late evening object.  It rises before 10:45 pm on September 1, and just after 8:30 pm by September 30.  Face east at the appropriate time and look for the brightest thing there—that’ll be Jupiter.   The King of Planets continues to dominate the southwestern pre-dawn sky.  Mars is now a bit higher in the east at dawn.  Although it has brightened, many of the stars in the morning sky outshine it.  However, as it moves from Gemini into dimmer Cancer, Mars is quite identifiable.  Venus was behind the Sun last month, and is still lost in the Sun’s glare.

Io Close-Up with New L8 Jupiter
Creative Commons License photo credit: FlyingSinger

The Big Dipper is beginning to pass under the North Star; Houstonians now need a clear northwestern horizon to see it at dusk.  From its handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars set in the west and southwest at dusk.  Antares, brightest star of Scorpius, the Scorpion, is in the southwest, with the ‘teapot’ of Sagittarius to its left.  Meanwhile, the Summer Triangle is virtually overhead.  The stars of summer now dominate the evening sky.  In late evening, you can watch the Great Square of Pegasus rise in the east.  Note that we look towards the center of our galaxy when we face between Scorpius and Sagittarius.  When facing the Great Square or especially south and east of that, we face out of the plane of our galaxy, a direction where there are fewer bright stars.  That’s why the large expanse of sky rising under Pegasus seems devoid of bright stars.

Moon Phases in September 2011:
First Quarter September 4, 12:39 pm
Full September 12, 4:26 pm
Last Quarter September 20, 8:39 am
New September 27, 6:08 pm

Autumnal Equinox

At 4:06 am CDT on Friday, September 23, the Sun is directly overhead at the equator.  This, then, is the autumnal equinox, a date when everyone in the world has the same amount of sunlight.  In the Northern Hemisphere, we’ve seen the days get a little shorter and the midday Sun a little lower each day since June 21.  For us, the season changes from summer to fall at the equinox.

In the Southern Hemisphere, people have seen the days lengthen and the midday Sun get a little higher each day since June.  For them, the season changes from winter to spring.

Rosh Hashanah

The New Moon of September 27 is the one closest to the fall equinox and therefore marks the Jewish New Year.  Rosh Hashanah is not on the New Moon itself but two days later on the 29th, when the slender crescent becomes visible in the west at dusk.

Astronomy Day 2011 at the George Observatory

Come join us anytime from 3 to 10 pm on October 8 for our annual Astronomy Day at the George Observatory. Dozens of telescopes—including our large research telescopes—will be available to give everyone a chance to enjoy the delights of the night sky, including star clusters, planets and galaxies.  Before dusk, we will have solar observing, Challenger Center simulations, outdoor and indoor presentations (beginning at 4) and many other activities!

Water on Mars?

On August 5, 2011, Science Magazine published a paper, announcing that astronomers had observed unusual features on the northward slopes of cliffs in Mars’ southern hemisphere. Strangely, these narrow, dark features are seasonal; they appear in spring and summer and disappear as fall approaches. So far, the explanation that best fits the evidence is that briny water sometimes flows on Mars.

Fourth Planet From The Sun

Mars, the fourth planet from the Sun, is just over half as big across as the Earth and almost one-ninth as massive. Mars takes almost two Earth years (687 days to be exact) to complete an orbit which, on average, is half again as big as ours.  However, Mars’ orbit is over five and a half times as eccentric, or out-of-round, as ours.  Unlike on Earth, then, the variation in Mars’ distance from the Sun is significant enough to influence its climate.

Similarly to Earth, Mars rotates on its axis once every 24.6 hours.  This axis is tilted by about 24.5 degrees, giving Mars seasons similar to those on Earth, whose axis is tilted by 23.5 degrees.  In its interior, Mars has no liquid outer core and therefore lacks a global magnetic field to deflect the solar wind away from its atmosphere.

Red Marble vs. Blue Marble
Creative Commons License photo credit: Bluedharma

These factors contribute to a climate where pure liquid water is highly unstable and cannot persist for long.

Due to its greater distance from the Sun, Mars is much colder than Earth.  Mars Global Surveyor measured temperatures ranging from zero to -113 degrees Celsius (32 to -170 oF).  Temperatures at the surface can be above freezing in summer, particularly in Mars’ southern hemisphere, because summertime there coincides with perihelion.  Even so, temperatures just one meter above the surface can be cooler than on the ground, as measured by Mars Pathfinder.  Nighttime temperatures at the poles can approach -200 oF, colder than the coldest temperature ever recorded in Antarctica (-129 oF).

Further, lack of a magnetic field means that Mars was unable to retain much of an atmosphere. 

Earth’s atmosphere is over 200 times as massive as that of Mars.  Although it is over 95% composed of carbon dioxide, such a tenuous atmosphere produces no significant greenhouse effect to raise temperatures on Mars.  Except at the very lowest elevations, the very thin Martian atmosphere exerts a pressure lower than the triple point of water; even on rare occasions when the temperature might be above freezing, ice sublimates rather than melting.

Why Salt Water Might Exist On Mars

Salt water, however, freezes at a lower temperature than pure water, and thus might remain liquid for brief periods on Mars.  Salt water (or brines), then, might explain observations made by NASA’s Mars Reconnaissance Orbiter, which has orbited Mars since November 2006.  Images from this orbiter’s High Resolution Imaging Science Experiment show features called Recurring Slope Lineae (RSL).  They are in Mars’ southern hemisphere, on the north (equator facing) slopes such as crater walls.  The RSLs appear in local springtime and persist until local autumn, when they vanish.  Only 0.5 meters to 5 meters wide, they can become hundreds of meters long during Mars’ southern summer.

Life Requires Water

We have always been interested in finding signs of water on planets other than Earth because life as we know it requires water to exist.  As the only other planet in our solar system with conditions even approaching ours, Mars is among the first places we looked for life beyond Earth.  The search for water, and thus possible life, has been a major goal of our robotic missions to Mars, including the Viking program in the 1970’s.

We have established that H2O exists on Mars in other phases. 

Mars’ polar caps are cold enough for dry ice (frozen carbon dioxide), but they contain water ice as well.  In 2005, the European Space Agency’s Mars Express satellite snapped a picture of an ‘ice lake’ in the bottom of a crater near Mars’ north pole. In 2008, the Phoenix lander revealed water ice in trenches dug by its robotic arm.  In 2004, the rover Opportunity took photos of water ice clouds and was also at times covered in frost, indicating water vapor had frozen onto the rover.

For liquid water, however, scientists had looked into Mars’ past.  Vastitas Borealis, a huge region between four and five kilometers lower than the mean elevation of Mars, fills much of Mars’ northern hemisphere.  It is also flatter, with craters in the Vastitas Borealis much rarer than on the rest of Mars.  Many scientists subscribe to the Mars Ocean Hypothesis, which posits that about 3.8 million years ago, Vastitas Borealis was the site of a vast ocean covering about one-third of Mars’ surface, which then either evaporated or froze into the ground as Mars’ environment ceased to support large bodies of liquid water.  For one thing, the size and shape of craters in Vastitas Borealis suggest that sublimation of water ice played a role in weathering them.  Also, there are networks of valleys resembling river systems on Earth, as if they once flowed into the ancient ocean.

A large water ocean could have persisted on early Mars

To support this ancient ocean, there are indications that Mars once had enough carbon dioxide to exert up to one bar of atmospheric pressure.  Under this higher pressure, combined with higher temperatures (due to the greenhouse effect) a large water ocean could have persisted on early Mars.  However, Mars lacks a global magnetic field; its atmosphere interacts directly with the solar wind.  This interaction would have gradually dispersed Mars’ atmosphere into space, a process we can observe today.  As the atmosphere went away, Mars would have lost its ocean due to the end of the greenhouse effect and the lower air pressure.

The existence of this ancient water ocean on Mars is not yet fully established; competing explanations such as wind erosion or liquid methane are not yet excluded.  Still, a former ocean 3.8 milllion years in Mars’ past has been our best bet for liquid water on the Red Planet.

Liquid Water on Mars Today

Until now, that is.  If confirmed by future observations, August 2011 would mark the first published evidence of liquid water on Mars today.  Yet many questions remain.  We know neither the source of the salty water, nor the precise mechanism that brings it to the surface, not to mention whether or not such water might contain germs.  So, the science we’re doing  at Mars continues, as the new questions raised make Mars an even more fascinating world to study.