Two Stargazers for the price of one this time! ~Paul
July 12, 2008
Stargazer #483A
Learning the Night Sky Class
The Stargazer, in cooperation with the Central Texas Astronomical Society, is offering a free four-session "Learning the Night Sky" course the evenings of Aug. 18-21. Designed for novices, the course is for those who wish to begin learning the basics of stargazing and the constellations of summer.
The Aug. 18 & 19 sessions will be indoor classes from 7:30 - 9:30 p.m. held at the Stargazer's residence at 918 N. 30th St., Waco. These sessions include understanding how the night sky moves, cosmic and angular distances, solar system and deep space objects for observation, and basic stargazing equipment.
The Aug. 20 & 21 sessions will be outdoor under-the-stars classes from 8:30 - 10:00 p.m. to be held at a yet-to-be-determined dark-sky site beyond city lights. (The dates of the outdoor sessions are subject to change if the sky is cloudy.)
In the outdoor sessions participants begin learning the season's major constellations--a goal that can sound daunting. However, the Stargazer has devised a system which makes the task surprisingly do-able. The night sky is partitioned into nine regions, each of which has a story or theme to tie together the constellations within that region. Some stories come from antiquity while others are Stargazer originals, but all are fun, entertaining and helpful learning tools.
This class will focus on four regions prominent in the summer: circumpolar, macho quadrangle, Sagittarius's tea party, and the Milky Way triangle.
We will also learn about planets--where to look for them and how to tell them from the stars. By chance, six planets--Mercury, Venus, Mars, Jupiter, Neptune and Uranus--will be out in the early evening.
No prior experience is required, and participants need no equipment beyond materials for taking notes if they wish. The course closely follows the Stargazer's book, A Beginner's Guide to Learning the Night Sky, so it will be available for $25. However, purchasing the book is not required and loaner copies may be borrowed at no cost.
All ages are welcome although children at least 10 years of age have worked out the best in prior classes. Since parents are the best judge of their children's interest, attention span and potential for disruptive restlessness, they can best decide the appropriateness of this course for their children and vice versa.
There is no charge for the course, but registration is requested for planning purposes. To register or learn more, contact the Stargazer at 254-753-6920 (home), 254-723-6346 (cell) or paulderrickwaco@aol.com.
July 12, 2008
Stargazer #483B
Telling Planets from Stars
Currently early evening stargazers see Saturn and Mars setting in the west and Jupiter rising in the southeast. But in a sky full of stars, telling which ones are the planets isn't easy.
To the naked eye, planets appear as starlike points of light, and like stars, they are of different brightness and colors. So how can one tell which are planets and which are stars?
There are five naked-eye planets--Mercury, Venus, Mars, Jupiter, and Saturn--but the number of these planets visible on any given night varies from none to five. And the number even changes throughout the night as planets rise and set.
For casual stargazers, there is no foolproof way to pick out the planets from among stars, but the following pointers can help.
First, note the brightness. Venus and Jupiter always outshine all stars, and Mercury, Mars, and Saturn usually outshine all but the brightest stars. So brightness is one clue.
Second, you've likely heard that "stars twinkle, planets don't," which is often true. But this difference is subtle and varying. Twinkling is caused by turbulence in Earth's atmosphere, so that greater turbulence produces more twinkling while steadier air makes for less twinkling. So, when the stars twinkle noticeably, look for any brighter objects that don't.
Third--and this is very helpful--relates to where in the sky to look. Planets orbit the Sun on nearly the same plane, so they all closely follow the Sun's path across our sky, called the ecliptic. The Moon orbits Earth on nearly this same plane, so it too travels close to the ecliptic.
Like the Sun, the planets (and Moon) generally rise in the east and set in the west. Facing south with your arms stretched out slightly more than 180 degrees, any visible planets will be in front of your arms--never behind you or straight overhead. All that are above the horizon will be somewhere along the great ecliptic arc beginning in the east, rising and tilting to the south, and ending in the west.
One caveat. The season and time of night affect the ecliptic's exact rising and setting points, making them sometimes a little left or right of due east and west. And the amount of southerly tilt varies so that sometimes the ecliptic is tilted more than half way down toward the southern horizon while at other times it reaches nearly straight up. Still, knowing the approximate path is useful in identifying planets.
When not hidden in the Sun's glare, Venus and Mercury (the inner planets which orbit near the Sun) are only seen in the west after sunset or in the east before sunrise--never deep into the night. The outer planets, when not passing behind the Sun, might rise or set, and thus be seen, any time during the night.
This column always tells which naked-eye planets are visible in the morning and evening, and where to look for them. More precise information is available in monthly magazines like Sky & Telescope and Astronomy, and from websites like www.skymaps.com, www.skyandtelescope.com, and www.astronomy.com.
- Next Two Weeks. Avg. sunrise: 6:36 a.m.; avg. sunset: 8:33 p.m. (exact for Waco, TX)
* Tomorrow (July 13) evening the Moon is to the right of Scorpius' brightest star Antares in the south.
* Friday, July 18, the full Moon is called Thunder Moon and Hay Moon.
* The Moon is at 3rd quarter July 25.
- Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth's west-to-east rotation.)
Evening: Reddish Mars and brighter Saturn are low in the west with Jupiter climbing higher in the east.
Morning: An hour before sunrise Mercury is very near the east northeastern horizon as Jupiter is setting in the west southwest.
June 28, 2008
Stargazer #482
Evening Rendezvous in the West
Over the next two weeks Saturn and Mars, Leo's brightest star Regulus, and the Moon will rendezvous low in the west just after dusk. It's an event to begin watching nightly.
This evening ruddy-colored Mars is three moonwidths to the lower right of the slightly brighter Regulus with brighter Saturn to their upper left. An hour after sunset as twilight turns into darkness, the trio will be hard to miss two and one-half fist-widths (held at arm's length) above the western horizon.
Monday and Tuesday evening Mars passes within two moonwidths to the upper right of Regulus. Their close proximity provides an opportunity to observe how "stars twinkle, planets don't." While this adage is usually true, it is less obvious when objects are near the horizon and seen through more of Earth's atmosphere. There even planets can twinkle some.
By continuing to observe nightly, you'll see Mars approach Saturn. July 4, when you're out watching fireworks, notice how the three are aligned and almost equally spaced.
July 5 the Moon joins the trio to their lower right. The four will be aligned from the upper left to lower right.
The next evening presents what might be the highlight of the entire show as the crescent Moon moves to the trio's left. With your hand extended at arm's length, you can hold the Moon, two planets and a star in the palm of your hand.
By July 7 the Moon is well to the trio's upper left, and getting bigger and brighter. But the show still isn't over.
July 8-11 Mars passes less than two moonwidths to Saturn's lower left. Their closest approach comes July 10 when they are little more than a moonwidth apart.
- Next Two Weeks. Avg. sunrise: 6:29 a.m.; avg. sunset: 8:37 p.m. (for waco, TX)
* Sunset tomorrow night is the latest for the year at latitude 30 degrees North.
* Monday morning the Moon is less than 4 moonwidths below the Pleiades star cluster low in the east.
* Tuesday morning, an hour before sunrise low in the east, look for a thin crescent Moon and the star Aldebaran to its right a little more than the width of your fist held at arm's length; between them nearer the horizon is Mercury, the same brightness as the star.
* Wednesday is the midpoint of the year 2008, and the Moon is new.
* Friday the Earth is at aphelion, its farthest from the Sun in its elliptical orbit, at 94.3 million miles.
* Friday evening, an hour after sunset, the thin crescent Moon is to the left of the Beehive cluster low in the west -- use binoculars to spot the cluster.
* July 9 the Moon is at 1st quarter, and Jupiter is at opposition (on the opposite side of Earth from the Sun) when it rises at sunset, is up all night and sets at sunrise.
- Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth's west-to-east rotation.)
Evening: Saturn and Mars are low in the west; Jupiter is rising in the east.
Morning: Mercury is near the eastern horizon an hour before sunrise; Jupiter is low in the southwest.
- StarDate. A reader asked Stargazer to list the stations that carry the University of Texas McDonald Observatory's popular daily "StarDate" radio program. The two-minute program is carried by over 500 stations nationwide and 25 in Texas--far too many to list here. So here's how to find a station in your area. On the Internet go to StarDate. Under the Radio button, select Find Affiliates, then enter your state. Up will pop a list of cities, stations (with their frequencies) and air times.
June 14, 2008
Stargazer #481
Tunguska Event
A hundred years ago, on June 17, 1908, an event occurred over a remote part of Russia, the likes of which had not been seen before or since. Something exploded 3-6 miles in the air with far more power than the atomic bomb dropped over Hiroshima in 1945.
A little after 7 a.m. near the Podkamennaya Tunguska River in Siberian Russia, the sky blazed with light, the ground shook like an earthquake, thunder-like explosions were heard and blasts of hot wind blew people off their feet. Many who witnessed--and survived--the event feared the world was coming to an end.
The result was the virtual devastation of a forest area some 30 miles in diameter where an estimated 80 million trees were felled with their bark and branches stripped off. Surely any animals and humans in the ground-zero area would have been killed.
Fortunately the explosion happened over a largely uninhabited area, but it has been calculated that if it had occurred 5 hours later, it would have exploded over St. Petersburg. Given the devastation of Hiroshima with a much less powerful bomb, one shutters to think of the effects of this event over a large city.
So what was it? Since it happened years before the creation of nuclear bombs and when human flight was still in its infancy, it was almost certainly of natural rather than human origin.
A number of hypotheses have been put forth, including a few rather wild ones. Some have suggested that Earth was impacted by a black hole or antimatter; others have postulated that an alien spacecraft exploded while trying to land on Earth.
While none of these ideas can be unequivocally disproved, all lack the supporting evidence to be taken seriously. Most scientists think a comet or meteoroid several 10's of meters in diameter exploded shortly before impacting Earth's surface--a hypothesis backed by good, although not conclusive, evidence.
So what's the prospect of a repeat? No one can predict for sure, but the late Gene Shoemaker, an impact expert, estimated that these events might be expected once every 300 or so years.
- Next Two Weeks. Avg. sunrise: 6:24 a.m.; avg. sunset: 8:37 p.m.
(for Waco, TX)
* Wednesday's full Moon is called Rose Moon, Flower Moon, and Strawberry Moon.
* Friday is the summer solstice, the longest day of the year, marking the beginning of summer.
* After rising around 10:30 p.m. the evening of June 19, the Moon and Jupiter travel across the sky together all night.
* The Moon is at 3rd quarter June 26.
- Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth's west-to-east rotation.)
Evening: As darkness falls Mars and Saturn are setting in the west.
Morning: Brilliant Jupiter, rising soon after 10 p.m. is seen in the southwest by morning while Mercury begins its morning stint low in the east.
May 31, 2008
Stargazer #480
Where Are Venus and Mercury?
Other than the Moon and fleeting objects like bright meteors and artificial satellites, the planet Venus is the brightest body in our night sky. It far outshines all the stars and other planets. And Mercury, although most have never seen it, also gets brighter than any star.
But as bright as they are, these two innermost planets orbit nearer the Sun than does Earth and thus are seen only in the morning or evening, never in the middle of night. When blazing in the morning sky, Venus is called the "morning star," and when in the evening, the "evening star."
At the moment, neither Venus nor Mercury is readily visible as both are hidden in the glare of the Sun.
Venus spends some eight months as the "morning star" before hiding from view for some six weeks while passing behind the Sun (a position called superior conjunction). It then becomes the "evening star" for eight months before again hiding from view for another six weeks when it passes between the Earth and Sun (called inferior conjunction).
This 584-day cycle, repeated year after year, was well known to several ancient civilizations, like the Mayas of Central America for whom Venus was an important god.
This year Venus passes directly behind the Sun June 8. It then begins its stint as the "evening star" in early July, and remains in the evening sky the rest of 2008.
Mercury follows a similar but more rapid pattern with a 116-day cycle. Being nearest the Sun, Mercury speeds around our star faster than any other planet, zipping along at 107,000 mph and completing its orbit in a mere 88 Earth-days. (For comparison, Venus travels 78,000 mph, orbiting the Sun every 225 Earth-days, and Earth, traveling 67,000 mph, orbits the Sun every 365 days.)
Owing to its more elliptical and tilted orbit, Mercury's periods of visibility and invisibility are more varied. On average, it spends some six weeks in the morning sky, two weeks hidden in the glare of the Sun, six weeks in the evening sky and another two weeks in the Sun with the cycle being repeated about three times each Earth year.
June 7, the day before Venus is at superior conjunction behind the Sun, Mercury by coincidence is at inferior conjunction between the Earth and Sun. So as Venus is about to emerge in the evening sky, Mercury will soon appear in the morning sky.
- Next Two Weeks. Avg. sunrise: 6:23 a.m.; avg. sunset: 8:32 p.m. (for Waco, TX)
* The Moon is new Tuesday.
* The evening of June 7 the crescent Moon is below Mars with the Beehive cluster to the lower right.
* The next evening the Moon is below the star Regulus with Saturn above them.
* The Moon is at 1st quarter June 10.
* June 11 is the year's earliest sunrise at latitude 30 degrees north.
* June 13 is Friday the 13th, an unlucky day for the superstitious, but they're in luck as this is the only one this year.
- Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth's west-to-east rotation.)
Evening: Mars is three fists (held at arm's length) above the western horizon with Saturn the brightest object two fists to Mars' upper left.
Morning: Jupiter is the brightest object in the south.
May 17, 2008
Stargazer #479
Mars Passes Through the Beehive
The night sky is about to present an early evening show well worth a look--not a flashy display like a meteor shower or lunar eclipse, but still one to behold. The planet Mars is approaching the Beehive, a subtle but fairly large star cluster, which it will pass through May 21-23.
Although much smaller, Mars greatly outshines the stars of the cluster due to their greater distance. Mars is a modest-sized planet--twice the diameter of our Moon and half that of Earth. And like all planets and moons, Mars shines by reflecting sunlight. Every other year when its orbit brings it near Earth, it grows brighter, sometimes outshining the stars and rivaling bright Jupiter. But when further away--like now--it appears only as a moderately bright and slightly reddish star. At its nearest, Mars comes within 34 million miles of Earth.
The Beehive is composed of over 200 stars 515 light years away--more distant than most of the naked-eye stars in our night sky. Like our Sun, each star in the Beehive cluster emits light from the nuclear reactions deep within its core. The cluster's brighter stars are spread over a region of space 11 light years in diameter. For comparison, Alpha Centauri, our nearest neighboring star, is 4 light years away, and Sirius, our night sky's brightest star, is less than 9 light years distant.
Yet as huge as the cluster is, from Earth it covers an area only somewhat larger than a full Moon. To the naked eye, it looks like a faint, softly glowing stellar cloud with individual stars eluding detection. Through binoculars, however, the Beehive is at its dazzling best as several dozen stars swarm into view, giving rise to its name. Unless viewed at very low power, the entire Beehive won't fit into a telescope's field of view.
Mars spends three nights passing through the cluster, but several nights before and after will also be exciting, so start looking now. Here's how to find this beautiful sight.
Around 10 p.m., face west--a little to the left of where the Sun went down. The width of your fist held at arm's length being 10 degrees, look for the bright star, Procyon, 16 degrees above the horizon. Mars, a little fainter than the star, is 20 degrees further up. Don't be confused by Gemini's almost equally bright stars, Pollux and Castor, 15 degrees to the lower right of Mars. Using binoculars--any size will do--be prepared to have your socks knocked right off your feet.
- Next Two Weeks. Avg. sunrise: 6:27 a.m.; avg. sunset: 8:24 p.m. (for Waco, TX)
* Monday's full Moon, called Planting Moon and Milk Moon, occurs almost at apogee when the Moon is farthest from Earth in its elliptical orbit, thus it appears slightly smaller than most full Moons.
* The morning of May 24 the Moon is below Jupiter.
* The Moon is at 3rd quarter May 27.
* In the early evenings of May the Milky Way seems to disappear as it lies flat around the horizon.
- Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth's west-to-east rotation.)
Evening: Mercury is very low in the west at dusk with Mars higher in the west and Saturn well to Mars' upper left.
Morning: Jupiter is the brightest object in the south.
- Star Party. The Central Texas Astronomical Society hosts its free monthly star party May 24 at the Waco Wetlands beginning at 8:30 p.m. An indoor program is followed by a laser-pointer guided tour of the night sky and telescope viewing, weather permitting. For directions see my Website.
May 3, 2008
Stargazer #478
Phoenix to Look for Martians
Imagine a Martian exclaiming to a friend, "The Earthlings are coming again, and this time they're looking for us!"
That's what any thinking Martians could be saying--if any existed, which they probably don't. But what about non-thinking Martians, or long-ago Martians? Do they or did they exist?
That's what NASA is hoping to learn more about when the Phoenix spacecraft lands on Mars May 25. While Phoenix isn't actually carrying Earthlings, it is packed with an array of our scientific instruments to analyze the chemistry and mineralogy of Martian soil and ice, looking for indications of current or past life.
As countless science fiction books and movies can attest, we have long been fascinated with the idea of life on Mars. Yet early explorations dampened our hopes for actually finding life. Mars is incredible cold, it seemed bone-dry, and its atmosphere is too thin and oxygen-poor to sustain life as we know it.
Recent discoveries, however, have resurrected our hopes. Strong evidence for the presence of water, a prerequisite to life, has been found in the form of gaseous water vapor in Mars' atmosphere and water ice a short distance beneath Mars' surface. There are also indications that liquid water flowed on Mars as recently as 100,000 years ago. Geologically, that's like yesterday. Finally, scientists have found life thriving here on Earth in extreme conditions previously thought far too harsh for life even to exist, much less thrive.
According to NASA, "It is possible that bacterial spores can lie dormant in bitter cold, dry, and airless conditions for millions of years and become activated once conditions become favorable." If so, then "such dormant microbial colonies may exist" on Mars.
NASA's Mars Exploration Program, of which Phoenix is one component, has several goals: learn about Mars' climate and geology; determine whether life ever arose on Mars; and prepare for human exploration.
The specific goals of the Phoenix Mission are to study the history of water in Mars' north polar region, search for evidence of a habitable zone, and assess its biological potential.
So, while Phoenix might not actually find any Martians, it could well give us a much better idea of whether they exist, or have existed in the past.
- Next Two Weeks. Average sunrise: 6:36 a.m.; average sunset: 8:14 p.m. (for Waco, TX)
* Monday morning in the hours before dawn, the Eta Aquarid meteor shower peaks without interference from the new Moon.
* Tue. evening a very thin crescent Moon is above Mercury with the star Aldebaran to their left just above the west northwestern horizon an hour after sunset; use binoculars.
* Fri. evening the Moon is below Mars.
* The evening of May 10 the bright Moon is above Mars and grazes the Beehive star cluster; use binoculars to see the cluster to the Moon's upper right.
* May 11 the Moon is at 1st quarter.
* The evening of May 12 the Moon is to the left of Saturn with the fainter star Regulus below the planet.
* The early evening of May 13, Mercury is at it best, being at its highest above the setting Sun (called greatest elongation.)
- Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth's west-to-east rotation.)
Evening: Mercury is near the west northwestern horizon at dusk with Mars high in the west and Saturn higher in the south.
Morning: Jupiter is the brightest object in the south.
April 19, 2008
Stargazer #477
The Big Dipper As Your Nighttime Guide
The Big Dipper is probably the night sky's most familiar star pattern, and it's no wonder. It's visible from most of the northern hemisphere where over half of all humans live. And it really looks like a large dipper or ladle, although other cultures associate it with other objects such as a plow, a wagon or a bear. As well known as it is, the Big Dipper isn't an official constellation, but rather is a part of the huge constellation Ursa Major, the Big Bear.
Whether seen as a bear, a dipper or something else, the Big Dipper is a useful pattern in the night sky. The end stars of the bowl point to the North Star (also named Polaris), and are called the "pointer stars." The North Star is directly above Earth's North Pole and seems to never move in our sky. As Earth revolves on its axis every 24 hours, the Big Dipper swings around in a big counterclockwise circle with the pointer stars always showing the way to Polaris.
The old slave song "Follow the Drinkin' Gourd," referring to the Big Dipper, gave directions to run-away slaves traveling at night. The drinking gourd always pointed to the North Star, directing them north to freedom in Canada.
While it still points modern-day stargazers to Polaris, it helps in other ways as well. The curved handle "arcs to Arcturus," a bright reddish star 30 degrees away in the constellation Bootes. (The width of your fist held at arm's length is 10 degrees.) The spring constellation Leo, the Lion, when above the horizon, is seen 40 degrees from the bottom of the bowl, and winter's Gemini and Auriga are 45 degrees in front of the bowl.
During the evenings of fall, the Big Dipper swings below the horizon and is all but absent from our sky. According to an old Stargazer legend, it's during the fall that the dipper is near the Earth filling its bowl with water. In the winter, with the dipper east of Polaris, the water is frozen solid. During spring, with the dipper upside down above Polaris, the thawed water pours spring rains upon Earth. Then during the summer, with the dipper to the west of Polaris, the land is hot and dry because the dipper has no water left to cool and moisten the Earth.
- Next Two Weeks. Avg. sunrise: 6:48 a.m.; avg. sunset: 8:05 p.m. (for Waco, TX)
* Tomorrow's full Moon is called Grass Moon and Egg Moon.
* Wed. morning the Moon is to the right of the reddish star Antares.
* The morning of Apr. 27 the Moon is below Jupiter.
* The Moon is at 3rd quarter Apr. 28.
* May 1 is May Day, a cross-quarter day celebrating the middle of spring.
* The evening of May 2 Mercury passes near the Pleiades star cluster just above the western horizon an hour after sunset; binoculars will help.
- Naked-eye Planets. Evening: Mars is high in west with Saturn high in the south. Morning: Venus is sinking into the rising Sun as Jupiter is climbing higher in the southeast.
- Star Party. The Central Texas Astronomical Society hosts a free public star party April 26 at the Waco Wetlands beginning at 8 p.m., weather permitting. For directions to the Wetlands, see MAPS & DIRECTIONS elsewhere in this website.
April 05, 2008
Stargazer #476
Cosmic Sizes and Distances
Tuesday evening the crescent Moon will graze the Pleiades star cluster low in the west after dark in what should be a lovely sight to naked eyes and dazzling in binoculars.
As it passes in front of some of the stars, it might seem as if the huge Moon is swallowing the tiny stars.
Such occurrences provide excellent examples of how misleading appearances can be, especially regarding sizes and distances in the cosmos. It's easy to see how our ancient ancestors formed what we now know to be such wrong conceptions of the universe.
There's no question the sky looks big, and the Sun, Moon, stars and other night sky objects are far away. But only in recent decades have we come to realize just how big and how far away.
One of the largest appearing objects, the Moon, is really tiny with its 2,159-mile diameter being less than the width of the U.S. And orbiting Earth at an a average distance of only 239,000 miles, it's little more than an extension of Earth.
And while the Sun and Moon appear the same size, that too is deceiving. The Sun's diameter of 864,000 miles is 400 times that of the Moon (and over 100 times Earth's diameter). The Sun and Moon look of equal size because, by coincidence, the Sun's average distance of 93 million miles happens to be 400 times that of the Moon's average distance.
But even all these sizes and distances pale in comparison to those of the Pleiades. Each of those 100 or so "tiny" stars is a sun, many larger than our own. And their distance? How about 2.4 quadrillion miles (add 14 zeros!). Such a large number is so cumbersome astronomers use a unit of measure called a light year--the distance light travels in a year (5.9 trillion miles). So really the Pleiades are only 407 light years away--relatively nearby, cosmically speaking.
It quickly gets far more mind-boggling. Our Milky Way galaxy, 100,000 light years in diameter, is but one of countless billions of galaxies, most of which are thousands to millions of light years distant from each other. So while seeing the Moon graze the Pleiades is aesthetically beautiful, it gives no clue as to the true enormity of our universe.
- Next Two Weeks. Avg. sunrise: 7:04 a.m.; avg. sunset: 7:55 p.m. (for Waco, TX)
* The Moon is new today.
* Fri. evening the Moon is near Mars in the early evening, and pulls within one moonwidth before they set around 2 a.m.
* The Moon is at 1st quarter Apr. 12.
* The evening of Apr. 14 the Moon is to the right of Saturn, and the next evening to the planet's lower left with the slightly less bright star Regulus to the right.
- Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth's west-to-east rotation.) Evening: Mars is overhead with Saturn high in the southeast. Morning: Brilliant Venus hovers near the eastern horizon shortly before sunrise; Jupiter is the brightest object higher in the southeast.
- Eclipse Countdown. It's now only 16 years until the April 8, 2024, total eclipse of the Sun passes directly over the heart of Texas. Live healthily so you can join me in watching it.
- Astro Milestones. Apr. 12 is the 47th anniversary of Yuri Gagarin's 1961 historic 108-minute orbital flight around Earth--an early Space Age milestone. Astronauts now spend months in Earth orbit in the International Space Station.
March 22, 2008
Stargazer #475
Pirates' Eye Patch
Have you ever wondered why pirates are often shown with an eye patch? I've assumed the patch covered a damaged or missing eye, the result of their notoriously violent lives.
But recently a friend offered an another explanation. Perhaps the eye patch had to do with dark adaptation, something close to the hearts of stargazers.
Just as eyes automatically focus when viewing at different distances, they also adjust to the amount of light available. In bright light, our eyes' pupils partially close, allowing in less light, whereas in under low-light, the pupils open wide so more light can enter. In addition to the pupil responses, there are also changes in the retina--the part of the eye that receives the light--that help the eyes adjust.
We're familiar with this. When we walk into a dark movie theater it's often hard to find a seat until our eyes begin to adjust to the darkness. And when we leave, the brighter lights are often uncomfortable until our eyes adjust to the increased light.
Stargazers typically view very faint objects, so we want our eyes as dark adapted as we can get them. Under dark skies, our wide-open pupils and the changes in the retina make it easier to see the faint fuzzies we like to view. However, a second or two of bright light from a flashlight or auto headlight ruins night vision, making it impossible to see faint objects until our eyes readjust to the dark--something that can take several minutes.
Now back to the pirates. On ships where lighting was with candle lanterns, it was rather dark in the lower decks. After being below for a while their eyes would adapt to the low-light and they could see. But if they were to briefly go topside, the bright light would ruin their dark-adapted eyes, making it difficult to see when they went back below.
So, as the story goes, when going topside they covered one eye with a patch so that eye would still be dark adapted when they went back down.
According to my ophthalmologist, Dr. John Quinius, the story could be plausible. Our eyes' pupils normally react in tandem, so an eye patch wouldn't keep the covered eye's pupil opened wide. But changes in the retina occur individually, so the covered eye might conceivably remain more dark adapted.
Of course, if this was common practice, one would think all sailors of the day would have done it, yet I don't recall pictures of non-pirate sailors with eye patches. Whether true or fanciful, it makes for a good--and plausible--story.
- Next Two Weeks. Avg. sunrise: 7:21 a.m.; avg. sunset: 7:46 p.m. (for Waco, TX)
* Monday morning Venus is two moonwidths to the upper left of Mercury just above the eastern horizon 30-45 minutes before sunrise.
* The Moon is at 3rd quarter Mar. 29.
* The morning of Apr. 4 a thin crescent Moon is above Venus near the eastern horizon 30 minutes before sunrise.
- Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth's west-to-east rotation.)
Evening: Mars is high overhead with Saturn high in the southeast.
Morning: Venus and Mercury are near the eastern horizon 30 minutes before sunrise with Jupiter higher in the southeast.
- Star Party. The Central Texas Astronomical Society hosts its free monthly star party Mar. 29 at the Waco Wetlands beginning at 7:30 p.m. After an indoor program there will be a guided tour of the night sky and telescope viewing, weather permitting. For directions/map see my Website.
March 8, 2008
Stargazer #474
Why Is Easter So Early This Year?
If it seems like Easter comes early this year, you're right.
Based on the start of spring and the phase of the Moon, this
year's March 23 is almost as early as Easter can ever be.
Most holidays are fixed to a specific date, like Independence
Day on July 4 and Christmas on December 25. But two widely
celebrated holidays vary from year to year--Thanksgiving and
Easter.
Thanksgiving, a religious holiday in the minds of many, is
officially a civil holiday. It was originally a harvest festival
in what is now Canada in the late 1500s, and in what became
Massachusetts in the early 1600s. In some, but not all, of the
earliest years of U.S. history Thanksgiving was celebrated by
annual presidential proclamations through 1815.
Then there were none until President Lincoln resumed the holiday
as the last Thursday of November. In 1941, Congress and President
Franklin Roosevelt set the date as the fourth, rather than last,
Thursday in November, reportedly succumbing to pressures from the
business community to extend the time for Christmas shopping.
Easter, however, is a holiday of Christianity. It celebrates the
religion's foundational belief that following his execution,
Jesus briefly came back to Earthly life and then ascended into
heaven. In that this event was linked to the Jewish Passover, the
date for Easter was originally linked to Passover.
The date for Passover is based on the Hebrew lunisolar calendar
that regards both the solar (seasonal) year and the phases of the
Moon. Lunisolar calendars, which have been used by many cultures,
probably predate all modern religions.
So given its roots, it's not surprising that Easter is based on
a lunisolar calendar and linked to the spring season. No longer
tied to Passover, Easter is now celebrated on the first Sunday
following the full Moon which falls on or after March 21, the
symbolic first day of spring. (Astronomically, the first day of
spring varies from March 19-21.)
Unless the formula is modified, Easter will never fall earlier
than March 22 or later than April 25.
- Time Change. Tonight before retiring, set your clocks
forward 1 hour ("spring forward") from Standard to Daylight-
Saving Time.
- Next Two Weeks. Avg. sunrise: 7:39 a.m. CDT; avg.
sunset: 7:37 p.m. CDT. (for Waco, TX)
* Wednesday evening the Moon is above the Pleiades star cluster.
* Friday evening the 1st quarter Moon is to the right of Mars high overhead.
* The evening of Mar. 18 the Moon is above Saturn with the star Regulus between them, and the next
evening is below the planet.
* Mar. 19 is the spring (vernal) equinox, the first day of spring.
* The Mar. 21 full Moon is called Sap Moon and Crow Moon.
- Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth's west-to-east rotation.)
Evening: Mars is high overhead with Saturn well up in the east.
Morning: Brilliant Venus and Mercury are hovering near the east southeastern horizon at dawn while Jupiter is higher in the southeast and Saturn is setting in the west.
- Astro Milestones. Mar. 13 is the 227th anniversary of William Herschel's 1781 discovery of Uranus from Bath, England. Mar. 14 is the 129th birthday of Albert Einstein (1879-1955).
February 23, 2008
Stargazer #473
Happy Leap Day
Most of us seem to prefer it when things come out even. A Dollar Store has more appeal than a Ninety-Eight-and-One-Half Cent Store, and it makes more sense that a bottle of drink is 12 rather than 12.17 ounces. And wouldn't it be easier if they just said gasoline is $3 a gallon rather than $2.99.9? It just seems to simplify life a bit when things come out even.
Unfortunately, Mother Nature doesn't share that sentiment when it comes to time. Two of our more important measures of time are based on natural phenomena. A day is one rotation of Earth on its axis, and a year is one revolution of the Earth around the Sun.
If Mother Nature shared our compulsive need for orderliness, she would have made one year an exact number of days, but she didn't. In the time Earth revolves around the Sun (one year), our home planet rotates on its axis 365.2422 times, thus a year is a fraction short of 365 1/4 days.
Since our calendars (and minds) can't easily handle having a 1/4-day each year, we even it out by adding a whole day to the calendar every four years. By convention, we add that day to each year that is evenly divisible by 4. That day, Feb. 29, is called Leap Day, and the year is called Leap Year. In the U.S.,it's easy to remember as it coincides with presidential election years. So, next Friday will be Feb. 29, not Mar. 1.
When it comes to months, Mother Nature is even more untidy. It takes our Moon 29 1/2 days -- approximately one month ("moonth") -- to orbit Earth. Since we don't like fractions of days, we round a month to 30 days. But even that doesn't quite work as there aren't an even number of months in the year. So we add an extra day to some months -- except February which got short-changed.
See how messy all this is. Mother Nature could have been so much more orderly if she had Earth revolve around the Sun in exactly 360 days, and the Moon orbit Earth in exactly 30 days. Then those of us with compulsive tendencies could rest easier.
On the other hand, maybe a little disorder keeps life more interesting. In any case, happy Leap Day.
- Next Two Weeks. Avg. sunrise: 6:56 a.m.; avg. sunset: 6:27 p.m. (for Waco, TX)
* Wed. morning Mercury is 2 moonwidths above the much brighter Venus very low in the east southeast 45 minutes before sunrise.
* Thurs. morning the 3rd quarter Moon is to the right of the star Antares, and the next morning is to the star's lower left.
* The morning of Mar. 2, the crescent Moon is to the right of Jupiter low in the southeast, then the next morning is below the planet.
* The morning of Mar. 5 a thin crescent Moon is just to the lower right of Mercury with Venus to the lower left; all are within the same binocular field of view near the east southeastern horizon shortly before dawn.
* The Moon is new Mar. 7.
- Naked-eye Planets. Morning: Mercury and brilliant Venus are near the east southeastern horizon with bright Jupiter to their upper right; Saturn is setting in the west. Evening: Mars is high overhead as Saturn rises in the east.
- Star Party. The Central Texas Astronomical Society hosts its free monthly star party tonight at the Waco Wetlands beginning at 7 p.m. After an indoor program there will be a laser-pointer guided tour of the night sky and telescope viewing. For directions and map see my Website. (Canceled if raining.)
February 09, 2008
Stargazer #472
Total Eclipse of the Moon
Hope you got up early Feb. 1 to see Venus and Jupiter team up low in the east. The two brightest planets were dazzling, even if at an inconvenient hour. Now comes another show and at a much more agreeable time for most of us.
The evening of Feb. 20 will feature a total eclipse of the Moon over most of the western world, including the U.S. The earliest stage begins at 6:35 p.m. when subtle shadings of the Moon's surface become visible. Partial eclipse starts at 7:43 when the Moon begins entering the darkest part of Earth's shadow. The Moon becomes totally eclipsed at 9:01, reaching mid-eclipse at 9:30. It begins emerging from Earth's shadow at 9:52, with partial eclipse ending at 11:09, and the final stage ending at 12:17 a.m. You can't ask for better timing.
During totality, when the Moon is wholly within Earth's shadow, it will dim considerably, but it's not likely to disappear. Depending upon Earth's atmospheric conditions, the Moon will appear somewhere between a dark gray and a beautiful coppery orange. We won't know which until it happens.
Twice during each of the Moon's 29 1/2-day orbits around our planet, the Sun, Earth, and Moon align. At new Moon, the Moon is between Sun and Earth, and at full Moon, Earth is between the Sun and Moon.
If the alignments were exact, every new Moon would result in a total eclipse of the Sun with the Moon passing in front of the Sun, and every full Moon would cause a lunar eclipse with the Moon moving through Earth's shadow. But our Moon's orbit is a bit out-of-level with Earth's orbit around the Sun, so solar and lunar eclipses don't happen monthly. During most new Moons, the Moon passes just above or below the Sun's disk. And during most full Moons, the Moon passes just above or below Earth's shadow.
While total lunar eclipses aren't rare, they are infrequent. In the past 20 years our part of the world has seen fewer than a dozen good ones, most recently last August before dawn.
The next good one won't come until December 2010, and it happens after midnight, so let's hope for clear skies for time.
- Next Two Weeks. Avg. sunrise: 7:09 a.m.; avg. sunset: 6:16 p.m. (for Waco, TX)
* The Moon is at 1st quarter Wed.
* Fri. evening the Moon is near Mars and the star El Nath.
* The Feb. 20 full Moon is called Snow Moon, Hunger Moon and Wolf Moon.
* The morning of Feb. 21 the Moon is below Saturn and to the left of the star Regulus.
- Naked-eye Planets. (The Sun, Moon and planets rise in the east and set in the west due to Earth's west-to-east rotation.) Evening: Mars is high overhead as Saturn rises by 7:30. Morning: "Morning star" Venus and Jupiter are low in the southeast with Saturn the brightest object low in the west.
- Astro Milestones. Feb. 15 is the 444th birthday of Galileo Galilei (1564-1642). Feb. 18 is the 78th anniversary of Clyde Tombaugh's 1930 discovery of Pluto from Lowell Observatory in Flagstaff, Arizona. Feb. 19 is the 535th birthday of Nicolaus Copernicus (1473-1543).
January 26, 2008
Stargazer #471
The King and Queen Meet in the Morning
Friday morning (Feb. 1), Jupiter, the king of the sky gods, and Venus, the queen, pass breathtakingly close low in the east southeast as dawn begins to break.
If you're not a morning person, make this an exception as the sight will be worth getting up for. And if you are normally up and out in the mornings, you'll want to start watching now as the drama unfolds. Currently Venus, the brighter of the two, is above Jupiter, but each morning she coyly edges two moonwidths closer. When she catches him, she'll be just a moonwidth to his left.
But that's not all. Another piece of the drama is occurring further up as the crescent Moon is marching toward the couple at the pace of a moonstride each morning. (Hold your hand at arm's length while making a "hook 'em horns" sign; the distance between your extended fingers is a moonstride.)
The morning of the royal rendezvous, look for the crescent Moon to the right of Scorpius' brightest star, the reddish Antares, higher in the southeast.
But the show doesn't end Feb. 1. The morning of Feb. 3 a thin crescent Moon smiles down upon the pair from their upper right, and then the next morning is below them nearer the horizon.
Other than an occasional meteor or flaring satellite, the Moon, Venus, and Jupiter are the three brightest objects in the night sky. So when they all come together, it's a sight you won't want to miss.
Postscript: Readers with telescopes (or even binoculars) will want to zoom in on Jupiter as it is now two moonwidths to the left of a globular star cluster, M22. In binoculars M22 looks like a fuzzy out-of-focus star, larger but much fainter than Jupiter. Telescopes, however, begin to reveal its true nature.
Jupiter's dominating brightness gives the impression that M22 is one of his lesser subjects, but not so. At 400 million miles away (that's about 35 light-minutes), Jupiter is a next door neighbor compared to M22's distance of 10,000 light-years. Vastly more imposing than a mere planet, M22 contains a half million suns.
- Next Two Weeks. Avg. sunrise: 7:21 a.m.; avg. sunset: 6:04 p.m. (for Waco, TX)
* The Moon is at 3rd quarter Tuesday.
* Feb. 2 is Candlemas (and Groundhog Day), a cross-quarter day celebrating the middle of winter.
* The Moon is new Feb. 6.
- Naked-eye Planets.
Evening: Mercury is near the western horizon a half hour after sunset, Mars is high and bright in the east, and Saturn rises by 8:30 p.m.
Morning: Venus and Jupiter are low in the east as Saturn is mid way up in the west.
- Star Party. The Central Texas Astronomical Society hosts its free monthly star party tonight at the Waco Wetlands beginning at 7 p.m. After an indoor program there will be a laser-pointer guided tour of the night sky and telescope viewing. (Canceled if raining.) See MAPS & DIRECTIONS elsewhere in this website.
January 12, 2008
Stargazer #470
Looking Forward to 2008
Standing at the beginning of 2008, the Stargazer extends his best wishes to all. Hopefully, 2007 was good for you, and that the new year proves even better.
As always, we can count on Mother Nature to feed our souls with glimpses of her awesome beauty--if we take the time to notice. Here are some night-sky delights to touch our deeper selves.
The morning of Feb. 1, just before dawn, the queen and king of the heavens, Venus and Jupiter, pass within kissing distance of each other--right out in the open for all to see.
The evening of Feb. 20 features a total eclipse of the Moon visible over the entire U.S.
The evenings of May 21-23, reddish Mars passes in front of the beautiful Beehive star cluster, producing what should be a stunning sight in binoculars and small telescopes.
The evenings of July 5 and 6 see Saturn, Mars and the star Regulus closely aligned and joined by a crescent Moon.
This year's always-popular August Perseid meteor shower will be better in the morning than evening with the best show expected in the wee hours of Aug. 12 from 3 a.m. (when the Moon sets) until dawn. Other favorable 2008 meteor showers are likely to be the Eta Aquarids in May, the Delta Aquarids in July, the Draconids in October, the Taurids in November, and the Ursids in December.
The evening of Aug. 13 Venus passes within a moonwidth of Saturn, then the early evenings of September will display some interesting groupings of Venus, Mars, Mercury and the Moon.
The evening of Dec. 1, in what is likely to be the most dazzling celestial show of the year, the night-sky's three brightest objects--the Moon, Venus, and Jupiter--congregate after sunset.
And as we speak, the MESSENGER spacecraft, launched in 2004, is making its first flyby of Mercury. Skimming a mere 125 miles above the planet's surface on Jan. 14, it is imaging unseen parts of the innermost planet, so be watching the news for never-before-seen photos of our neighbor. Only somewhat larger than our Moon, Mercury is the least explored planet, other than the remote Pluto, so in 2011 MESSENGER will return and begin orbiting the tiny planet for more extensive study.
For Venus lovers--and who isn't--she continues as the "morning star" until mid spring, swings behind the Sun in June, then in mid summer emerges as the "evening star" for the rest of 2008.
The final thing to expect this year is the unexpected. While many night sky events are as predictable as the sunrise, we're often treated to surprises, like Comet Holmes which burst on the scene in October 2007, and is still faintly visible. So stay tuned and we'll do our best to keep you informed.
- Next Two Weeks. Avg. sunrise: 7:28 a.m.; avg. sunset: 5:51 p.m. (for Waco, TX)
* The Moon is at 1st quarter Tuesday.
* The evening of Jan. 19, the Moon is to the lower left of Mars which is to the lower right of the star El Nath high in the east.
* The Jan. 22 full Moon is called Old Moon and Moon After Yule.
* The evening of Jan. 24, the Moon is to the right of Saturn as they rise around 9 p.m.
- Naked-eye Planets. Evening: Mars dominates the high eastern sky with Saturn rising in mid evening. Mercury is becoming visible just above the western horizon at dusk and is at its best a few days before to a few days after Jan. 21. Morning: Venus is in the east with Saturn high in the southwest and Mars setting in the west.
