Friday, January 27, 2006

Star Notes or Highlights of the High Lights

The following posts are from my stint as the “Star Notes” columnist for the New Haven Register for a couple of years. I took a new departure, emphasizing naked-eye observing in an urban setting. This meant not only telling folks what's up there, but how to find it and why it's interesting.

Paradoxically enough, the light pollution we experience in an urban environment might actually be an aid to beginning to learn your way about the night sky. That is because only the brightest stars (and the planets and moon) will be visible, which form very recognizable patterns. Once you learn these, you can find everything else. I call these constant and readily recognizable denizens of the night sky “skymarks” – analogously to “landmarks.” (Any resemblance to my name is purely intentional.)

If you want to have this kind of information for every day of the year, two recommended sources are Chet Raymo's 365 Starry Nights (Prentice-Hall) and a subscription to the Abrams Planetarium Sky Calendar (Michigan State University, East Lansing, MI 48824). Those who wish to utilize telescopes are encouraged to take advantage of your local amateur society; in my area there are the excellent resources, both telescopic and human, of the Astronomical Society of New Haven. For extensive treatment of all things astronomical, check out the monthly periodicals Astronomy and Sky and Telescope. Finally, the best way to come to know the night sky is to learn the constellations, and the best possible introduction to the constellations is The Stars by H.A. Rey (yes, the Curious George creator!), published by Houghton Mifflin.

For a sample of my other writings on astronomy, click here.

I would like to thank Health and Science Editor Abram Katz at the New Haven Register for having given me my "start" as a columnist.

Clear skies! – Joel Marks

September 2, 1999

As night falls, look up! At the very top of the sky the first star you will see is Vega. This is the source of alien signals in Carl Sagan's science fiction classic, Contact.

One hour after sunset look low in the southwest, to the left of where the sun has set. There stretches the magnificent constellation Scorpio, the Scorpion. Three vertical, slightly bowed stars form its head, from which a long body and tail curve down to the left and then up again.

At the heart of this nocturnal arachnid is the red star Antares. This month you can see unmistakably why it has this name. Ares is the Greek name of the god the Romans called Mars. Hence Antares (anti-Ares) is the "Rival of Mars."

And, sure enough, the red planet Mars begins the month just to the right of Scorpio; at mid-month it is passing directly over Antares; and by next month it is as far to Antares' left as it is to its right tonight.

Later in the evening the brilliant planet Jupiter cannot be missed as it rises in the east. Dimmer Saturn rises after that; you can spot it easily after 10 p.m. on the 28th, clouds permitting, when it will lie midway between Jupiter and the Moon. The dazzling pre-dawn "star" in the east is the planet Venus.

At exactly 10:45 p.m. on the 29th, watch the bright star Aldebaran suddenly appear at the dark edge of the Moon's lower right side.

October 7, 1999

There are two "secrets" to finding your way about the night sky.

First, orient yourself. The astronomical way to do this is to find Polaris, the North Star, for it alone among the thousands of stars you can see stays in the same place, night after night, all night long.

One way to spot it is to locate the familiar Big Dipper, which at this time of year is large and low in the evening sky, its handle on the left and its cup facing up. If you follow an imaginary line up from the two stars that form the right side of the cup, the first star of comparable brightness your gaze will fall upon is Polaris.

Since New Haven is roughly halfway to the North Pole from the Equator, Polaris is roughly halfway up the sky from the horizon.

Now turn your back to Polaris so that you will be facing south. This is the part of the sky where most of the action happens. Each day the Sun, the Moon, the planets, and the stars of the Zodiac travel from your left, the east, to your right, the west.

The second key to stargazing is: Once you find something, hold onto it!

For example, this month reddish Mars is visible in the evening, low in the west. Later, as it sets, brilliant Jupiter rises in the east, with dimmer Saturn in tow one handspan to its lower left. (A handspan is the spread between the pointer and little fingers of an adult hand at arm's length.)

Jupiter and Saturn will rise earlier each day, but Mars keeps pretty much to its same schedule. Hence the former will overtake the latter, so that by April they will all come together in the west in an amazing conjunction.

November 4, 1999

Meteor alert! The annual Leonid shower returns on the night of November 17-18, and it just could be the display of a lifetime.

Since the Earth is now well positioned relative to Comet Tempel-Tuttle, whose debris constitute the "shooting stars" we see, some astronomers predict a maximum rate of 1000 meteors per hour.

Mars, the next planet out from the Earth, continues to shine in the west after sunset: Identify it by its reddish tint.

Beyond Mars lies giant Jupiter, which is currently the brightest object in the evening sky, save the Moon. You will find it rising in the east as darkness falls and crossing the sky all night.

Next in line is Saturn, the bright object to Jupiter's lower left. On the 22nd it sits midway between Jupiter and the full Moon.

Two striking star clusters lie to Saturn's lower left. Look for the fuzzy glow of the Pleiades and, below them, the Hyades' wedge (a "V" on its side, pointing right).

Venus, the next planet in from the Earth and the brightest "star" of all, dominates the pre-dawn sky as it rises in the east ahead of the Sun. Venus is nicely complemented by Jupiter, which by this hour is setting in the west.

Finally, the innermost planet, Mercury, puts on a rare show just before sunset on the 15th, when it passes directly in front of the Sun. However, to know exactly where and how to look and, most importantly, to protect your eyes from the Sun's glare, you must team up with an expert if you are going to attempt to watch this event. The Astronomical Society of New Haven is planning a special observing session to see it; for more information, contact the Society.

December 2, 1999

How many dippers can you see in the sky? Most people know the Big Dipper, which is currently low in the north after dark. Then there's the dim Little Dipper, hanging like a pendant from Polaris, the North Star.

But on December evenings you can also see a littler dipper and a bigger dipper!

To find them, turn around and face south. Dominating the stars will be the planet Jupiter, with Saturn a handspan to its left. Now scan further to the left until you notice a glowing patch a little higher in the sky. That's the Pleiades.

If you look closely, you will see their glow resolve into a cluster of six stars, even though they are named after the Seven Sisters of antiquity. And even though we might also expect a dipper to contain seven stars, this cluster does in fact look like a tiny dipper.

Now look to the upper right of Jupiter, where you will see the Great Square of Pegasus, or the "cup" of the biggest dipper of all. These four stars are all a handspan apart. The "handle" is a line from the upper left star to three more equally bright and equally separated stars bridging overhead, traversing the constellation Andromeda and ending in Perseus.

Tomorrow morning the waning crescent Moon hovers above blazing Venus. Just before dawn on the 5th locate elusive Mercury directly below an even thinner crescent. Finally, find reddish Mars immediately to the right of the waxing crescent on the evening of December 12.

By the 22nd the Moon is full; furthermore, by chance, the Moon will be at its closest approach to Earth and this is also the winter solstice. Therefore Diana will dazzle us with her especial brilliance during the longest night of the year.

January 6, 2000

A total eclipse of the moon tops the night of January 20-21. At 10 p.m. the moon first enters the earth’s umbral shadow, with totality lasting from approximately 11 p.m. until 12:30 a.m. Here are some interesting things to watch for.

The moon is always moving in opposite directions at once: from east to west in its apparent motion, due to earth’s rotation, and from west to east, which is its physical motion in orbit around the earth. Normally we are only aware of the former. But during an eclipse, we can vividly observe the latter as the moon crosses the earth’s shadow projected into space. Thus, you will see the left edge of the moon darken first.

The relative sizes of the moon and the earth also become apparent. Consider that the moon’s diameter is 2160 miles, and the earth’s 7928; therefore the moon must travel approximately four times its own width through the disk of the earth’s shadow. Using you knowledge of the moon’s mean distance of 239,000 miles, and simple geometry, you can then roughly calculate the eclipse’s duration, and confirm it with your own eyes.

Because some sunlight still reaches the moon from bending by the earth’s atmosphere, the moon is likely to appear deep red during the totality. It could also have a bright southern tip, making it look like a science fiction image of Mars with its polar cap.

Find the real Mars just to the right of the waxing crescent moon one hour after sunset on the 10th.

The moon passes below Jupiter on the 14th and Saturn on the 15th. A waning crescent moon almost “touches” brilliant Venus at dawn on February 2nd.

February 3, 2000

Not until 2002 will you be able to see more bright stars and planets all at once than are visible in this month's evening sky.

The highlight of every winter sky is the constellation of Orion, the mighty hunter. He has been striding up from behind the eastern horizon since September, and this month stands due south by 8 p.m.

His distinctive belt of three stars -- Alnitak, Alnilam, and Mintaka -- slants from lower left to upper right. To their upper left is his raised right shoulder: the beaming red star Betelgeuse. Continue clockwise to his left shoulder, Bellatrix, left knee, Rigel, and right knee, Saiph.

Suspended from Orion's belt is his scabbard. Its middle "star" is in fact a nebula, where new stars and even planets are being born.

The large tilted trapezoid to Orion's lower left is his trusty hunting dog, Canis Major. His dog tag is Sirius, the brightest star in the sky except for the sun.

Continuing in a ring around Orion: The brightest star to his east is Procyon, in Canis Minor. Further up are the Gemini "twins": Pollux, the brighter, and Castor. At the zenith is Capella, in Auriga.

Swinging back down to Orion's upper right, you will find reddish Aldebaran in the V-shaped head of Taurus, the bull.

Now follow a line to the western horizon, along which the four brightest objects will be the planets Saturn, Jupiter (brighter even than Sirius), Mars, and, finally, Mercury (at dusk in the first half of February, and paired with the Moon on the 6th).

March 2, 2000

Watch the western skies this month for a lovely pas de quatre among the Moon, Mars, Jupiter, and Saturn.

The dance begins about one hour after sunset. The three planets are arrayed in a diagonal line plunging towards the western horizon, with Mars the lowest and Saturn the highest. Between them is Jupiter, which, at the start of the month, is the brightest object in the whole sky.

On the 7th, the waxing crescent Moon joins the planetary trio. At first it appears on the horizon below them all, but on succeeding evenings it glides by each planet in turn as the Moon pursues its easterly orbit around yet another planet, Earth. By the 10th, the Moon has become the highest of the four members of the lunar-planetary alignment.

Meanwhile, the planets are converging at a rapid clip, and actually display four types of motion simultaneously. First, each night all three planets set in the west because of the easterly rotation of the Earth. Second, all three planets are lower each night due to the Earth's revolving around the Sun more rapidly than they. Third, they are moving eastward against the background stars in their orbits around the Sun. Fourth, they appear to be approaching one another because of their own relative orbital speeds.

The vernal equinox returns at 2:35 a.m. on the 20th. On this date the Sun rises due east and sets due west. By coincidence, the Moon will also rise due east that same evening. This is a good month to get oriented!

April 6, 2000

We have been following the planets Mars, Jupiter, and Saturn since September. This month their nocturnal progress culminates in a splendid conjunction, the likes of which have not been seen since the first year of the 20th century, nor will be seen again until the latter part of the 21st century.

On opposite sides of the sky last fall, the two gas giants are now in the same part of the sky as the red planet, low in the west one hour after sunset. They can all be readily identified tonight due to the placement of a sliver crescent moon, with which they form a lovely quadrilateral.

Saturn is the brightest “star” to the right of the moon, while to their lower right, brilliant Jupiter pairs off with reddish Mars.

Watch for the internal motions among the planets. Saturn and Jupiter continue to close the gap between them, while Mars travels across the gap, reaching midpoint on the 11th and ending the month above the others.

The most compact grouping occurs on the 15th, which, fortuitously, is just before Jupiter and Saturn become too low to be easily seen.

Meanwhile, two stellar animals dominate the evening sky overhead. Just to the south of the zenith lies Leo the Lion, his head to the right, forming a backward question mark. Just to the north of the zenith lies Ursa Major, the Big Bear, best known for the prominent asterism she contains, the Big Dipper.

May 4, 2000

Today and tomorrow all seven classic planets will be bunched together in a rare conjunction. So why will you only be able to see three at most?

The catch is that the “classic planets” include the Sun. Therefore, when all of them are together, the others are close to the Sun in broad daylight and so cannot be seen.

At least not until the Sun is below the horizon, when the outermost of the grouping may straggle sufficiently to be visible just before they set in turn. Thus, a clear view of the westnorthwest in tomorrow’s evening twilight will reveal a thin crescent Moon (beside a bright star) and, to the lower right, faint red Mars. Binoculars are advised.

Why was the Sun originally counted among the planets? The Greek word from which our word “planet” is derived means wanderer, so the Sun, and also the Moon, were grouped with Mercury, Venus, Mars, Jupiter, and Saturn as the only naked-eye “stars” to move among the other, “fixed” stars.

After the fall and winter spectacle of converging planets, the night sky is peculiarly bare this month. So this is a good time to locate the three bright stars of spring.

Arc to Arcturus by extending in imagination the curve of the Big Dipper’s handle from its tip one Dipper-length in the direction away from the cup. Continue the arc a similar distance to Spica. The Moon crosses from right to left of Regulus on the 10th and 11th.

June 1, 2000

On June 20 the sun will set in New Haven at 8:28 p.m. One hour and twenty minutes later, it will have climbed to the top of the sky over the Tropic of Cancer, thereby marking the beginning of summer in the northern hemisphere.

Along with the longest day (including longest twilights) of the year comes the shortest night of the year, which is just as well because there's not much happening up there this month for the evening naked-eye urban skygazer to see!

One hour after sunset on Saturday, however, you should be able to find Mercury low in the west-northwest just to the upper right of a thin crescent moon.

Meantime in the morning, preparations are being set for evening events to come. An hour before sunrise on the 13th, Jupiter and Saturn will form a striking pair low in the east-northeast. They are now at their closest to each other in the sky for the next twenty years.

When last visible, Jupiter and Saturn were in the western sky, setting just after the sun. We had been watching them since autumn as they rose and set earlier each month, dominating the evening sky. That process continues, shifting them now into the morning sky. They will then do another round of the sky before disappearing again next May.

There is a slight possibility of a meteor shower in the early evening of the 26th. Look for slow-moving streaks seeming to emanate from directly overhead.

July 6, 2000

This is a month for stretching your eyesight and your imagination.

The giant planet Uranus is now approaching opposition, which is when a solar system object is due south in the sky at (true) midnight. Thus, it is "opposite" or face-on to the Sun from Earth's position and also closest to us, hence at its brightest.

At this time Uranus is actually visible without optical aid, provided the seeing conditions are ideal. Most likely you will require binoculars, and you will definitely need a detailed star map. The folks at the Astronomical Society of New Haven will be happy to show you the planet at one of their public observing sessions this summer. While you're at it, check out Neptune and Pluto through a telescope!

Meantime, in the same part of the sky you can also spy Vesta, the third-largest asteroid at a whopping 510 km diameter. Although very faint, it is now brighter than Uranus because it is much closer. But don't worry; it keeps its distance, orbiting the Sun beyond Mars like the little planet it is.

All of these planets are clustered near the glorious summer constellations of Scorpius, the scorpion, and Sagittarius, the archer (who also bears a remarkable resemblance to a teapot!). Let the Moon guide your fancy as it courses leftward over these denizens of the Zodiac from the 11th to the 15th.

August 3, 2000

With no planetary diversions of evening viewing, this is an ideal month to observe the galaxy in which we live. The Milky Way spans the sky from east of north to west of south, passing overhead by midnight.

It seems that most urban dwellers have never seen this spectacle, which is a tragedy. There it is, right above our heads: one of nature's wonders. Yet even when the sky is clear of clouds and moonlight, pollution from artificial illumination wipes out the night just as surely as sunlight.

So you will have to travel into the countryside to spy the dark sky; but then all you will need is your naked eye.

What you will notice is a nebulous and patchy pale white swath. What you are actually seeing, as Galileo was the first to glimpse through a telescope, is a collection of countless stars.

The reason the stars are so bunched together along this band is that our galaxy is flattened like a disk. Thus, when we look along the plane of the disk we see the most stars. The individual stars we see in the rest of the sky are fewer and closer because they only populate the relatively thin width of the disk in our vicinity.

In fact, if you face the Teapot asterism -- low in the south after dusk -- you are peering into the center of the galactic disk, its densest part.

Locate the Teapot on the 10th: slightly tilted, handle on the left, spout on the right, lid directly below the Moon. Then head out into the country two weeks later, after the Moon has vacated the premises, leaving the Milky Way's glow unrivaled.

September 7, 2000

This month is for the birds: Cygnus the swan and Aquila the eagle, to be exact. These beautiful constellations fly above our heads in the evening, accompanying their migrating counterparts here below.

There's a bit of confusion up above, however, because the heavenly flappers are flying in opposite directions. Actually, they are more like English lorries nearly on a collision course as they barrel down the left sides of a narrow country lane, in this case, the Milky Way.

Deneb, the Swan's tail, and Altair, the Eagle's eye, form a large triangle of bright stars with Vega, which is located directly overhead just as darkness descends. Vega is the brightest of the three and probably the first of all stars you will see at dusk. If you are facing south, Deneb is to the upper left of Vega, and Altair to the lower left.

Now use your imagination to fill in the rest of the birds. The Swan's magnificent wingspan arcs gracefully back, while the Eagle's wings reach forward, like a diving bat's. The inner part of the Swan's wings also form the transverse beam of the Northern Cross.

By midnight on the 17th, Jupiter, Saturn, and the Moon form a line slanting up from the left. Watch the progression all night.

The Harvest Moon blazes on the 13th. Autumn arrives at 1:28 p.m. on the 22nd.

October 5, 2000

There is no excuse not to stargaze this month, as the dark of evening becomes inescapable, for better or worse, even as you leave your work place. The sun sets almost two hours earlier by the end of October than at the beginning, thanks both to the seasonal shortening of the days and to the return of Standard Time on the 29th.

The big show is provided by the giant planets, Jupiter and Saturn. They are visible as both morning and evening "stars," rising in the east a few hours after sunset and still shining in the southwest before dawn.

Jupiter is the scene-stealer, best seen blazing in the southeast before midnight. Saturn is then to its upper right.

If you're not sure of their identification, watch the moon play roulette with them. On the 15th the moon will be just to the right of Saturn; on the 16th it will be just below Jupiter, and also to the left of the bright, reddish star Aldebaran, which forms a striking isosceles triangle with the planets all month.

In fact, these three will dance with one another right through to spring, so keep watching!

A lovely sight at dusk on the 30th will be the crescent moon, bright Venus, and red Antares, all in a line sinking into the southwest.

Witches won't be able to navigate by the full moon this Hallowe'en, as the new moon comes on the 27th.

November 2, 2000

Gone are the planet-bereft skies of last summer. The three brightest planets -- Venus, Jupiter, and Saturn -- are now on brilliant display. The first is setting in the west after dusk while the two latter are simultaneously rising in the east.

Venus has no rival, so there's no missing it. One hour after sunset on the 19th, it will form a beautiful pair with the waxing crescent moon.

Jupiter similarly dominates its corner of the sky, shining to the lower left of Saturn as night falls. In their vicinity are two outstanding star clusters, the lovely, glittering Pleiades to the upper left, and the ">" (or lying-down "V") of the Hyades to the lower right, the latter highlighted by the bright reddish star Aldebaran. Together these planets and clusters form an enchanting, bejeweled cat's cradle, changing shape with the passage of the cold, dark months.

If we consider not the spectacle of the night sky but its wonder, there is no more remarkable object in view, now or ever, than a tiny smudge that is optimally placed at the very top of the sky at 9 p.m. later this month: the Great Andromeda Galaxy. At 2.3 million light-years' distance, it is the furthest object visible to the naked eye.

The Leonid meteor shower will return on the mornings of the 17th and 18th. Expect about one meteor per minute at
around 3 a.m.

December 7, 2000

At mid-day on Christmas, the Moon will partially eclipse the Sun. Is this a fond farewell to the Twentieth Century, or a hale hello to the Twenty-First? Take your pick: At peak eclipse, the Sun will be half covered, or half-uncovered, as you prefer!

Never look at the Sun unless you use a filter of which you are certain, since you can permanently damage your eyes even when the Sun is eclipsed or behind a cloud. Pick up a piece of #13 or #14 welder's glass at any welding supply store. Special solar viewers are available from reputable optics suppliers; consult Even with a filter, do not stare; only glance.

The safest way to view the Moon taking a bite out of the Sun is via projection through a pinhole in a south-facing window shade onto a white surface. The eclipse begins at 11:15 a.m., with maximum at 12:45 p.m.

Meanwhile, the nighttime is aglow with marvels. The brightest evening "star" in the southeast is Jupiter. Tonight it is smack-dab between the glittery Pleiades above and reddish Aldebaran below. Saturn is to the right of the Pleiades.

Mighty Orion strides over the eastern horizon as night falls, bringing winter with him, which officially begins at 8:37 a.m. on the 21st.

The brightest evening "star" in the whole sky is Venus, setting in the southwest. Don't miss its pairing with a crescent Moon on the 29th.

January 4, 2001

A little waltz music, please! Just in time for 2001, Space Station Alpha becomes visible in the evening and predawn skies.

This is the largest and brightest human-made object in space, and is outshone only by the moon and Venus among natural nighttime objects. At an altitude of 250 miles, its giant energy-generating solar panels reflect sunlight that is streaming up from just below the horizon.

Meanwhile, Venus is so bright this winter that it can be seen during daylight, so that spot in your eye might just be a planet. After dusk there’s no missing it as it blazes in the southwest.

Complementing Venus in the southeast are bright Jupiter and Saturn. This evening all three planets form an arc that spans exactly 90 degrees, or one half of the sky.

Just below Jupiter is the bright reddish star Aldebaran. To its lower left in turn is the bright reddish star Betelgeuse, the eastward shoulder of the great winter constellation of Orion.

Today the Earth is at its closest approach to the Sun of the whole year. So why is it winter for us? For the same reason that it’s summer in Brazil: The tilt of the Earth on its axis.

February 1, 2001

This month's Star Notes is dedicated to our new president, whose lowest grade at Yale was in astronomy.

Were George W. to look up in the early evening this month, he would see the winter sky in all its glory. Magnificent Orion, with his distinctive three-star belt, stands tall in the middle of the southern sky.

Circling him from lower left are Sirius, the brightest star in the whole sky, then Procyon, then Pollux and Castor, then Capella, which is at the zenith, and finally Aldebaran, whose reddish tint sets it off nicely from brilliant Jupiter to its upper right.

Now let us peal the onion of Orion, for there is also an inner layer of bright stars. These are, if you will, his shoulders and knees, above and below his luminous belt. The most prominent are Betelgeuse to the upper left and Rigel to the lower right.

Tonight, the first of February, Jupiter, Saturn, and the moon are all in a line. They put in a repeat performance on the last day of February as well.

Meanwhile, Venus not only is a beacon in the west all month for a few hours after sunset, but also can be seen in full daylight in the afternoon, a quarter of the sky to the left of the sun.

March 1, 2001

Hesperus is Phosphorus: The Evening Star is the Morning Star. And so you shall see at the end of this month, as you watch the blazing planet Venus sink into the west behind the setting Sun, but rise in the east in advance of the morning Sun.

How can this be? The main reason is that the inner planet is moving more quickly than we are in our respective orbits around the Sun, thereby changing the relative geometric orientations of the three bodies. Additionally, Venus is currently above the Sun from our point of view, so, like the mast of a ship, the one precedes the appearance of the other and then follows its disappearance.

Since Venus is also approaching a point in its orbit where it stands between the Sun and us, it is coming closer to the Earth and, hence, increasing in angular size in our sky. Another consequence is that Venus is now exhibiting a crescent phase. The combined result is that by midmonth it should be possible to detect the curved shape of Venus’s cloud-covered disc with binoculars, and perhaps even the naked eye.

Spring arrives at 8:31 a.m. on the 20th. A sure sign is that Leo the lion is leaping up from the eastern horizon, no doubt in karmic pursuit of Orion the hunter, who has been pursuing Taurus the bull all winter.

Watch for a gorgeous conjunction of reddish Aldebaran, crescent moon, and brilliant Jupiter on the 29th.

April 5, 2001

All fall and winter we watched the planets Jupiter and Saturn move across the sky from east to west. And yet they stayed in the same place.

These largest gas giants have been in the constellation Taurus the Bull all along. That is because they are so distant from the Sun, their orbits take about 12 and 30 years, respectively. If you consider that their paths in the sky pass through the twelve constellations of the Zodiac, it makes sense that they would remain in each one for at least a year.

Of course it is a coincidence that Jupiter and Saturn are in Taurus at the same time. This is when they provide the special visual treat of dancing do-si-do with the finest star clusters in our skies, for both the V-shaped Hyades and the glittery Pleiades are in Taurus.

There being twelve Zodiacal constellations, which appear to circuit the globe annually (mimicking what the Sun does daily), we can expect each one to move from east to west in approximately two seasons. And so that is why Jupiter and Saturn in Taurus are now doing their swan song in spring, falling into the western horizon shortly after sunset.

Watch the waxing crescent Moon join the group on the 25th, halfway between Saturn and the reddish star Aldebaran.

May 3, 2001

Just a couple of months ago the stars beckoned while we ate dinner. But the switch to Daylight Saving Time, and the longer days and longer twilights of spring are conspiring to restrict the night, so the celestial scene begins to belong to insomniacs and children's dreams.

The Big Dipper is the guide to May's highlight high lights. Find it near the top of the sky. If you are facing south, then it will be over the top, so you'll be craning back a bit. From this orientation the Dipper is right-side-up, with the handle on the left.

Now follow that handle down to the left with your eyes, and you will "arc to Arcturus," the brightest star of spring. It's orange.

Continue the arc an equal distance, and you will arrive at Spica, the brightest star in Virgo.

Complete the circle back to the Dipper and you will pass leaping Leo the lion, with the bright star Regulus at the bottom of a reverse question mark.

Meantime, May's highlight low lights are the planets Mars and Venus. Although relatively low in altitude, they are high in brilliance.

Venus is the Morning Star, in the east before dawn.

But it is Mars that busts the evening brightness records, outshining everything but the Moon. Look for the red "star" rising in the east around midnight tonight, and earlier thereafter.

Thursday, January 19, 2006

June 7, 2001

Mars dominates the evening sky this spring and summer. At its brightest since 1988, the ruddy planet cannot be missed as it ascends after sunset in the southeast. Not even the star Antares, of similar hue and close on the right, can presently live up to its name of "rival of Mars."

The cause of this phenomenon is the coincidence of Mars' near approach to both the Earth and the Sun. Because Mars' orbit is relatively eccentric, its distance from the Sun varies over tens of millions of miles. Meantime, Mars' distance from the Earth varies over a much greater range, as the latter, being closer to the Sun, speeds ahead to the other side of our star and then comes round again from behind. As a result, every 16 years on average these two values reach a minimum at the same time. Then Mars presents a bigger disk in our sky, hence reflecting more sunlight into our eyes.

Another coincidence is that Mars is changing seasons just as we are, although our northern hemisphere is heading into summer (on June 21) while our neighbor's is leaving it (on June 17). The occasion is particularly serendipitous for telescopic observers during this close apparition, since, on Mars as on Earth, the beginning of fall is a point in a planet's orbit when its entire surface, including both poles, is illuminated for half the day.