In the Sky Tonight
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Wednesday, August 24, 2005
Looking High in the East-Southeast in Late Evening
We get many questions from people in northern latitudes about if and when they can view the Southern Cross asterism in their portion of the sky. The truth is that unless you live close to the equator (Hawaii, or the southernmost parts of Texas or Florida for those of us in the U.S.), you will not be able to view this famous asterism, also known as the constellation Crux.
Take heart, however, for we in the northern half of the globe have its less renowned, but elegantly beautiful cousin in our skies tonight. The star Deneb on today's chart identifies the top of the astronomical grouping called the Northern Cross, and the star Albireo marks the bottom. Unlike its southern counterpart, the Northern Cross asterism is a clipped version of another constellation Cygnus the Swan. Tonight you can find this constellation high in the east-southeast in late evening.
As an added bonus, if you have a pair of binoculars, I suggest you break them out this evening and point them at this constellation. Around the Swan is a part of our Milky Way galaxy that is called the Cygnus Star Cloud. It is part of the spiral arm of our galaxy that also contains our sun, and you should be able to pick out stars from it if it is a clear night in your area!
By the way, you can find the planet Mars rising in the east-northeast in late evening now. -
oh wat a pityOriginally posted by poon cho tang:these few days raining or cloudy
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Thursday, August 25, 2005
Looking East-Northeast at Midnight
Friday, August 26, 2005
Looking East-Northeast at Midnight
The chart on top shows you the east-northeastern sky at about midnight this morning. The waning gibbous moon was located about six degrees to the upper left of a bright reddish object -- the planet Mars.
Not far from this pairing to the lower left, you may have seen a noticeable star pattern, one of the most recognizable objects in the night sky. It's the Pleiades (M45), or Seven Sisters, an actual cluster in space whose member stars are bound by gravity. The Pleiades appears to the eye as a tiny dipper, wrapped in a veil of mist.
Despite the name Seven Sisters, many people see this cluster with the eye alone as six stars. Thus there are legends explaining the whereabouts of the "lost Pleiad." But people have different abilities to see faint stars. It's said that as many as 18 stars may be seen with the eye alone if your sky is exceptionally dark and clear . . . Binoculars will show you more stars, too, and a small telescope will reveal 40 or 50 stars (although the cluster is so large that you might get the best view of it through your telescope's finderscope).
Professional astronomers have counted more than 200 stars here. The cluster lies some 400 light-years away. Most stars in the Pleiades occupy a volume of space about eight light-years across. The misty look to the Pleiades is actually gas floating in space between these stars.
Throughout history, and in the lore of many nations, the Pleiades have had their own special mystery. This beautiful sky object has been compared to a swarm of fireflies or bees, to seven maidens, to a flock of doves, and to a hen surrounded by her chicks.
The bottom chart shows the positions of these objects on midnight of tomorrow morning, the 26th, when the moon will then be located less than a degree to the right of M45. The moon will appear to occult, or pass in front of, some of the stars in this cluster several times over the next year. -
i can see these 3 'stars' clearly toniteOriginally posted by BabyLover:oh wat a pity
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Saturday, August 27, 2005
Looking West-Southwest After Sunset
A skywatcher from Virginia asks, "How can I tell the difference between stars and planets when looking into the sky at night?" Well, we can take a few tips from our ancient astronomers.
When our ancestors looked into the skies, one thing that they noticed was that most bright objects in the sky travel in fixed positions with relation to each other, while a few bright objects did not seem to follow this pattern. The ancients took the "fixed objects" and grouped them into constellations, whose movements were so regular and reliable that these groupings helped them find their way on the ocean, on land, and even helped them predict annual events like floods and harvests.
If you were to look at the sky night after night, you would notice the same thing. Stars will appear in fixed positions; think about how constellations retain their familiar shapes but still move across our sky.
Planets, on the other hand, move in much more complex paths with respect to stars. Sometimes they even appear to move backwards in our sky, in an event known as retrograde. So, it'll take a little practice -- and some patience -- but if you can track the movement of objects in the sky for several nights in a row, you will be able to tell which are stars and planets by the movements that they make relative to each other in the sky.
Another way of telling planets apart from stars is that stars appear to twinkle in the sky, and planets generally do not. And so your homework assignment for tonight is to spot the planets Venus and Jupiter and the star Spica up in the west-southwestern sky, and see if you can tell them apart just by seeing which one twinkles.
I know, I know...Venus is way easy to recognize using the chart vs. Spica, but the idea is to see what "twinkling" looks like vs. "not twinkling" so you can apply it to less obvious situations. Like perhaps the one going on in the predawn east-southeastern horizon.
See if you can tell the difference between the planet Saturn and the star Procyon, who have much more similar magnitudes than Venus and Spica. By the way, you can also find the planet Mars high up in the eas-southeast before dawn. -
September - October mornings, 2005
Looking East Before Sunrise
A skywatcher from New Jersey writes: "What is the zodiacal light?"
The zodiacal light looks like a hazy pyramid of light extending up from the horizon, seen when all traces of twilight have left the evening sky . . . or before twilight begins in the morning. It's best seen in the evening from late February through about April or May. And you're most likely to see it before dawn from now through about October or November.
When it's visible in the morning, the zodiacal light is sometimes called "the false dawn." This light can be extremely bright and easy to see from latitudes like those in the southern U.S. Sometimes, highway drivers mistake the zodiacal light for the lights of a city or town just over the horizon.
Meanwhile, skywatchers in the northern U.S. or Canada sometimes say, wistfully, that they've never seen it. So, you might have to travel south of New Jersey to see the zodiacal light. And you'll also need a dark sky location to see it, someplace where city lights aren't obscuring the natural lights in the sky.
The zodiacal light is even "milkier" in appearance than the Milky Way. It's most visible before dawn at this time of year because -- as seen from this hemisphere -- the ecliptic stands nearly straight up with respect to the eastern horizon before dawn now.
We've marked the ecliptic as a pink line on today's chart. This is the view about two hours before sunrise. The zodiacal light can be seen for up to an hour before true dawn begins to break. Unlike true dawn, though, there's no rosy color to the zodiacal light. The reddish skies at dawn and dusk are caused by Earth's atmosphere, and the zodiacal light originates far outside our atmosphere.
The ecliptic (the pink line on our chart today) represents the edgewise view into our own solar system. The zodiacal light is actually sunlight reflecting off dust particles that move in the same plane as Earth and the other planets orbiting our sun. -
Tuesday, August 30, 2005
Looking East-Northeast 1-2 Hours Before Dawn
Today's chart is aimed east-northeast about an hour before sunrise. That's where you'll find two bright stars flanking the waning crescent moon. Even when the moon has moved on, these stars are noticeable for being bright, yet close together on the sky's dome. They are Castor and Pollux, and they're the brightest lights in the constellation Gemini the Twins. The stars themselves are often referred to as "twins," but they're not really connected in any way.
Castor's estimated distance is 52 light-years, while Pollux is estimated to be 34 light-years away. In other words, these two stars are about 18 light-years apart . . . more than four times farther apart than our sun and its nearest neighbor, Alpha Centauri. To the eye, Pollux shines with a golden color, while Castor is blue-white. There's a marvelous description of Castor in the great book Turn Left at Orion by Guy Consolmagno and Dan M. Davis.
A small telescope would show the single point of light we see as Castor to be two stars of similar brightness, with a third fainter star some distance away. The two primary stars are known as "A" and "B." Each one is also a double star. All four stars in the A and B pairs are hot and young, roughly twice the size of our sun and 10 times as bright.
What's more, the stars in each pair orbit very closely, separated by just two or three star-diameters. Because they're so close, each pair of stars spins around its common center of gravity very quickly! The A pair completes its mutual orbit in only nine days. The B pair orbits in only three days. That's in contrast to our Earth's orbit around the sun of 365 days.
But don't forget the third fainter star, orbiting some distance from the other two. Star "C" is also really two stars, which orbit each other in less than a day. By the way, the C pair is pursuing a long orbit indeed around the A and B pairs. The C stars need 10,000 years to go around their brother stars. And remember, although we're talking about a total of six stars in the A,B and C pairs . . . all six stars reside in the single starry point we know as Castor.
By the way, there's another starry point below the moon and twins that you won't want to overlook. It looks like a star . . . but it's really the planet Saturn, which now lies low on the horizon. -
Wednesday, August 31, 2005
Looking West-Southwest After Sunset
Thursday, September 1, 2005
Looking East-Northeast Before Sunrise
If you look at the chart on the left (which represents this evening's west-southwestern sky after sunset), a scant one-and-a-half degrees separates the planets Venus and Jupiter now. Tomorrow evening, they squeeze even tighter still -- culminating in the closest grouping of Venus and Jupiter in our sky for the year. Tomorrow (at the same time and direction of sky) these two planets will squeeze to less than a degree apart in our sky.
Astronomers have a term for such planetary groupings which appear, from Earth, to come close to one another but do not actually occult (or pass in front of) one another. This phenomenon is termed an appulse and is not limited to planetary groupings, but also encompasses all other kinds of objects in the celestial sphere.
We have gotten many comments from skywatchers about Venus being so incredibly big and bright. Indeed - Venus is the brightest object in our night sky, after the moon. As you look at Jupiter, seeming to rest on top of Venus, this evening think about the relative sizes of these planets to one another. If you take into consideration that Venus is almost as big as Earth (being about 95% it's diameter) and that about 1000 planet Earths could fit inside a hollowed out planet Jupiter, then it seems almost incredulous that Venus should appear so bright and large in our sky, while the giant planet Jupiter is small in comparison. However, Venus is much, much closer -- a resounding 340 million miles closer! At that distance, our sister planet outranks the giant Jupiter in appearance.
For those of you up in the early hours before sunrise, it may be one of your last chances to catch Mercury before it gets lost in the glare of the morning sun. -
Thursday, September 1, 2005
Looking East-Southeast One Hour After Sunset
A skywatcher wrote, “When will Uranus be visible?” It’s visible now. Actually, it’s visible for most of every year, as all the planets are. The planets in our solar system aren’t visible when they’re located in the same direction as the sun. Otherwise, they’re in our sky for some portion of every night.
The outer planets (Jupiter, Saturn, Uranus, Neptune and Pluto) come to a location in our sky each year called “opposition” by astronomers. That’s when Earth has come between an outer planet and the sun. At such times, the planet rises in the east while the sun is setting in the west. It appears in our sky all night long.
Opposition is the middle of the best time of year to see a planet. But perhaps the most convenient time for seeing a planet comes within the month or so after opposition. Then the planet is already up in the east to southeast at sunset, in a convenient place for evening viewing. Now . . .about that word “visible.”
Uranus is never visible in the same sense that Jupiter and Saturn are. ItÂ’s never easy to see with the eye alone. ItÂ’s certainly possible to see Uranus with the eye, but you need a very dark sky to do it. The planet Uranus reaches its opposition tonight. ItÂ’s up in the east-southeast after sunset, in front of the constellation Aquarius the Water Bearer. -
Friday, September 2, 2005
Looking West-Northwest One Hour After Sunset
A skywatcher writes, “I heard that one of the stars in the Big Dipper was a double star. Is this true?”
Actually, many stars in the sky that appear single to the eye are really multiple star systems. They consist of two, three,or more stars -- bound by gravity -- all orbiting each other in complex yet orderly ways. So every constellation has double stars.
We didnÂ’t check to see how many double stars there are in the Big DipperÂ’s constellation Ursa Major the Greater Bear, though, because we suspect the stars youÂ’re asking about arenÂ’t actually a true double star system.
How can this be? The most famous “double” in the Big Dipper is the second star from the end of the Big Dipper’s handle. If your sky is dark enough, and your eyesight is good, you’ll see that this star, Mizar, has a nearby companion, called Alcor. Can you see it on our chart? On our chart, Alcor is a tiny dot just above Mizar.
Astronomers still don't know if these two stars are a true double star system or not. They don't seem to be bound by gravity. The pair is often referred to a “naked-eye double star” -- appearing double from our earthly vantage point, but not really linked in any way.
Still, I’m sure it’s Mizar and Alcor you’re asking about, because these two stars are famous. Arabian stargazers called them the “horse and rider.” These stars are a good test of the night’s viewing conditions: if you can’t see Alcor, there might be thin clouds up there. Also, they’re a good test of your eyesight! -
Saturday, September 3, 2005
Looking Northeast in Late Evening
Here's a close-up look at the constellation Perseus the Hero. The brightest star in Perseus is Alpha Persei, or Mirfak. But the best-known star in this constellation is Beta Persei, or Algol -- whose proper name comes from the Arabic for "head of the ghoul," or "head of the demon."
Algol is known to vary in brightness in a way that's extremely regular. The cycle lasts exactly 2 days, 20 hours and 49 minutes. For a few hours during the cycle, Algol's brightness falls far below normal, then returns to normal. All the while, the star remains visible to the eye. Algol's brightness variation is not due to some special quality of a single star. Instead, this is a multiple star system, where one star regularly passes in front of another as seen from our earthly perspective. Thus Algol is what's called an "eclipsing variable star."
Thousands of these stars are known, but Algol is perhaps the most famous of this class because its periodic dip in brightness can be seen with the eye alone, and because the cycle is relatively short.
The ancient stargazers had no knowledge of multiple star systems, but it's thought they did notice this star's brightness change. It's thought that the brightness change is why, throughout parts of the ancient world, the star Algol was associated with demons or monsters. The Greeks and Romans identified the star with the Head of Medusa, a fearful monster with snakes in place of hair. The star has also been called The Ghoul Star. -
Tuesday September 6, 2005
Looking West-Southwest One Hour After Sunset
We have gotten some questions lately from eager skywatchers that go something like this: “What are those three planets in the west in evening?”
There are indeed three bright objects close together in the west-southwest shortly after sunset. Two of these objects are in fact planets -- one is Venus, easily distinguishable from the other two, as it outshines both them and all other objects in the sky (except for the moon of course.)
The other planet is giant Jupiter, the second brightest object of the three, and located to VenusÂ’ lower left.
The third object, located to the lower right of Venus might easily be mistaken for a planet given its brightness and its prominent location in the sky. However, this bright object is no planet -- it is the star Spica, the brightest star of the constellation Virgo the Maiden. Virgo is seen as a goddess of the harvest, and the name Spica means "ear of grain."
Notice the pink line across today's chart. This line represents the "ecliptic," or path of the sun, moon and planets. Spica's location near this line has always marked it as a special star, since ancient times.
Another star that happens to lie near the ecliptic is Antares, in the constellation Scorpius, located in the south-southwest after sunset.
Tonight you may catch a young waxing crescent moon below this three object grouping. Over the next several days, if you watch, you'll see the moon grow thicker and move progressively eastward along the ecliptic from one night to the next. By September 10, the moon will appear close to Antares on the sky's dome. -
Mid-September, 2005
Looking Southeast One Hour Before Sunrise
The most prominent constellation up before dawn right now is the famous constellation Orion the Hunter.
A skywatcher from Nashville wrote, "When will Orion return to the evening sky?"
Orion the Hunter is always behind the sun as seen from Earth in June. It comes back to the predawn sky every year in late July. By early-mid September, Orion is rising by about 3 a.m. and is well up in the southeast an hour before dawn, as shown on today's chart.
This chart also shows Orion's two Hunting Dogs, Canis Major the Greater Dog and Canis Minor the Lesser Dog, following behind it across the sky. Orion will soon be up by midnight, then 10 p.m. . . . and by December you'll find it rising in early evening.
There's nothing unusual about Orion's shift from the predawn to the evening sky. This constellation is simply following the westward shift of all the stars, caused by Earth's orbit around the sun. As we orbit the sun, our night sky points out on an ever-changing panorama of the Milky Way galaxy. Our orbit causes all the stars to rise approximately 4 minutes earlier each day. -
Sunday, September 11, 2005
Looking South-Southwest One Hour After Sunset
We often get this question about the moon: "Why do we say the moon is in 'first quarter phase' when it clearly looks like it is half-lit?"
If you started counting at new moon on September 3rd, the moon is now one quarter of the way around in its monthly orbit of Earth. And so we call this phase of the moon the "first quarter" phase. Tonight's first quarter moon looks half-illuminated, and some people will call it a "half moon."
But remember that, from Earth's surface, we can see only half of the moon's globe at any one time. Thus the part of the moon that looks half lighted to us tonight is really only a quarter of the whole round globe of the moon. Of course, half of the whole globe of the moon is always illuminated, just as Earth is always half illuminated, by the sun. But as the moon orbits Earth, we see various fractions of the moon's lighted half or various phases of the moon.
It's always fun to see the moon at first quarter. According to folklore, the time of a waxing moon is a good time to start something . . . to get married, for example, or start a new business. And there is some quality of the waxing moon that seems to say, "Be more." This particular first quarter moon has company. It's located near the famous hook in the constellation Scorpius the Scorpion. -
Tuesday, September 13, 2005
Looking South-Southwest One-Two Hours After Sunset
Today's chart faces southwest around 9 p.m. Tonight you can find the waxing gibbous moon up in the southern part of the sky.
If you go to a country location around that time some evening soon, and look towards that direction, sweeping your gaze southwest over the horizon, you'll be looking in the direction toward the center of our Milky Way galaxy. It's easy to pick out a couple of prominent constellations in this part of the sky.
One is the constellation Scorpius the Scorpion, with its bright reddish star Antares. Just east of Scorpius on the sky's dome -- and in the direction where the moon is tonight -- is the constellation Sagittarius the Archer It's Sagittarius that lies in the direction toward the center of the Milky Way.
Modern stargazers also speak of two other patterns superimposed upon these stars. One is the "Teapot" pattern in Sagittarius. Can you see it on our chart? The star Nunki is in the Teapot's handle, while Kaus Australis is part of the base of the Teapot.
After you've found the Teapot, focus on its handle and half of its lid. These stars make up the second pattern, called the "Milk Dipper" in Sagittarius. In a dark-enough sky, the Milk Dipper appears to be scooping up billowy clouds in the starlit band of the Milky Way, which is the edgewise view into our own galaxy, and which is shown in blue on today's chart.
As Earth moves around the sun, and our night sky points out in different directions, the center of the Milky Way becomes prominent in the evening in late summer and then begins to drift out of view again. Around now, you can still look toward the galaxy's center . . . in the direction of Sagittarius . . . in the evening. But soon Sagittarius and the multitude of brilliant, distant stars in its direction will set for another season. -
Wednesday, September 14, 2005
Looking South One-Two Hours After Sunset
If you contrast todayÂ’s chart to yesterdayÂ’s chart, youÂ’ll see that the moon has moved as it always does, eastward on our skyÂ’s dome from night to night.
This motion of the moon across our sky throughout each month is due to the moonÂ’s eastward motion in orbit around Earth. The moon takes about a month to orbit Earth, and thus the moon moves around our entire sky in that period of time.
WeÂ’ve marked the Teapot pattern again today, in the constellation Sagittarius. But the pattern we want you to notice tonight is below the Teapot on the skyÂ’s dome. This pattern appears in a dark country sky as an unfinished circle of stars. ItÂ’s really very graceful and lovely, if your sky is dark enough. People in southern states can see this constellation better than those up north . . . because the farther south you go on EarthÂ’s globe, the better you can see the southern part of the sky.
This semi-circle of stars has a name evocative of southern skies, which were first glimpsed by northern hemisphere dwellers who sailed into southern seas. This is one of the 88 official constellations, despite the fact that it doesnÂ’t contain even one bright star. ItÂ’s called Corona Australis, the Southern Crown. -
Thursday, September 15, 2005
Looking Southeast One-Two Hours After Sunset
In today's chart, we introduce the so-called "loneliest star." It's Fomalhaut in the constellation Piscis Austrinus, the Southern Fish.
Fomalhaut is just now coming back to a place convenient for evening viewing. In late September, it rises within an hour of sunset and afterwards arcs across the southern sky throughout the night. And this evening, Fomalhaut is the brightest star near the moon. Like all stars, this one will rise about four minutes earlier each day as Earth moves in its orbit around the sun.
Fomalhaut will arc across the south earlier and earlier each evening as autumn progresses toward winter. In other words, in another month, you'll see Fomalhaut higher in the southeast around this same time of night. A month after that, you'll see it in the south in early evening. Fomalhaut makes its trek across the southern sky while autumn leaves are falling for inhabitants of the Northern Hemisphere.
Learn to recognize it now, and you can count on this star to shine in the south each autumn for the rest of your life . . . as long as you stay in this hemisphere! Fomalhaut is easy to recognize, even without the moon nearby, because it is the only bright star in its region of the sky. That's why it's sometimes called "the loneliest star." -
Friday, September 16, 2005
Looking East-Southeast One Hour After Sunset
If you have never seen the constellation Aquarius the Water-Bearer -- IÂ’m not surprised.
Aquarius is a constellation of the Zodiac, meaning that it follows the sunÂ’s path across the sky (marked by the pink line on todayÂ’s chart). But it is faint, even when seen in dark skies. The easiest way to find Aquarius in the sky, is to first locate something brighter that is near it.
Tonight, a nearly full moon will be in AquariusÂ’s company until it sets. This may not be the time for an attempted first viewing -- the almost-full moon (the famous Harvest moon doesnÂ’t officially reach its full status until tomorrow) may drown out a good view of Aquarius.
However, if you have binoculars, you may try to pick out its stars against the moonlight. Just be aware that the brightest stars in this constellation are still rather faint.
Also near the moon this morning is the planet Uranus, located to the upper right of the moon, and probably even harder to pick out than Aquarius.
We recently had a question about viewing the planet Uranus with unaided eyes. ItÂ’s certainly possible to see Uranus with your eyes alone, but you need a very dark sky to do it. Your best chance to view the planet Uranus with the unaided eye is going on right now. Uranus reached its opposition on September 1st, and is out in the sky all night long now. Your best bet is to wait a couple of days until the moon has moved on from this area of the sky, and then see if you can get a gander at this faraway planet. -
Saturday, September 17, 2005
Looking East-Southeast After Sunset
The full moon that rises around the time of sunset this evening is the legendary Harvest Moon. It has that name because it's the closest full moon to the September equinox.
Some say the Harvest Moon appears bigger, brighter and yellower than other full moons. But all full moons look big, bright and yellowish when you see them near the horizon. What makes the Harvest Moon special is the lazy slant of the ecliptic -- shown on our chart as a pink line -- with respect to the horizon in the evening at this time of year.
As the moon moves in orbit around Earth, it moves eastward approximately along the ecliptic. Most of the time, the moon's eastward motion causes it to rise about 50 minutes later each day.
At this time of year, however -- around the time of full moon -- the moon rises only about 30 minutes later each day. That's why, around the time of full moon during the autumn months, the moon rises close to the time of sunset several evenings in a row.
So you have several chances around now to see a big yellow moon hanging low in the sky just after the sun goes down. Before the era of tractor lights, farmers bringing in their crops could work uninterrupted by the light of this full autumn moon. -
Sunday, September 18, 2005
Looking East-Southeast in Mid-Evening
The constellation Pegasus represents a Flying Horse. Here's where you can look to see the constellation Pegasus tonight. If you look due east around 10 P.M., you may catch glimpse of a large square pattern of stars. This pattern lies at the center of the constellation Pegasus.
This square star pattern, by the way, has its own name. It's called the Great Square of Pegasus, and it's easy to pick out. The Great Square marks the body of the Flying Horse. The star Enif marks the tip of the Horse's nose. The brightest star in Pegasus is Markab, whose total luminosity is 205 times that of our own sun. The star Alpheratz -- although located in the Great Square -- is actually part of a neighboring constellation Andromeda.
In the mythology of the sky, Pegasus was born from the blood of the serpent-haired Medusa. After Perseus, a hero of ancient mythology, killed Medusa and cut off her head, some of her blood dripped into the sea. From it, the sea god Poseidon fashioned the Flying Horse. He gave the Horse to Perseus -- who rode the Horse while having his great adventures!
Tonight, you'll find the slightly waned Harvest Moon accompanying Pegasus in the southeastern vicinity of the sky at that time. -
Monday, September 19, 2005
A skywatcher in southern Arizona wrote, "I've recently used Cassiopeia as a pointer to find another very prominent galaxy, the Andromeda Galaxy . . . I used the larger V portion of Cass as an arrowhead, and traced a line with binoculars southward until I located the fuzzy cotton ball in the sky . . . I've read there are an estimated 500 billion stars in that galaxy, and was awestruck with the thought of the possible worlds orbiting those very distant stars. . . I'll bet you have an easier way to find it than I did!"
What a wonderful experience to share! Indeed, in a very dark sky, it's possible to locate the Andromeda Galaxy in the way described above, by starting at the star Schedar in the W-shaped constellation Cassiopeia and "eye-balling" your way to the galaxy. In a very dark sky, the galaxy is visible to the eye.
Most amateur astronomers, however -- when learning to locate the Andromeda galaxy -- learn by starting with the star Alpheratz, which marks a corner of the Great Square in the constellation Pegasus, found in the east in mid-evening.
Alpheratz is actually Alpha Andromedae, the brightest star in the constellation of Andromeda, which you can see on today's chart extending from the Great Square in two graceful streams of stars. Notice that, from Alpheratz, as you go up along these streams, you come to a pair of stars, unmarked on our chart today. Then you come to a SECOND pair of stars -- Mirach, also known as Beta Andromedae, and its neighboring star Mu Andromedae. Notice that Mirach and Mu Andromdae also point to the Andromeda galaxy!
You might notice that the moon seems to rise at almost the same time as it did yesterday evening. On average, the full moon rises approximately 50 minutes later each night after sunset. Around this time of year, the narrow angle of the ecliptic (the pink line on today's chart) to the horizon in the evening causes a shorter time between successive moonrises. This phenomenon is characteristic of the recent full moon, which occured on September 17th, known as the Harvest Moon. -
Tuesday, September 20, 2005
Looking West-Northwest One Hour After Sunset
Many people have asked about the reddish star in the west-northwest after sunset. Every year at this time, we get questions about three different stars that are flashing different colors.
One is Capella in the constellation Auriga the Charioteer, which is now in the northeast in mid-evening. One is Sirius in the constellation Canis Major the Greater Dog, which now is climbing in the southeast before dawn. And the third is the one in the west to northwest after sunset. This star is Arcturus in the constellation Bootes the Herdsman. ItÂ’s flashing colors for the same reason Sirius and Capella are . . . because all three of these stars are bright and, at this time of year, noticeable low in the sky.
When you see an object low in the sky, youÂ’re seeing it through a greater thickness of atmosphere than when itÂ’s overhead. The atmosphere refracts or splits the starsÂ’ light to cause the colorful flashing you observed.
By the way, Arcturus is located along a line extending off the handle of the Big Dipper. ThatÂ’s one way you can be sure the star you think is Arcturus actually is. Just look for the Big Dipper in the constellation Ursa Major the Greater Bear. Draw an imaginery line out from the curve of the DipperÂ’s handle, and youÂ’ll come to the star Arcturus. -
Thursday, September 22, 2005
Looking West-Southwest One -Two Hours Before Dawn
One of you wrote, "How can I find out where the moon will rise and set each night? Not just the time, but the location . . . "
If you begin watching the moon, you can get a feel for the cycle of its rising and setting times. Or you can use the Navy's Complete Moon and Sun Data website to calculate your daily local moon rise and set times.
Just be aware that the moon doesn't always rise at night. On last Saturday's full moon, for example, it rose in late afternoon and began shining like a bright beacon in the southeastern sky, as soon as the sun set. The moon rises in daylight half the time, and at night the other half. It rises, on average, about 50 minutes later each day. Thus it really is possible to get a sense of what time the moon will rise, if you watch (or check a chart) and just try to be aware.
On the other hand, I can't give you much hope for understanding the location of the moonrise on the horizon, because it varies seasonally as well as throughout the month. The best I can do is say that the moon -- like the sun, or like planets or stars -- always rises more or less in the east. That's because Earth spins toward the east, and it's Earth's spin that brings the moon into view each day.
Finally, for those of you who are interested, we have an article explaining the moon's phases on this site. Tonight's moon rises in mid-evening, and you may notice that it is accompanied by quite a conspicuous object. This dazzling yellow-orange object is no star -- it's our fiery neighbor planet Mars. Mars will continue to keep the moon company throughout the night until they both set in late morning on the 22nd. -
Thursday, September 22, 2005
Looking East at Sunrise
Today the sun crosses the celestial equator, moving from north to south. This is the September equinox, which many call the “autumnal” equinox . . . but which also marks the beginning of spring on the southern half of Earth’s globe.
We get a lot of questions each year about the easiest way to find north,east ,south, and west in the sky. At this and every equinox, the sun rises due east and sets due west. So try going outdoors at sunrise or sunset today or tomorrow, preferably in a place where you can see the horizons. Simply make a 90 degree turn -- with respect to the sunrise or sunset -- to find the direction south. If you start out facing a sunRISE, turn 90 degrees to the RIGHT to find due south. If you're watching a sunSET, turn 90 degrees to the LEFT. Once you've found south, you know that north is directly behind you.
You can see the sun rising due east on today’s sky chart. The pink line on our chart marks the “ecliptic,” or path of the sun, moon and planets, and you can see that it makes a very steep angle to the horizon on these autumn mornings in the northern hemisphere. Today’s equinox happens at precisely 22:23 Universal time. -
Friday, September 23, 2005
Looking West-Southwest After Sunset
As recently as early this month, we were hearing from a lot of people who were glimpsing Jupiter making lovely patterns with Venus, the star Spica, and the moon in the west after sunset.
Now this giant planet is making its way towards the horizon in late afternoon, becoming lost in the sunset glare. It’s blocked from view by your horizon, by the time the sky gets dark. From a three-dimensional perspective, Jupiter is now traveling on the far side of the sun from Earth. Its “conjunction” with the sun will come on October 22. Afterwards, it’ll come back to the eastern sky before dawn.
When can you expect to see Jupiter next? By late November, itÂ’ll be only 10 degrees above the east-southeastern horizon before dawn at the beginning of morning twilight. Jupiter is so bright that you should be able to glimpse it then.