In the Sky Tonight

last SG · 2005-08-23T14:26:28+00:00

Spotting the Summer Triangle Wednesday, May 17, 2006 Looking East-Northeast in Late Evening In the east-northeast in late evening, you'll find a famous...

poon cho tang SG

Moon near Mars next couple of nights

Saturday, March 4, 2006

Looking West-Southwest in Early Evening

Today's chart is a close up view of the west-southwestern sky, see yesterday's chart to orient yourself to the horizon. The waxing crescent moon has now moved near the red planet Mars, and will be there tonight and tomorrow. Today it is closest to 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. 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.

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Two red "stars" near moon

Sunday, March 5, 2006

Looking West-Southwest in Early Evening

If you look outside in mid-evening, you'll find the waxing crescent moon in the west-southwestern sky. Today's chart is a close up view of this area -- for a chart that shows a reference to the horizon, look back at our chart for March 3rd. Tonight the moon appears just to the lower right of the red planet Mars. Mars -- which was a brilliant beacon of light in our sky about 5 months ago -- is now barely able to keep its luster brilliant enough to distinguish it from its nearby red star rival, Aldebaran.

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Find the anticenter of the galaxy

Monday, March 6, 2006

Looking West-Southwest in Early Evening

Here is an important star for gaining astronomical perspective. To orient this chart, look high in the west-southwest in mid-evening to find the star above the moon. El Nath is a star in the constellation Taurus the Bull. In the fancy of the ancient stargazers, it was the star that marked the tip of one horn of the Bull. To modern astronomers, however, it is more relevant that El Nath lies nearly in the direction of the anti-center of our Milky Way galaxy. The anti-center is the point on the skys dome opposite the center of the galaxy. And El Nath is three degrees west of this point. You might find this confusing -- because there are two systems of perspective at work here. One is the perspective that our galaxy, the Milky Way, is a real three-dimensional realm always surrounding us in space. Our sun and solar system are thought to be located about two-thirds of the way from the center of the galaxy, and, in winter, our night sky faces opposite the center. The other perspective at work here is that there is a sphere of stars surrounding Earth, on which distances -- like three degrees west of this point -- can be measured. This celestial sphere is imaginary, of course, but it is convenient! Thus El Nath lies three degrees west of the anti-center of the galaxy -- that is, three degrees west of the point on our skys dome opposite the galaxys center.

poon cho tang SG

Find Jupiter, Scorpion tomorrow morning

Wednesday, March 8, 2006

Looking South Before Sunrise

Jupiter is bright and high in the south about one hour before dawn. Dont confuse Jupiter with the really bright star in the east at this time, thats the planet Venus. Besides the difference in brightness, you know you have Jupiter in your sights if you can learn to identify the constellation Scorpius the Scorpion, which currently rests to the left of Jupiter. Luckily, Scorpius is a constellation that actually looks like its name! The top stars of Scorpius -- Graffias, , and Pi Scorpii -- are collectively known as the Crown of the Scorpion. The bottom part of Scorpius looks like a giant fishhook. Its brightest star is Antares, known as the Heart of the Scorpion.

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Find Twins constellation with moon tonight

Wednesday, March 8, 2006

Looking High in the West in Late Evening

Tonight in late evening, the waxing gibbous moon can be found high in the west. The bright pair of stars near it are the twin luminaries of the constellation Gemini, Castor and Pollux. 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. The golden planet Saturn (along with the constellation Cancer) can be find ito the upper left of the moon, and along with the star Procyon (located to the lower left) and the Twin stars of Gemini form a triangle surrounding the moon.

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Astrology vs. astronomy

Thursday, March 9, 2006

Looking North-Northeast at Nightfall

Can you explain the discrepancy between astrological dates and actual astronomical positions of the sun in the zodiac?

The difference is due to Earth's motion of precession, which causes Earth's northern axis to point out in different directions over time. Basically, precession causes the north celestial pole to trace out a circle among the northern stars over 26,000 years. Right now, the northern axis points more or less to Polaris, but 12,000 years ago it pointed to Vega, a bright star which is below the horizon at the time of this charts setting. Thus our orientation with respect to the sky shifts continually, and that's why astronomy and astrology have parted company.

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Moon, Saturn and company

Friday, March 10, 2006

Looking South-Southwest in Early Evening

Here is a wide view of the south-southwestern sky around early evening, where you will find the waxing gibbous moon accompanied closely by the golden ringed planet Saturn. Also of note in this area of the sky is the conspicuous Hunter constellation Orion, particularly easy to identify due to its three "Belt" stars. The particularly bright star in the south is the dogstar Sirius -- the brightest star in our sky. The two bright red objects in the southwest are the planet Mars and the star Aldebaran of the constellation Taurus. Since they are now of similar magnitude, today's chart may help you determine which is which through their positioning. The star couple near to the right of Saturn and the moon are the so-called "twin" luminaries of the constellation Gemini -- Castor and Pollux.

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Identify a double star in Leo

Sunday, March 12, 2006

Looking East After Sunset

As soon as the sky darkens, look eastward for the waxing gibbous moon in the midst of the constellation Leo the Lion. Leo lies more or less on the sun's path as seen from Earth -- marked on our chart with a pink line. Because Leo lies along this path, the sun, moon and planets all sometimes move in front of it. It's also why some of you scan the horoscope in your daily newspaper for Leo . . . Leo's location along the sun's path is what makes it a "zodiacal" constellation, or constellation of the Zodiac. Notice the six stars in Leo in the shape of a "backwards question mark." This pattern represents the head and shoulders of the Lion, and has its own name, the Sickle. Regulus is Leo's brightest star, as well as the brightest star in The Sickle, but the star Algeiba is also a favorite. It's really two stars, difficult but possible to "split" with a small telescope. The double system we know as Algeiba is located about 100 light-years away. The two stars in the system are separated by about 150 times Earth's distance from our sun, and they're believed to take 600 years to complete a single orbit around each other. In the past century, skywatchers gazing outward from Earth have seen these two stars draw slowly but inexorably farther apart, as they move in their vast mutual orbit. It's believed their maximum separation will come about another century from now.

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Hunter and Scorpion legend

Monday, March 13, 2006
Looking South in Early Evening

Tuesday, March 14, 2006
Looking South-Southwest Shortly Before Dawn

Many of our charts for the past month have depicted the famous constellation Orion the Hunter. To find Orion, which is up in the south in early evening, use our left chart to orient yourself. But there is one constellation you wont find in the evening sky now, even though its associated with Orion in the lore of the sky. Its the constellation Scorpius the Scorpion, shown on todays right chart where youll find it at this time of year . . . accompanying bright Jupiter, rising in the southeast shortly before dawn. You might spot Antares, the brightest star in this constellation, which represents the Scorpions ruby heart. Next summer, when Orion is up before dawn, Scorpius will be up in the evening. Legend has it that Orion the Hunter was very vain. He boasted that no animal on Earth could kill him. But the Scorpion did sting Orion, and the Hunter died of its poison. Now, according to this ancient myth, the bitter hatred between these two constellations is so great that they can never been seen in the sky simultaneously. We today have a different interpretation of the fact that Orion and Scorpion are never in the sky together. Scorpius is located in the direction toward the center of our Milky Way galaxy. Orion is located in the opposite direction, toward our galaxys nearest outer edge.

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Stars near the eclipsed moon

Tuesday, March 14, 2006

Looking East at Moonrise

When you see the full moon rise this evening, it'll be in the midst of a brush with Earth's shadow. This is a penumbral eclipse, which happens when Earth's shadow sweeps across the moon's face. In this sort of eclipse, however, it's not the dark inner part of Earth's shadow, called the "umbra," that encounters the moon. Instead, the lighter, outer part of Earth's shadow brushes the moon's face tonight. This lunar eclipse -- visible but in progress at moonrise for most of the U.S. -- will not be seen at all by the westernmost parts of North America, such as British Colombia.

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Ring around the moon

Wednesday, March 15, 2006

Looking East-Southeast in Mid-Evening

Full moon (and a penumbral eclipse) was last night. And so the moon is still very bright tonight, although it won't look quite as full. What's more, the moon won't rise so close to the time of sunset tonight as it did last night. On average, the moon rises 50 minutes later each evening. But it rises one hour and 20 minutes later tonight, in contrast to last night, as seen from 35 degrees N. latitude. This change in the time of moonrise on subsequent nights is seasonal. It relates to the angle of the ecliptic, or path of the sun, moon and planets, with respect to the eastern horizon. We get many questions about rings around the moon and rings around the sun. They're really pretty common, but they're so striking and eerie-looking that people are always surprised to see them. In fact, these rings are caused by moonlight (or sunlight) shining through ice crystals in the upper atmosphere. They are especially easy to see around a moon that's full, or nearly full.

poon cho tang SG

Are stars in constellations connected?

Looking South in Early Evening
Thursday, March 16, 2006

Looking South-Southwest Before Dawn
Friday, March 17, 2006

The constellation Orion the Herdsman can be found in the south at nightfall. A reader wrote In the constellation Orion, if you were to draw a line from Earth to each star would their distances be the same? The stars in Orion aren't the same distance from Earth. Most stars in constellations aren't physically bound to each other in any way. A notable exception is in the case of the stars of the constellation Scorpius the Scorpion. The Scorpions stars lie at very different distances from Earth. In the case of Orion, the brightest stars in the constellation lie at similar distances, hundreds of light-years away. Rigel is 773 light-years away, Betelgeuse 522 light-years, Saiph 815 light-years and Bellatrix 243 light-years. These are all just estimates, of course. That's in contrast to the nearby bright star Sirius, which is only 9 light-years away. It's no coincidence that these stars in Orion lie at such similar distances. When we look toward Orion, we're looking toward the outer edge of the galaxy . . . but into the very arm of the galaxy in which our sun resides (or near which our sun resides . . . astronomers aren't sure). So these bright stars in Orion just happen to be giant stars in that nearby spiral arm of our Milky Way galaxy.

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Find two prominent constellations

Thursday, March 23, 2006

Looking South-Southeast Shortly Before Dawn

Thursday morning before dawn, the moon is located in the constellation Sagittarius the Archer, and this coupling is located just to the left of the conspicuous constellation Scorpius the Scorpion. If you happen to be standing under a dark country sky, you might be able to glimpse the starlit trail of the Milky Way in this direction in space. Just wait a few days until the moon disappears from this part of the sky. Then, in a dark sky, you'll easily see the Milky Way in the southeast before dawn, extending from there across the entire sky. Just know that when you look at this hazy "pathway" of starlight across our sky, you're gazing edgewise into the flat disk of our own galaxy. The constellation Sagittarius marks the direction to the galaxy's center.

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Locate the Big and Little Dippers

Thursday March 23, 2006

Looking North-Northeast After Sunset

People often ask, How can I locate both the Big and Little Dippers? I am seeing one of them in the sky . . . but cannot tell which one and where the other one is. If youre seeing only one dipper, and its a large sky figure, its probably Ursa Major. If youre seeing a dipper pattern, and its very very tiny, then you might be looking at the Pleiades star cluster . . .for more about this cluster, see our chart for March 4th. The actual Big Dipper is part of the constellation Ursa Major, the Greater Bear. Here it is, on todays chart, shown ascending in the northeast in the early evening at this time of year. Ursa Minor, the Lessor Bear, which contains the Little Dipper asterism, is much harder to see. Its stars are fainter, and the dipper shape isnt so obvious. But its easy to spot, once you realize that the North Star is the last star in its handle. How do you find the North Star? As todays chart shows, the two outermost stars in the Big Dipper always point to the North Star. Thats why these two stars, Dubhe and Merak, are known as The Pointers.

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Venus reaches greatest elongation west

Saturday, March 25, 2006

Looking Southeast Shortly Before Dawn

Here is a view of the southeastern sky right before sunrise. You can see the planet Venus shining bright. You might notice the very slim waning crescent moon to the left of our sister planet, but youll probably not notice the planet Mercury located to the right, as it will be hard to detect from the glare of morning twilight. Today Venus reaches whats called its greatest western elongation. That means the planet is farthest in its angle from the sun for its predawn apparition. In order to try to get a glimpse of elusive Mercury, you will definitely need a pair of binoculars and an unobstructed eastern view of the horizon -- though struggling against the twilight of dawn will make viewing difficult.

poon cho tang SG

Crescent moon, crescent planet

Monday, March 27, 2006

Looking East-Southeast Shortly Before Dawn

Look southeastward, not long before sunrise, to find the waning crescent moon. There are two planets near the moon tomorrow and the next morning: Mercury and Venus. Venus is the much brighter planet. A reader wrote, I saw what I think was Mars (though it could have been Venus) quickly approaching the horizon. The weird thing was that the top half of the planet was in shadow like a half-full moon! What gives? Were assuming you were looking through a telescope. Youd need a telescope to see the phase of a planet. Only the inner planets, Venus and Mercury, show phases. Thats because, in order to show a phase, a planet has to be able to come nearly between us and the sun . . . which the outer planets (Mars, Jupiter, Saturn and so on) cant do. So the planet you saw in a half-moon phase wasnt Mars. It must have been Venus, now the brightest object in the east before sunrise. Tomorrow morning, with the eye alone, you can see a slim fraction of the moons day side (a crescent moon) . . . and probably a large portion of its night side as well, glowing dimly with sunlight bouncing off Earths day side. There is a shadow on the moon, but its the moons own shadow. Likewise, the shadow of Venus, cast back away from the sun, creates night on that neighboring world . . . just as night on Earth comes each evening when our world spins you into Earths shadow. Theres only a fraction of the venusian day side facing our way tonight. And thats why we see a crescent Venus.

poon cho tang SG

Start tracking two evening planets

Monday, March 27, 2006

Looking from Southwest to Northwest in Mid-Evening

Today's chart shows a sweeping view of the sky from the southwest to the northwest direction at about 9:30 PM central time. Among the many bright and recognizable objects in this area -- the brightest star Sirius and the constellation Orion the Hunter being the most conspicuous in the southwest -- we would like to point out two objects in particular. High in the west-southwestern sky is the golden planet Saturn, most easily identified because of its close proximity to the Gemini twin stars Castor and Pollux. Lower in the western horizon, you may catch sight of two reddish colored stars. One of them is the star Aldebaran and the other is the planet Mars (the object we'd like you to notice.) How to tell them apart? For one, Mars is the red object higher in the horizon, but a more sure way is to see if you can see a distinctive "V" shaped pattern coming from one of the red objects. Aldebaran is the brightest star of this pattern. Today would be a great day as any to start noting the movements of Saturn and Mars in the sky. By mid-June, 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.

poon cho tang SG

Find the Hunting Dogs

Tuesday, March 28, 2006

Looking East-Northeast In Mid-Evening

We've been talking a bit this month about locating stars using the Big Dipper as a guide. The Big Dipper is part of the constellation Ursa Major, the Greater Bear. And, if you can find the Big Dipper -- now in the northeastern sky at mid-evening -- you can also find two Hunting Dogs seen by the ancient stargazers to be nipping at the Bear's heels. The Hunting Dogs are a separate constellation -- tiny Canes Venatici. You'll need a dark sky to see these two little stars snuggled in the arc of the Big Dipper. Originally, they were called Asterion and Chara. But the eastern star is now called Cor Caroli, or Heart of Charles, named for the patron king of the Polish astronomer Johannes Hevelius, who devised this constellation in 1690. The most famous object in this region of the sky is M51, the Whirlpool Galaxy. It's beautiful when seen through telescopes -- and dramatic in photographs. But this galaxy is difficult or impossible to glimpse with binoculars. But there's another faint object at the extreme edge of Canes Venatici that your binoculars should pick up, assuming you're looking in a dark sky, with no moon. This object is M3, a globular star cluster located some 48,000 light-years away. Binoculars see it as a dim blur of light, best seen with averted vision. Notice that it lies almost midway between the bright star Arcturus and Cor Coroli.

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Total eclipse of the sun

Conceptual Space View of Earth, Moon, and Sun (Not to Scale)

All day on Wednesday, for all of us on Earth, the moon is hidden in the sun's glare. Wednesday's moon crosses the sky with the sun during the day. The moon and sun set at nearly the same time Wednesday evening, so you won't see the moon in the night sky. This monthly event is called "new moon," when the moon is more or less between us and the sun for this monthly orbit. The moon usually passes above or below the sun in our sky at new moon. If the new moon passes DIRECTLY in front of the sun (as it does today), the moon's shadow falls on Earth. Our chart today shows a crude outer space view of this. Please note that it is not drawn to scale. Those standing in the shadow's path see a solar eclipse. There are from four to seven eclipses each year -- some solar, some lunar, some total, some partial. Today brings our first solar eclipse of 2006. It's a total eclipse, visible along a narrow strip that traverses half the globe. This strip starts in Brazil and travels through north Africa and ends in central Asia.

poon cho tang SG

Find Capella via the Hunter

Thursday, March 30, 2006

Looking West-Southwest in Early Evening

If you look towards the west in early evening, you can find the familiar pattern of the constellation Orion the Hunter, lying more or less on the sun's path as seen from Earth, or the ecliptic path. That path is marked on our chart with a pink line. You can easily recognize Orion by his famous belt, which is comprised of the three bright stars Alnitak, Alnilam and Mintaka, which form a straight line. If you look to the upper right of Orion, you will see a bright yellow object shining high in the sky. That bright star is Capella, the crowned jewel of the constellation Auriga the Charioteer. Capella is actually a cluster of celestial bodies composed of about at least nine stars. This cluster itself forms a binary star system, which is really two stars (or two groups of stars in this case) that are in rotation with each other around a common center of mass. All these groups and masses make up the Capella that we see when we look in the night's sky.

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