Archive for the 'Astronomy' Category

Go Stargazing! September Edition

Published
by
James
on September 2, 2010
in Astronomy and Science
. 0 Comments

Venus and Mars have left Saturn behind in the night sky (check out my earlier blog on the position of the planets). You can spot the star Spica in between Mars and Venus during this time of year. (Spica is similar to Mars in brightness and closer to Venus than to Mars). 

 Cloud structure in The Venusian atmosphere,
revealed by ultraviolet observations

September is the last full month to observe Venus at dusk. That’s because Venus has by now come around to Earth’s side of the sun on its faster, inner orbit.  Thus, Venus now begins to overtake the Earth, passing between the Earth and sun on October 29.  We’ll therefore see Venus shift farther to the left of Mars and then drop down below it.  In October, Venus exits the evening sky quite quickly as it shifts back towards the sun.  September and October 2010 is an excellent period for observing Venus’ crescent phase in telescopes.  Anytime Venus is on our side of the sun, more of its night side faces us, resulting in a crescent like appearance when magnified.

Saturn is far to the lower right of Venus and Mars as you face west at dusk.  You’ll need a horizon clear of tall buildings and trees to see it before it sets.  You’ll also need to look early in the month, as Saturn is practically behind the sun by month’s end.  

Jupiter dominates this month’s skies.  On Tuesday morning, September 21, Earth aligns with the sun and Jupiter, bringing Jupiter to opposition (because the sun and Jupiter are then on opposite sides of the Earth).  On the night of September 20-21 we see Jupiter rise at sundown and set at sunup—Jupiter is up literally all night long.  During the whole month, though, Jupiter is visible virtually the whole night.  It outshines all stars in the sky, so it’s easy to find.  Face east in late evening or south southwest at dawn to see it.  The planet Uranus is less than one degree above Jupiter this month; the two planets are closest on September 18.

The Big Dipper is setting in the northwest at dusk; you now need a horizon clear of trees and tall buildings to get a good look at it. You can extend the curve of its handle to ‘arc to Arcturus’, which is in the west at dusk tonight.  Arcturus, by the way, is the fourth brightest star we ever see at night, but the brightest one Americans ever see on a September evening.

As the Dipper gets lower, look for five stars in the shape of an ‘M’ directly across the North Star from the Big Dipper’s handle.  This is Cassiopeia, the Queen—the ‘M’ is the outline of her throne.  Her stars are about as bright as the North Star and the stars of the Big Dipper, so she’s not too hard to find. 

星空下的汗腾格里峰 / Mt. Khan Tengri under Galaxy
Creative Commons License photo credit: livepine

High overhead, look for the enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair.   This triangle was up all night long from June to early August, hence its name.  Scorpius, the Scorpion, is in the southwest at dusk.  Sagittarius, the Archer, known for its ‘teapot’ asterism, is to its left.  Between these two star patterns is the center of our Milky Way—the brightest part of that band as wee see it.  On a cloudless night far from the big city, see if you notice the Milky Way glow near the ‘teapot’ of Sagittarius. 

Look for the Great Square of Pegasus rising in the east.  The vast stretch of sky under Pegasus is largely devoid of bright stars—ancients called this the ‘Celestial Sea”. 

Moon Phases in September 2010:

Last Quarter                  September 1, 12:22 am, September 30, 10:52 pm

New Moon                       September 8, 5:29 am

1st Quarter                     September 15, 12:49 am 

Full Moon                        September 23, 4:18 am

At 10:13 pm on Wednesday, September 22, the sun is directly overhead at the equator.  As a result, everyone on earth has the same amount of daylight and the same amount of night.  That’s why it is called the equinox (‘equal night’ in Latin).  In the Northern Hemisphere, we’ve seen the days get a little shorter and the midday Sun a little lower each day since June 21.  For us, the season changes from summer to fall at the equinox.  In the Southern Hemisphere, people have seen the days lengthen and the midday Sun get a little higher each day since June.  For them, the season changes from winter to spring.

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Spot the Planet Uranus with the Naked Eye

Published
by
James
on August 25, 2010
in Astronomy
. 0 Comments

The “Great Planet Race” in the western evening sky this summer is beginning to wrap up; Venus has caught up with Mars as they both leave Saturn behind. As these planets set in the west, though, another rises in the east at about 9:30, and will have cleared most buildings and trees by 10 p.m. And this one is involved in a conjunction of its own.

This is none other than Jupiter, king of the planets. Once Jupiter rises, it is easy to find because it outshines everything in the sky except the sun, the moon, and Venus.  Just look east for the brightest thing in the night sky.  Last I checked, Jupiter is still missing one of its belts.  For the rest of this year, Jupiter remains well placed for observing in convenient evening hours.  If you have a telescope, watch for yourself and see if the belt returns!

Although Jupiter seems to be by itself among the much, much dimmer stars of Pisces, it in fact has a close companion that few of us ever get to see without a telescope, the planet Uranus. We typically identify Mercury, Venus, Mars, Jupiter, and Saturn as the five naked eye planets, and for practical purposes, that’s true.  However, Uranus is actually visible to the unaided eye under perfect conditions.  In the time before man made light dimmed the skies, many people could see Uranus.  However, they were unable to recognize it as a planet because it is dim and changes position very slowly. (It takes 84 years for Uranus to reappear near the same stars).  Thus Uranus, although plainly visible, went undiscovered for centuries.  For example, in 1690, John Flamsteed was cataloguing stars and constellations, numbering stars in each constellation from west to east.  However, the ‘star’ he catalogued as ’34 Tauri’ (#34 in Taurus) was in fact the planet Uranus. 

 Replica of Herschel’s telescope

In March 1781, William Herschel became the first to identify Uranus as a planet when he observed it in his telescope.  As Uranus is about twice as far from the sun as Saturn, Herschel’s discovery doubled the size of the known solar system.  Herschel wanted to call the new planet ‘George’ (actually Georgium Sidus in Latin) after his patron, King George III.  German astronomer Johann Elert Bode, who had calculated an orbit for the new planet, suggested calling it ‘Uranus’ because in Graeco-Roman myth, Saturn had been the father of Jupiter and Uranus the father of Saturn. 

Here are charts showing the relative positions of Jupiter and Uranus from now into the new year.  The event depicted is a triple conjunction, in which two outer planets align on three separate occasions only a few months apart.  This occurs when distant planets align while Earth is on the same side of the sun as they are.  As Earth passes the slower outer planets, we see them slow down, stop, and reverse direction for while.  We see the planets resume direct motion once Earth has pulled far enough ahead on its much faster inner orbit.  As a result, we see three conjunctions instead of just one.  The three closest alignments of Jupiter and Uranus occur on June 8, 2010, September 18, 2010, and January 3, 2011.  At all three, Jupiter is less than one degree (about the width of an adult’s pinkie held at arm’s length) under Uranus.  The conjunction of June 8 occurred in the morning sky, but the two yet to come will be visible in convenient evening hours.  On the night of September 20-21, Earth is directly in line with the pair, causing them to rise at dusk at set at dawn–Jupiter and Uranus will be up all night long.  By winter, Jupiter and Uranus will be high in the south southwest at nightfall. 

Late 2010 is a good time to get a glimpse of a world we don’t usually notice in the sky.  A small telescope or even binoculars will reveal Uranus.  And if you find yourself away from the city on a moonless night, see if you can pick out which of the dim points of light just above Jupiter is a little more than meets the eye. 

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Go Stargazing! August Edition

Published
by
James
on August 2, 2010
in Astronomy
. 1 Comment

This month the great planet race continues, as Venus, Mars and Saturn form a triangle in the west.  Watch the triangle change shape each night as Venus overtakes Saturn and then Mars!

Venus is by far the brightest of the three planets.  Face west at dusk and look for a point of light that outshines everything in the night sky.

Saturn and Mars are to the upper left of Venus as August opens.  Mars is below Saturn and a bit to its left.  Although these two planets of similar brightness are much dimmer than Venus, they outshine all the other stars near them.

Observe all three carefully throughout August and watch as their configuration changes.  Mars aligned with Saturn last Saturday (July 31) and now begins to move farther to Saturn’s left.  Venus, moving faster than the other two, continues to approach from the right; it will pass Saturn on August 8.  Venus then continues to gain on Mars as they both move away from Saturn.  Venus finally overtakes Mars on August 19-20.  On the night of August 31, Venus and Mars are to either side of the star Spica in Virgo.

Jupiter is now a late evening object, rising by 11 p.m now and by 8:45 p.m. at month’s end.  It outshines all stars in the sky, so it’s easy to find.  Face east in late evening or south southwest at dawn to see it.

The Big Dipper is in the northwest at dusk. You can extend the curve of its handle to ‘arc to Arcturus’ and then ‘speed on to Spica’.  These stars are in the west at dusk tonight.  Arcturus, by the way, is the fourth brightest star we ever see at night, but the brightest one Americans ever see on an August evening.  Spica is in Virgo, the constellation where this month’s ‘planet race’ occurs.

In the east, look for the enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair.   This triangle is up all night long from June to early August, hence its name.  Scorpius, the Scorpion, is in the south at dusk.  Sagittarius, the Archer, known for its ‘teapot’ asterism, is to its left.  Between these two star patterns is the center of our Milky Way—the brightest part of that band as wee see it.  On a cloudless night far from the big city, see if you notice the Milky Way glow near the ‘teapot’ of Sagittarius.  In late evening, look for the Great Square of Pegasus rising in the east.

Moon Phases in August 2010:

Last Quarter                        August 3, 12:00 a.m.

New Moon                              August 9, 10:08 p.m.

1st Quarter                           August 16, 1:14 p.m.

Full Moon                              August 24, 12:05 p.m.

Perseid Meteor 8/12/08
Creative Commons License photo credit: aresauburn™

On Friday morning, August 13, the Earth passes through a stream of debris left long ago by Comet Swift-Tuttle.  This produces the Perseid Meteor Shower, one of the best meteor showers each year.   The Perseids occur every year at about this time, producing on average about one meteor per minute.  Keep in mind that even a short period such as a minute can seem longer if you are waiting for something to happen.  Since Earth is running into the meteors, not the other way around, the leading edge of the Earth encounters the shower.  This is the side going from night into day.  Accordingly, we see more meteors as dawn approaches.  Big city lights or the Moon can limit the meteors you see by dimming out fainter ones.  This August, however, the New Moon is on the 10th, giving us a skinny crescent on the 12th which sets long before the shower really gets going.  The main challenge, then, is to avoid city lights.

If skies that night are clear, our George Observatory will open Thursday night, August 12 at 9pm and remain open until dawn for observing the shower.  If you come out to George or go elsewhere, you’ll want to lie on your back (to see as much of the sky as at once as possible) and orient yourself towards the constellation Perseus.  (The shower is called the ‘Perseids’ because they seem to radiate from that constellation.)  Perseus rises in the northeast at dusk and is high in the north at dawn.

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The Great Planet Race

Published
by
James
on July 20, 2010
in Astronomy
. 0 Comments

During July and August 2010, you can watch a great planet race as Venus and Mars close in on and then pass Saturn. Observing this will also give you a sense of how the ancients, even thousands of years ago, could distinguish the planets from the stars and from each other.

Thousands of years ago, the earliest astronomers noticed that they could form patterns with the stars.  They also noticed that these patterns remained the same throughout their lives and even across generations.

In contrast to these “fixed stars,” there were seven “wandering stars.”  Consistent observation revealed that five points of light in the night sky shifted position noticeably from night to night.  After a year, even the slowest of these was clearly “out of place.”   The other two “wanderers” were the sun and the moon.  From the Greek word for “wanderer,” today we call these moving objects planets.  (The sun and moon were thus “planets” until we understood the solar system better.)

Cellarius ptolemaic system

With more careful observation, we can clearly distinguish the planets from one another using only the naked eye.  One of the planets far outshines all the others, and in fact outshines everything in the sky except the sun and moon.  Ancients named this one after the goddess of love and beauty–Aphrodite for the Greeks and Venus for the Romans.  Another planet has a distinctly reddish tint compared to all of the others, whose light is closer to pure white.  This one has therefore borne the names of gods of war, such as the Greek Ares and Roman Mars.

“Jupiter of Smyrna” currently residing
in the Louvre in Paris, France.


An important way to distinguish among the planets was to observe them when several were close together and to note which ones moved faster compared to others.  The fastest moving planet, the one that always passed up the others (unless it appears to stop and head the other way), received the name of the swiftest god.  For the Greeks, this was the messenger god Hermes, for the Romans it was Mercury.  On the other hand, there were two planets so slow that the motion was barely noticeable from night to night, but could be detected over months or years.  These two were considered rulers of heaven since they were the farthest away.  After all, ancients noticed that faraway objects, such as ships sailing at the limit of their vision, seemed to be going slower than similar objects close by.    The very slowest planet is also the dimmest; any other planet at its brightest outshines it.  The second slowest, on the other hand, outshines all stars at night and all planets except Venus.  Thus, the Greeks identified the slowest planet with the former, deposed ruler of heaven (Kronos/Saturn).  The planet which is brilliant despite its great slowness and distance was the true ruler of heaven (Zeus/Jupiter).

Now, you can go outside and make these same types of observations. In July 2010, face west at dusk to find three planets.  Venus is by far the brightest, outshining all the planets and stars.  Mars and Saturn are to the left and  slightly higher in the sky.  Although they aren’t nearly as bright as Venus, Mars and Saturn easily outshine all stars in their immediate vicinity and are therefore just as noticeable.  Mars is between Venus and Saturn and slightly below a line joining those two.

During the rest of July, Mars will close the gap on Saturn, until by July 31 it appears less then 2 degrees under the ringed planet.  Meanwhile, Venus will have closed to less than 8 degrees to the right of the pair.  Keep watching in August as Mars pulls ahead of Saturn while Venus begins to form a compact triangle with them both.  Venus is less than 3 degrees below Saturn on August 8 as it continues to gain on Mars.  Finally, Venus catches up to Mars and is less than three degrees below it on August 19.  By the end of August, the three planets have reversed their order; Venus has become the leftmost of the three, while Saturn will be on the right.

As you keep observing, you will also notice that Venus begins to slow down a little once it has “won” the race.  Also, it begins to move off of the imaginary line joining Mars and Saturn.  This is due to the geometry of our solar system.  Mars and Saturn are traveling slower than earth on their outer orbits.  Thus, Earth is leaving them behind and will pass on the far side of the Sun from them.  That’s why we see Saturn (in September) and Mars (in December) drop into the Sun glare.

Venus, on the other hand, is orbiting inside Earth’s orbit and is therefore going faster than Earth.  We’re seeing Venus come out from behind the Sun, and then around to our side of the Sun.  That’s why Venus seems to slow down–it’s starting to move towards the Earth.  Once Venus is on our side of the Sun, we see it move backwards (or retrograde) against the background stars.  In October, when Venus “laps” the Earth, we can’t see it at all.

Viewers with perfectly clear horizons who observe right at dusk may also glimpse Mercury.  The elusive Messenger is to the lower right of the other three planets and roughly in line with them.  Mercury won’t catch up to the other three however.  By August, Mercury will have come around to our side of the Sun, so we’ll see it head back towards the Sun’s glare before it aligns with Saturn, Mars, or Venus.

The King of Planets, Jupiter, sits this one out.  he makes a grand entry into the eastern sky at dusk this September, is up all night long on September 21, and dominates the evening sky throughout the fall.


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