Go Stargazing! August Edition

Saturn is the only planet visible to the naked eye at night this August.  Face southwest at dusk and you’ll see Saturn near a star of similar brightness—Spica in Virgo.  Saturn is a bit to the right of Spica as you face southwest.   The ringed planet remains well placed for evening viewing and remains in the night sky until late September 2011.

Hubble Images Suggest Rogue Asteroid Smacked Jupiter
Creative Commons License photo credit: NASA Goddard Photo and Video

Mars and Jupiter are in the pre-dawn sky.  Jupiter, set against a background of very dim stars, dominates the southeastern pre-dawn sky and is due south at dawn by the end of the month.  Mars is dimmer and much lower in the east northeast.  It has fully emerged from the sun’s glare and will brighten slightly each morning. Venus is now out of sight.  Superior conjunction (alignment on the far side of the sun) is on August 16.

The Big Dipper is to the left of the North Star, with its handle pointing up.  From that handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars are in the west and southwest at dusk.  Antares, brightest star of Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius to its left.  Meanwhile, the Summer Triangle is approaching the zenith.  The stars of summer now dominate the evening sky.  In late evening, you can watch the Great Square of Pegasus rise in the east.

Moon Phases in August 2011:

1st Quarter                     August 6, 6:08 a.m.

Full Moon                       August 13, 1:57 p.m.

Last Quarter                  August 21, 4:56 a.m.

New Moon                      August 28, 10:03 p.m.

The annual Perseid Meteor Shower peaks this year on Saturday morning, August 13.  Unfortunately, the moon (full on the 13th) hides all but the very brightest meteors and thus spoils the show.  If you want to see just how many Perseids can outshine the moonlight, the best hours are from roughly 2 a.m. to dawn.

Go Stargazing! July Edition

Saturn is the only planet visible to the naked eye in the evening skies of July, 2011.  Face south-southwest at dusk, and you’ll see Saturn near a star of similar brightness—Spica in Virgo.  Saturn is a bit to the right of Spica as you face southwest.   The ringed planet remains well placed for evening viewing, and remains in the evening sky until late September 2011.

Hubble Images Suggest Rogue Asteroid Smacked Jupiter
Creative Commons License photo credit: NASA Goddard Photo and Video

Mars and Jupiter are now higher in the pre-dawn sky.  Jupiter, set against a background of very dim stars, dominates the eastern sky at dawn.  Mars is dimmer and much lower in the east northeast.  It has fully emerged from the sun’s glare, and will brighten slightly each morning.  Venus is now out of sight, as it is passing around the far side of the sun from our perspective.

The Big Dipper is above the North Star, with its handle pointing up.  From that handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars are in the southwest at dusk.  Leo, the Lion, sets in the west at dusk.

Antares, brightest star of Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius rising behind it.  The Summer Triangle has fully risen in the northeast.  The stars of summer now dominate the evening sky.

Moon Phases in July 2011:

New Moon                       July 1, 4:02 p.m.

1st Quarter                     July 8, 9:09 p.m.

Full Moon                        July 15, 3:12 p.m.

Last Quarter                  July 23, 6:48 a.m.

Winter Solstice Lunar Eclipse
Creative Commons License photo credit: Bruce McKay~YSP

The new moon of July 1 partially blocks the sun, but only as seen from the Antarctic.  No one will get to see a total eclipse because the moon’s full shadow, or umbra, passes just below the Earth.

As we celebrate our independence this July 4, Earth will be at aphelion (at its greatest distance from the sun).  The precise time is 10 a.m.  Perihelion, the Earth’s closest approach to the sun, occurs in January.  Earth has perihelion and aphelion because its orbit is not a circle but an ellipse with an eccentricity (out-of-roundness) of about 1.6%.  Such a small variation, however, exerts no significant influence on our seasons, as you can determine for yourself by stepping outside.  The 23.5 degree tilt of Earth’s axis, on the other hand, is a much more dominant effect.  The very high midday sun of July ensures long days and baking heat in Houston and across much of the Northern Hemisphere.

By popular demand, our George Observatory will open to the public Fridays and Saturdays this summer (except July 8, due to a prior booking).  The Discovery Dome, our traveling planetarium, will be set up each of these Fridays to show films throughout the evening.

Go Stargazing! June Edition

Saturn
Creative Commons License photo credit: Elsie esq.

Saturn is the only planet visable to us at night this June.  Face south at dusk, and you’ll see Saturn near a star of similar brightness — Spica in Virgo.  Saturn is significantly higher in the sky than Spica and a bit to its right as you face south.   The ringed planet is now well placed for evening viewing, and remains in the evening sky until late September 2011.

Mars and Jupiter are now higher in the pre-dawn sky.  Jupiter, set against a background of very dim stars, dominates the eastern sky at dawn.  Mars is dimmer and much lower in the east northeast.  It has fully emerged from the sun’s glare, however, and will brighten slightly each morning.  Venus does not rise until morning twilight.  Look for it very low in the east northeast as day breaks.

The Big Dipper is above the North Star, with its handle pointing up.  From that handle, you can “arc to Arcturus” and then “speed on to Spica;” those stars are in the south at dusk.  Leo the Lion, is high in the west at dusk.

Antares, brightest star of Scorpius, the Scorpion, is in the southeast, with the ‘teapot’ of Sagittarius rising behind it.  The Summer Triangle has fully risen in the northeast.  The stars of summer are here. 

Moon Phases in June 2011:

New Moon                    June 1, 4:02 p.m.

1st Quarter                  June 8, 9:09 p.m. 

Full Moon                     June 15, 3:12 p.m.

Last Quarter               June 23, 6:48 a.m.

Red Light...
Sunset
Creative Commons License photo credit: Kıvanç Niş

The full moon of June 15 passes through the Earth’s shadow, causing a total eclipse of the Moon. Unfortunately, we miss out on that one, too, as the eclipse occurs during our daylight hours.  Anyone in the Eastern Hemisphere, though, can observe a central (and therefore especially long) total eclipse of the moon. 

At 12:17 p.m. on Tuesday, June 21, the sun is directly overhead at the Tropic of Cancer, the farthest point north where this is possible.  This makes the midday sun as high in our sky as possible and gives us more daylight than on any other day of the year.  This moment is, therefore, the summer solstice.  However, the earliest sunrise for us is the morning of June 11 and the latest sunset is on June 30.  Those of us who sleep through sunrise and witness sunset may get the impression that the days are lengthening all the way to the end of the month.

By popular demand, our George Observatory will open to the public not only on Saturdays, but also all Friday nights in June and July (except July 8).  The Discovery Dome, our traveling planetarium, will be set up each of these Fridays to show films throughout the evening.

Chak Ek’

Page 49 of the Dresden Codex

Have you had a chance to come out and see our newest planetarium show, 2012:Mayan Prophecies?  If so, you’ve enjoyed a fascinating glimpse into an ancient culture known for its astronomy.

The Dresden Codex

Consider, for example, the Dresden Codex, the oldest book known to be written in the Americas.  The best preserved of four ancient Maya writings, this 11th or 12th century document found its way to an owner in Vienna; Johann Götze of the Royal Library at Dresden bought it in from that person in 1739.  (The writing was probably first sent into Europe by Hernán Cortés, conquistador of Mexico.)

The Dresden Codex features tables of eclipses, full and new moons, as well as the times of solstices and equinoxes.  Conjunctions (close alignments of planets in the sky) are noted, as are the times when each planet rises just before or just after the sun.  The Codex devotes six pages to measurements of the positions of Venus.

Chak Ek’

The emphasis on Venus, or Chak Ek’ to the Maya, distinguishes ancient Maya astronomy from that practiced by other ancient cultures.  Of course, people in civilisations all over the world noticed Venus, which outshines everything in the sky except the sun and the moon.  However, other cultures did not consider cycles of Venus as important for time keeping. Let’s look at how Maya astronomers could use Venus as a marker of time.

First, some basic facts about Venus and its orbit.

Venus is the second planet from the sun; Earth is the third. As result, Venus’ orbit is completely inside Earth’s and we see the whole orbit in ‘front’ of us, so to speak. As of May 2011, Venus is in the morning sky, where it has been since November 2010. This means that for the past six months, Venus has been ahead of us on its faster, inner, orbit.

However, we’ll soon see Venus pass around the far side of the sun, making it invisible to us for about a month and a half this summer.  By fall 2011, Venus will have emerged from behind the sun, such that it appears to the sun’s left in our sky.  This makes Venus an evening star, appearing over the western horizon at dusk.  Venus remains an evening star through spring 2012, while it gradually catches back up to Earth, coming back around to our side of the sun. On June 5, 2012, Venus catches back up to us and ‘laps’ the Earth on its faster orbit.  Thus we’ll see Venus quickly drop out of the evening sky in late May and reappear in the morning sky by mid-June.  Venus then remains in the morning sky until it heads around the far side of the sun by March 2013, and the process repeats.

Global radar view of Venus.
Photo taken by NASA

A Venus Cycle

One Venus cycle, as described above, takes 584 days.  Also, as it turns out, Venus completes 13 orbits around the sun in almost exactly eight years.  On a given date in 2011, for example, Venus is where it was in the sky on the same date in 2003, within two days.  These facts enabled the Maya to keep a regular calendar of Venus’ appearances.  For the Maya, each Venus cycle began with Venus’ entry into morning sky, rising just before the sun.  Called the heliacal rising of Venus, this is the moment when Venus is on our side of the sun, having just ‘lapped’ Earth and pulled ahead on its faster orbit.

Maya astronomers also noted Venus’ emergence into the evening sky, but considered that less significant.  After all, Venus becomes an evening star only gradually, taking over a month to emerge from the sun’s glare.  It is also dimmer than average at this time because it is on the far side of the sun from us.  On the other hand, Venus enters the morning sky quite quickly and dramatically, appearing noticeably higher each morning for several days.  And since Venus is closest to us at that time, it is also brighter than average.  Upon observing a heliacal rising, Maya astronomers knew the next would occur 584 days later.  And they knew to expect another such rising of Venus during the same season about eight years later.

The Only Planet Named for a Goddess

Due to its brillance, cultures around the Mediterranean associated Venus with love and beauty.  That’s why Venus is the only planet named after a goddess.  At one time, the Greeks distinguished the evening star Hesperus (Latin ‘Vesper’) from the morning star Phosphorus (Latin ‘Lucifer’), but they were both names for Venus.

Maya also distinguished the evening star (Lamat) from the morning star (Ah-Chicum-Ek’).  For the Maya, either appearance of Venus was a harbinger of evil–particularly the morning star.  This made Venus’ sudden appearance at dawn a good omen for someone wishing to wreak destruction.  Accordingly, Maya often scheduled attacks on rival cities to coincide with the heliacal rising of Venus.  One such attack, which the Maya called a ‘Star War,’ is depicted in our show.

Looking For Venus Today

If you want to observe Venus today (May 2011), you need to rise before dawn and face east.  An interesting gathering of four planets, in progress for much of the month, still continues.  As I write this, Venus and Mercury have passed Jupiter and are approaching Mars.  Venus and Jupiter are about eight degrees apart with Venus to the lower left.  They far outshine everything else but the sun and the moon, so those two planets are easily noticeable well into twilight.  Mars and Mercury appear to either side of Venus  and are much dimmer.  Right now, Mercury is to the lower right of Venus with Mars to the right and a bit above Venus. Today, Venus is within one degree of Mars.  Mars is above Venus, Mercury below.  The alignment of Mercury, Venus, and Mars was closest on the morning of May 21.

After this, Mercury quickly exits the scene while Venus gets lower and lower in the pre-dawn sky throughout June, until it is lost inthe sun’s glare by July.  2012, however, offers some spectacular views of Venus.  In spring 2012, Venus appears as high as possible in the evening sky (as it did in 2004 and will do again in 2020). That particular evening apparirion ends June 5, 2012, as Venus aligns so well with the Earth and sun that it appears as a dot on the sun’s disk.  That transit of Venus will be the last such event in the lifetime of anyone alive today.

Hopefully, none of this will be taken as a sign to sacrifice or invade others.