Go Stargazing! June Edition

Size comparison of terrestrial planets (left to right):
Mercury, Venus, Earth, and Mars

Saturn is now in the south southwest at dusk.  Look just to the west of due south, about 2/3 of the way up from the horizon to the zenith, and you will see Saturn in the sky.

Venus remains high in the evening sky during June.  Face west at dusk and look for a point of light that outshines everything in the sky but the sun and the moon.

Mars is high in the evening sky, although not as bright as it was in winter.  Since January 29, Earth has been pulling ahead of Mars on its faster orbit.  As a result, Mars gets slightly dimmer each night for the rest of 2010.  As June opens, Mars is approaching the star Regulus in Leo from the right.  Mars is right next to the star on June 5, then pulls away from the star to the left after that.  Look high in the west at dusk for a reddish point of light.

Jupiter is in the south-southeast at dawn this month.  It outshines all stars in the sky, so it’s easy to find.

Spring stars are high in the south and west.  A distinct backwards question mark shape outlines the mane and forepaws of Leo, the Lion.  Three stars forming a right triangle are to its upper left; they mark Leo’s hindquarters.  The Big Dipper is as high as it ever gets in the north at dusk. You can extend the curve of its handle to ‘arc to Arcturus’ and then ‘speed on to Spica.’  These stars high in the east and south, respectively, by dusk tonight.  Arcturus, by the way, is the fourth brightest star we ever see at night, but the brightest one Americans ever see in all of June and July.

In the east, look for the enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair.   This triangle is up all night long in June and July, hence its name.  Scorpius, the Scorpion, is in the southeast at dusk.  Sagittarius, the Archer, known for its ‘teapot’ asterism, rises just after dusk on June 1, but is up by nightfall on June 30.

Moon Phases in June 2010:

Last Quarter                  June 4, 5:13 p.m.

New Moon                      June 12, 6:14 a.m.

First Quarter                  June 18, 11:30 p.m.

Full Moon                        June 26, 6:30 a.m.

It's ba-ack!
Creative Commons License photo credit: ronnie44052

The full moon of Saturday, June 26, will set in partial eclipse.  At 3:55 a.m., the moon first touches the penumbra of the Earth, the region where Earth partially blocks the sun.  The main event starts at 5:16 a.m., when the moon begins to enter the umbra, or the shadow itself.  The moon is not truly aligned with the Earth and sun this time, though, so it will not go all the way into the shadow.  This is why we have only a partial eclipse, with only the north (upper) limb of the moon in shadow.  The moon is still partly inside the umbra as it sets at 6:25 a.m.  (Although we no longer see it, the moon remains partially eclipsed until 8 a.m.)

This eclipse is merely a ‘warm-up’ for the spectacular total lunar eclipse we will have just after midnight on December 21.

At 6:29 a.m. on Monday, June 21, the sun is directly overhead at the Tropic of Cancer. Therefore, this day’s midday sun as high as possible in our skies.  This, then, is the moment of the summer solstice.  Those of us in the Northern Hemisphere enjoy more daylight on this day than on any other day of the year.

Partial Eclipse of the Eclipse: Report from Shanghai

In July 2009, I had a rare opportunity to travel with an HMNS sponsored tour group to the path of a solar eclipse. That eclipse occurred the morning of July 22, 2009, and was visible in Asia and the Pacific. Unfortunately, clouds marred the event as seen from our location just outside Shanghai. But since the clouds did not completely hide the eclipse, we were able to witness some of its effects.

Eclipsed? Not totally.
Creative Commons License photo credit: James Jordan

Solar eclipses occur when the Moon passes between the Sun and the Earth and casts its shadow on the Earth.  The shadow itself, called the umbra, is the region in which the Moon completely blocks the Sun.  Anyone in the Moon’s umbra experiences a total eclipse of the Sun.  As the Moon passes in front of the Earth, its shadow traces a path across the Earth’s surface; this is the ‘path of totality’.  To see a total solar eclipse, one must travel to a place on the path of totality.  As it happens, last month’s path covered parts of India, the Himalayas, China, and the open Pacific.

In an interesting coincidence, the Moon is about 400 times smaller than the Sun and about 400 times closer.  Thus, the Moon and Sun appear to be about the same size (just over 1/2 degree across) in our sky.  However, the Moon had been at perigee (closest approach to Earth) on July 21, making it slight larger than usual in our sky.  Further, every year in early July (July 3 in 2009) the Earth is as far as possible from the Sun (called aphelion).   These factors combined to make the New Moon of July 22 8%  larger than the Sun in our sky.  Thus, this is the longest eclipse of the 21st century, lasting 6 minutes and 39 seconds when seen on the centerline at local noon.

This was the latest eclipse in Saros cycle 136.  Astronomers in ancient Babylon noticed that similar solar and lunar eclipses recurred every 18 years, 10, 11, or 12 days, and 8 hours.  This corresponds to 223 lunations.  (One lunation is the period from one New Moon to the next–about 29.5 days).  The 10, 11, or 12 days depend on how many leap years are in the 18 year period.  In 1691, Edmund Halley applied the name ‘saros’ to this cycle, based the ‘SAR,’ a Babylonian unit of measure.  It turns out that the unit for keeping track of eclipses in Babylon was not the SAR, but Halley’s term stuck.  Cycle 136, then includes the eclipses of  July 11, 1991, June 30, 1073, and June 20, 1955.  Future eclipses in this cycle will occur on August 2, 2027, August 12, 2045, and so on.  As eclipses of cycle 136 occur further and further from aphelion, they won’t be quite as long as this year’s.  There won’t be a longer total solar eclipse until June 13, 2132.  That’s when a different saros cycle, #139, begins to occur near aphelion.

The Shanghai Tourism Administration estimates that over 13,000 overseas visitors traveled to Shanghai to watch the eclipse.  Along with hundreds of other eclipse chasers, our group left Shanghai proper to observe the eclipse from the Yangshan Deep Water Port, a small island southeast of the city itself.   To understand why, refer again to the July 2009 path of totality.  Drawn on the eclipse path on that map is a black Sun with small rays, indicating a point on the open water southeast of Japan.  This is the point of maximum eclipse, where the eclipse occurred at local noon and lasted the full 6 minutes and 39 seconds.  At other places on the path, totality was slightly shorter.  A few folks actually sailed the Pacific in order to be near that point.  We, however, opted for the convenience of observing on land.  Shanghai was the place in the path of totality closest to the point of maximum eclipse while still on the Asian mainland.

Also, note the blue line drawn down the middle of the path of totality.  Observing on that line, as opposed to the northern or southern edges of the path, gives you a longer eclipse.  Shanghai, although well within the path, is somewhat north of the blue centerline.  Moving from Shanghai itself to Yangshan island to the southeast put us closer to the centerline.  This gave us 5 minutes, 57 seconds of totality as opposed to about 5 minutes even in Shanghai.

eclipse 1
Photo from Shanghai, 2009 solar eclipse

As it turns out, there was another benefit from observing from Yangshan.  July 22, 2009 was rainy in Shanghai.  At Yangshan, however, it was simply overcast.  And just when we were beginning to think we’d miss the entire event, the clouds began to thin out in spots, allowing us occasional glimpses of the partially eclipsed Sun.

Unfortunately, those thinner clouds were not with us during totality.  We missed seeing the beautiful corona around the totally eclipsed Sun.  We could not see the planets and the brighter stars against the mid-day twilight sky.  And we could not watch the Moon’s shadow approach and then leave us  making shadow bands on the ground as it did so.  However, we did notice how much darker and cooler it got during totality.  After all, an overcast sky at night or in twilight is much darker than an overcast sky in broad daylight.  Cheers and whistles rose from Yangshan as darkness fell at 9:37 am and lasted until 9:43 am local time.

eclipse 2
Photo from Shanghai, 2009 solar eclipse

Literally seconds after totality was over, the clouds once again became thin enough for us to see the Sun through them.  As we watched the Sun come out of eclipse, we gave thanks for having avoided the rain and for being able to see as much as we saw, although we wished the clouds had thinned a little earlier to give us a glimpse of totality.

Would you like to have a similar experience?  Well, the path of the next total solar eclipse, on July 11, 2010, scarcely touches land at all, although it does pass over exotic Easter Island.  On November 13, 2012, totality is visible from northern Australia.

Can’t afford to leave the country to see an eclipse?  The Moon’s shadow crosses the United States on Monday, August 21, 2017.  The path of totality for that eclipse passes roughly from Salem, Oregon to Charleston, South Carolina.  How about a total eclipse right here in Texas?  Mark April 8, 2024, on your calendars.  On that date the Moon shadow first touches land near Mazatlan, Mexico, then sweeps right across the center of Texas before heading off to the northeast.  Folks in Dallas, Austin, and the western part of the San Antonio area see a total eclipse on that date; Houston experiences a deep partial eclipse.  The really young can look forward to May 11, 2078.  On that date, the Moon’s shadow passes just south of the upper Texas coast on its way to New Orleans and Atlanta.  Houstonians again experience a very deep partial eclipse.

The Moon’s shadow, then, will visit North America several times in the 21st century.  Maybe you can go observe the rare and beautiful spectacle of a solar eclipse, with better luck than I had in Shanghai. 

Go Stargazing! January Edition

Mercury and Jupiter begin this month together low in the southwest at dusk.  The two were side by side on New Year’s Eve; now Mercury is slightly higher in the sky than Jupiter.  Mercury is at greatest elongation (apparent distance from the Sun in our sky), and therefore highest above the southwest horizon, on January 4.  After that, is seems to double back towards the Sun and starts becoming harder to see.  Meanwhile, Jupiter just gets slightly lower each evening until it also drops into the Sun’s glare.  How deep into January can you follow them?

The departure of Mercury and Jupiter leaves Venus as the planet of January evenings.  Look west-southwest right as night falls for the brightest thing there except for the Moon, which is nearby at the beginning of the month. 

Two factors make Venus much higher in the sky now than in December or November.  First, Venus is at greatest elongation on January 14, just as Mercury is on the 4th.  Secondly, the plane of our solar system in our sky, called the ecliptic, intersects our horizon at a steeper and steeper angle each night as we go from the winter solstice to the spring equinox.  More and more of Venus’ apparent distance from the Sun is also height in the sky.  Also, Venus, on its faster orbit, is coming around to our side of the Sun (and will pass us in March).  Therefore Venus, which outshines everything in the sky except the Sun and the Moon, is getting even brighter this month as it approaches us. 

Saturn is now high in the southwest at dawn.  It will be rising in the east in late evening by month’s end.  Mars remains lost in the Sun’s glare this month.

12 segundos de oscuridad
Creative Commons License photo credit: Libertinus

Facing north, you’ll see five stars in a distinct ‘M’ like shape—this is Cassiopeia, the Queen.  Her stars are about as bright as those in the Big Dipper, and she is directly across the North Star from that Dipper.  In fall and early winter, while the Dipper is low and out of sight, Cassiopeia rides high.

Dazzling Orion rises in the east, reminding us that winter is on the way.  His belt points up to Aldebaran, the eye of Taurus, the Bull.  The Dog Stars Sirius and Procyon are below Orion in the east.  Sirius is the brightest star we ever see at night.  To Orion’s left as he rises are two stars of similar brightness less than five degrees apart.  These are Castor and Pollux, marking the heads of Gemini, the Twins.

Moon Phases in January 2009:

1st Quarter        January 4, 5:55 am
Full Moon          January 10, 9:27 pm
Last Quarter      January 17, 8:46 pm
New Moon         January 26, 1:55 am

Eclipse solaire
Creative Commons License photo credit: luc.viatour

The New Moon of January 26 blocks the Sun and thus causes an eclipse of the Sun.  The eclipse happens when it’s nighttime here, though; only those around the Indian Ocean see a partial eclipse.  What’s more, the Moon is near apogee (farthest distance from Earth) and appears slightly smaller in the sky.  Therefore, it can’t block the Sun completely, and people directly in the eclipse path see a small ring of the Sun around the Moon at maximum eclipse.  This type of partial eclipse is an annular eclipse.  The path of annularity is over the southern Indian Ocean; it does not touch land until it reaches Indonesia.

That same New Moon is also the second New Moon following the winter solstice.  Accordingly, it marks the Chinese New Year.  The Year of the Rat becomes the Year of the Ox on this date. 

Earth makes its closest approach to the Sun, called perihelion, at about 6pm on Saturday, January 3.  The Earth is about 98% of its average distance from the Sun (about 93 million miles).  Aphelion is on July 3, when Earth will be at 101.6% of its average distance from the Sun.  This is not enough of a distance to affect our seasons. 

Rangitoto @ Dawn
Creative Commons License photo credit: Chris Gin

The latest sunrise of the year occurs on the morning of January 10.  We are still close enough to the winter solstice that the Sun’s apparent path across the sky on January 10 is only slightly higher than on December 21.  Meanwhile, Earth has just passed perihelion a week earlier.  As a result, the Earth is moving a little faster than usual. 

The effect isn’t much (Earth’s orbit is nearly circular), but it’s enough to make both sunrise and sunset a little later each day this month and next.  With the Sun’s apparent height in the sky not changing that much until late January, the small effect of Earth’s acceleration near perihelion dominates.  Since most of us sleep through sunrise and witness sunset, the days seem be slightly lengthening much more than the actually are in early January.

Want to Learn More About Astronomy?
Read about the Big Bang and the timeline of the universe.
Learn how the days of the week got their names.
Discover the origin of Halloween.

Olympics withdrawal got you down?

Birds' Nest at Night
Creative Commons License photo credit: chumsdock

Are you suffering from Olympics withdrawal? Take your own travel adventure to China with the Houston Museum of Natural Science.

In less than a year, you can travel to China to see the most famous attractions of the country AND the longest total solar eclipse of the century.

The Olympics have shown us the new China – historic, modern and beautiful. The Houston Museum of Natural Science will explore its wonders during our trip to see the total solar eclipse in Shanghai next summer.

The trip includes three days in Beijing with time to climb the Great Wall, visit Tienanmen Square, the Forbidden City, the Temple of Heaven, the Summer Palace, and the most famous Olympics venues, including the Bird’s Nest and Water Cube.

The trip also includes Xi’an with its Terra-Cotta Warriors and Wild Goose Pagoda followed by a trip south for a Yangtze River cruise, ending at the Three Gorges Dam, as well as sightseeing in Shanghai.

Eclipsed? Not totally.
Creative Commons License photo credit: James Jordan

But the highlight and final event is the total solar eclipse, with the dark new moon passing in front of the sun, blocking all but its beautiful outer atmosphere from our view for six full minutes. From a special location near Shanghai, we will watch this rare celestial event, occurring over one of the most populous and modern cities in the world.

If you have any questions about this historic event or the trip we’re planning to witness it, please leave me a comment on this post.

(Can’t wait until July? Some of China’s most spectacular archaeological treasures – the Terra Cotta Warriors – are coming to Houston this May.)