Early Risers: You’re In For A Treat! June brings Blazing Comet & Lunar Eclipse

Are you an early riser and up before the crack of dawn?  If so, I encourage you to look up as you pick up that morning paper as there are two special treats in the June 2010 morning sky.

Comet McNaught
Creative Commons License photo credit: c.j.b

In January 2007, a brilliant comet, known as Comet McNaught dazzled observers in the Southern Hemisphere. Houstonians missed out on it, though, because of cloudy weather in our area during the brief time that comet was well placed for us. Now, in 2010, a different comet McNaught is becoming visible in our sky at dawn.

Robert H. McNaught, an astronomer at the Australian National Observatory, discovered this comet on September 9, 2009, using a telescope at Australia’s Sliding Spring Observatory.  McNaught, a prolific discoverer of comets, has discovered 44 comets (including this one) and is a co-discoverer of 12 others, for a total of 56.  This comet’s formal designation is C/2009 R1, where ‘C’ indicates a long period comet and ‘R’ indicates the time of year it was discovered.

Comet McNaught, though, is more than a ‘long-period’ comet.  Astronomers have determined that its eccentricity is greater than 1, meaning that its orbit has the shape of a hyperbola.  A hyperbolic orbit is the trajectory of a comet that passes near the sun once and never returns.  Once McNaught recedes from view, we’ll never see it again.

A hyperbolic orbit also means that McNaught has never been in the inner solar system before.  This challenges astronomers who want to predict how it will behave and just how bright it will become in our skies.  Already, McNaught is brighter than expected; many expect McNaught to become a naked-eye object by month’s end, especially for those able to observe at a dark site far from light pollution.  McNaught is now easily observable in binoculars.

This is a chart from Sky and Telescope, showing the path of Comet McNaught against the background stars.  Keep in mind that in June, the stars in this map rise in the northeast just before dawn.  McNaught continues to approach the sun until reaching perihelion on July 2, so we expect it to brighten until that date.  Unfortunately, a comet near perihelion is generally also close to the sun in our sky, and this comet is no exception.  Therefore, McNaught will also get harder to see as it brightens towards the end of the month.   After perihelion, McNaught is poorly placed for observers in the Northern Hemisphere.

17-08-2008 lunar eclipes
Creative Commons License photo credit: emrank

If you’re looking for the comet on Saturday morning, June 26, you might as well turn around and watch the moon set in partial eclipse.  Since the Moon is not precisely aligned with the Earth this time, it will not enter fully into the Earth’s shadow; it goes a little less than halfway in instead.  Still, from 5:17 a.m. until moonset at 6:25 a.m., you’ll notice a chunk of the moon’s upper right side missing.  (Actually, its the northern limb of the Moon that passes through the shadow.  The Moon’s northern limb is on the right as the Moon sets.)  The Moon is only about 10 degrees high when the eclipse starts, so you’ll need a southwest horizon clear of tall trees and buildings.  Note that the eclipse is still in progress at moonset; we will see less than half of it.  Folks far to our west will see a much longer event.

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.

Go Stargazing! January Edition

The full moon of Jan. 15 partially blocks the sun, causing an eclipse visible in Africa and Asia. Because it is close to apogee, the moon is too small in the sky to ever block the sun completely, and no total eclipse occurs. Instead, folks on a path stretching from Uganda and Kenya across the Indian Ocean to Sri Lanka, Burma, and China see an annular eclipse. The moon will appear to be completely inside the sun’s disk with a ring of sun around it.

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

At about 6 p.m. on Saturday, Jan. 2, the Earth came to perihelion. This means it was as close to the sun as possible—about 147 million km away (Earth is about 152 million km from the sun in July). This is not enough of a difference to influence our weather. Earth’s 23.5 degree tilt is much more important. Our North Pole is still tilted very much away from the sun and the sun still takes a very low path across our sky. Therefore, in spite of being as close to the sun as we’ll be all year, we’re going to be quite cold in Houston this week.

The latest sunrise of the year (at Houston’s latitude) occurs on Jan. 10. Earth is now just past perihelion, and has sped up a little in its orbit since it is a little closer to the sun. As a result, sunrise, local noon, and sunset have been happening a little later each day since early December. The noon sun is ever so slightly higher at noon each day since the solstice on Dec. 21, but as of today, the sun is still very close to its solstice height. Beginning Jan. 11, the noon sun’s greater height in the sky again becomes the dominant effect (as it is for most of the year). From then until June, sunsets are getting later while sunrises are getting earlier.

Jupiter is the brightest thing in the evening sky this month, except for the moon. You can easily see it by looking to the southwest.  Jupiter appears lower and lower to the horizon each January night.  By the end of the month, Jupiter sets just after 7 p.m.  At the end of February, Earth and Jupiter will be on opposite sides of the sun and Jupiter will therefore be invisible to us.

Mars has become an evening object.  It now rises in the east about 8 p.m. and will rise by dusk at the end of the month.  Mars already outshines all stars in the night sky except the very brightest (Sirius), and will continue to brighten throughout January.  On Jan. 29, Earth will pass between Mars and the sun, putting Mars in our sky all night long (this alignment is called opposition).

Saturn
Creative Commons License photo credit: Elsie esq.

Saturn is currently high in the south at dawn.  Although not as bright as Mars this month, Saturn  is also brightening as it approaches its own opposition in March.

Venus is behind the sun (at superior conjunction) on Jan. 11 and is therefore not visible this month.

The Great Square of Pegasus is in the west at dusk.  The star in its upper left hand corner is also the head of Andromeda.  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.  Since the Dipper is low and out of sight at dusk this month, Cassiopeia rides high.

Dazzling Orion is high in the southeast, reminding us that winter is here.  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.  Gemini, the Twins, are to Orion’s left as he rises (and to his upper left once they appear to the south).  Look for two stars of equal brightness less than 5 degrees (three fingers at arms’ length) apart.  These are Castor and Pollux, marking the twins’ heads.  High in the northeast is Capella, the sixth brightest star ever seen at night.

Moon Phases in January 2010:

Last quarter moon                 January 7, 4:41 am
New moon                                January 15, 1:12 am
First quarter moon                January 23, 4:53 am 
Full moon                                 January 30, 12:18 am

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.