The ‘blood moon’ in Houston: Stay up late at the George for a stunning celestial show

A total eclipse of the Moon will occur very early Tuesday morning, April 15. Houstonians will be able to see the whole event, which begins just before 1 a.m. You’ll be able to see the evening’s cosmic events unfold even under city lights, but if you’d like a more detailed (and dare I say captivating) look at the eclipse, the George Observatory will be open all night long!

Lunar eclipses occur when the full Moon moves into the Earth’s shadow. The first part of the Earth’s shadow that the Moon will encounter is the penumbra. The penumbral shadow’s faintness means that sharp-eyed observers will notice only a slight dimming of the Moon between 11:55 p.m. on Monday night and 12:58 a.m. Tuesday. The Moon moves into the darkest part of the earth’s shadow, the umbra, at 12:58 a.m., and will be totally eclipsed by 2:06 a.m.

The Moon’s brightness during a total eclipse depends on the amount of dust particles in the atmosphere. A large amount of dust from a volcanic eruption, for example, can make the totally eclipsed Moon almost invisible.

With little dust in our atmosphere, the Moon glows reddish-orange during totality.

This is because only the Sun’s red light comes through the Earth’s atmosphere and falls on the Moon even while it is in the Earth’s shadow. As the diagram shows, the Moon will pass through the southern part of the shadow, for about 78 minutes of totality. As a result, the northern limb, closer to the center of Earth’s shadow, will appear darker.

We’ll see our next total lunar eclipse in Houston just before dawn on October 8, 2014 (the second of four occurring between 2014 and 2015!).

For more on how lunar eclipses work, watch the video below from NASA and USA Today.

Go Stargazing! June Edition

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...
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.

Coming Soon: Total Eclipse of the Moon! [Dec. 21, 2010]

A total eclipse of the moon will occur very early Tuesday morning, Dec. 21, 2010. Houstonians will be able to see the whole event, which begins shortly after midnight.  If you happen to be traveling for the holidays, don’t worry – our entire continent has a full view of this eclipse.

When will the Lunar Eclipse Occur?

Note the timing, which might throw off some people.  The night we’re talking about is Monday night, December 20, and Tuesday morning, December 21.  For people in Houston, the eclipse starts at about 12:30 a.m., so the date is December 21.  If you go out on the night of the 21st looking for this event, you will have missed it by one day.

All times are listed in CST:

Stage Tuesday, Dec. 21
Partial Eclipse 12:32 a.m.
Totality Begins 1:40 a.m.
Mid-eclipse 2:17 a.m.
Totality Ends 2:54 a.m.
Eclipse Ends 4:01 a.m.

Why do Lunar Eclipses Occur?

Lunar eclipses occur when the full moon moves into the Earth’s shadow.  The orbits of the Earth and moon are not exactly in the same plane; the moon’s orbit is inclined to ours by about 5 degrees.  This may not seem like much, but it is enough to make the full moon miss the Earth’s shadow most of the time.

About twice a year, the full moon is close enough to Earth’s orbital plane to encounter the shadow rather than passing above it or below it.  Even at that, a slightly imprecise alignment may cause the moon to skirt the edge of the shadow (resulting in only a partial eclipse) or even just the penumbra (no noticeable change for us).  For example, on the morning of June 26, the moon never fully entered Earth’s shadow, and we saw it set in partial eclipse.

Finally, when the moon does go all the way into the Earth’s shadow, we see the event only if it happens during our nighttime, and if skies are clear.  During the last total lunar eclipse visible in America, on February 20, 2008, we were clouded out in Houston.  Given all of these factors, the opportunity to watch a lunar eclipse is quite special.  Let’s all hope the weather cooperates and we all can take some time to enjoy this spectacular sight.

What to Watch For: Observing An Eclipse

Lunar Eclipse March 2007
Creative Commons License photo credit: foxypar4

Observing the eclipse is quite simple; everyone who sees the moon sees the eclipse. Unlike the sun, the moon presents no danger to our eyes when observed directly. No special observing equipment is necessary. Unlike dimmer objects such as meteors, the moon shows up clearly even among bright city lights. You can enjoy the eclipse from your backyard, even if this is in the middle of Houston.

As the Earth blocks sunlight and casts a shadow across space, we can define two regions.  The umbra is the region of space in which Earth completely blocks the sun.  The penumbra is the region of space in which Earth only partially blocks the sun.

The first part of the Earth’s shadow that the moon will encounter is the penumbra. The penumbral shadow’s faintness means that even sharp-eyed observers will notice only a slight dimming of the moon between 11:28 p.m. on Monday night and 12:32 a.m. Tuesday. The moon moves into the darkest part of the earth’s shadow, the umbra, at 12:32 a.m, and will be totally eclipsed by 1:40 a.m.  Totality lasts 73 minutes because once in, the moon takes until 2:53 a.m. to cross to the other side of the umbra.  The moon then takes just over an hour to re-emerge from the umbra.  By 4:01 a.m., the moon has moved out of the Earth’s shadow, and the eclipse is over.

How Bright will the Eclipse Be?

Eclipse burning bright
Creative Commons License photo credit: ericskiff

The moon’s brightness during a total eclipse depends on the amount of dust particles in the atmosphere. A large amount of dust from a volcanic eruption, for example, can make the totally-eclipsed moon almost invisible. With little dust in our atmosphere, the moon glows reddish-orange during totality. This is because only the sun’s red light is bent enough by the Earth’s atmosphere that it lands on the moon even while it is in the Earth’s shadow.

As this diagram shows, the moon will pass through the northern part of the shadow, for about 73 minutes of totality. As a result, the bottom (southern) limb, closer to the center of Earth’s shadow, will appear darker.

Last Chance to See A Lunar Eclipse?

There are two lunar eclipses in 2011, but Houstonians won’t get a good look at either one.  The eclipse of June 15, 2011 occurs while we’re having daytime.  On the morning of December 10, 2001, an eclipse gets underway just as the moon sets for us.  In Houston, we see only the first 15 minutes of that eclipse.  (Observers farther north and west see more.)  We won’t see our next total lunar eclipse in Houston until just after midnight on April 15, 2014.

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.