Tag Archives: eclipse

Go Stargazing! June Edition

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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.

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

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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.

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

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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

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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.