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! January Edition

Jupiter, now in the west at dusk, dominates this month’s evening skies.  It outshines all stars in the sky, so it’s easy to find.  Face west southwest at dusk and look for the brightest thing there.

Venus remains a dazzling morning star.  Face southeast at dawn and you can’t miss it.

Saturn is in the south southwest at dawn, above the much brighter Venus.

Mars is still lost in the sun’s glare; it will remain invisible to us all winter as Earth passes around the far side of the sun from it.

The Great Square of Pegasus sets in the west, while brilliant winter stars shine in the south.  Orion, the Hunter, is almost due south.  His two dogs, represented by Sirius and Procyon, are to his left.  Above Orion is Taurus, the Bull with Aldebaran as its eye. Gemini, the Twins, are to Orion’s upper left.

Moon Phases in January 2011:

New Moon                              January 4, 3:03 a.m

1st Quarter                             January 12, 5:32 a.m

Full Moon                               January 19, 3:22 a.m.

Last Quarter                          January 26, 6:58 p.m.

The new moon of Tuesday, January 4, partially blocks the sun, causing a partial solar eclipse.  This event occurs during our nighttime, however; the eclipse is visible only in Europe, western Asia, and northern Africa.

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

At about 1 p.m. on Monday, January 3, the Earth is as close to the sun as it will get all year. In other words, Earth is at perihelion. Earth’s orbit is not a perfect circle but an ellipse, so its distance from the sun varies between about 147 million kilometers in January and 152 million kilometers in July. This variation is too small to affect our seasons; the effect of Earth’s 23.5 degree title on its axis dominates it. That’s why it’s colder now than in July. The actual moment of perihelion varies each year between late on January 1 and early on January 5.

At Houston’s latitude, the latest sunrise of the year occurs Friday, January 10.  Of course, days have been lengthening since the solstice, which makes sunset later and sunrise earlier.  However, Earth is still going a little faster than average on its orbit, since it is just past perihelion (its closest approach to the sun).  This causes sunrise, local noon, and sunset to occur slightly later each day.  Until mid-January, we are still close enough to perihelion that the second effect actually predominates.  As a result, sunset gets a little later during early January even while the days are getting longer.

Go Stargazing! November Edition

Jupiter is the brightest planet or star in the evening sky this month.  Face south and look for the brightest point of light there.  If you’re looking in the right direction, you can’t miss it. Jupiter can currently be found inside the constellation Capricornus.

Venus begins to wrap up its stint as morning star this month, as it’s now much lower in the pre-dawn sky.  Look southeast right as day begins to break for the brightest thing (other than the Moon.)  Venus remains the ‘morning star’ for the rest of 2009.  Mars is now almost overhead at dawn. It is also brightening as the Earth approaches it. Saturn is now also visible in the morning sky, but it is not as bright as Venus.

Star gazing
Creative Commons License photo credit: Paul Jerry

The Big Dipper happens to be to the lower left of the North Star at dusk this month; you’ll need a clear northern horizon to get a good look at it.  Sagittarius, the Archer, known for its ‘teapot’ asterism, is in the southwest.  Look for the enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair, high in the west.   As familiar summer patterns shift to the west, the constellations of autumn take center stage.  The Great Square of Pegasus is high in the east 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.  In fall, while the Dipper is low, Cassiopeia rides high.

Our Milky Way Galaxy..
Creative Commons License photo credit: Sir Mervs [oh i see..]

You will notice that November evening skies are generally dimmer than skies in summer or winter.  This is because we are facing out of the galactic plane.  Our Milky Way is quite flat—about 100 times as wide as it is thick.  As a result, most stars, including most of the brighter stars, are near the plane of the Galaxy.  We therefore see fewer bright stars when looking perpendicular to this plane, as we do when we face south on November evenings.

Our Galaxy is part of a Local Group of about 40 galaxies.  This group, in turn, is on the edge of the Virgo Supercluster of galaxies.  It turns out that when we look up in November, we have our backs to the center of that huger supercluster and are facing our own Local Group.  Thus, other members of that group, such as the Andromeda Galaxy and the Triangulum Galaxy, are high in the sky.  On May evenings, when we again look out of our galaxy plane, we’ll be facing the center of the Virgo Supercluster and have our backs to our own Local Group.

Moon Phases in November 2009:

Full                                     November 2, 1:14 pm
Last Quarter                   November 9, 9:57 am
New                                   November 16, 1:13 pm
1st Quarter                     November 24, 3:38 pm

Today, the just-past-full Moon will pass very close to a star cluster called the Pleiades.  At 9:11 p.m. and again at 10:11 (CST), it will briefly occult (hide) a couple of its stars.