Go Stargazing! May Edition

Creative Commons License photo credit: Elsie esq.

Saturn is now in the south southeast at dusk.  We are seeing its rings a little more edge on than earlier in the year.  In fact, Saturn’s rings won’t be this edge-on to us for another 15 years.  Saturn, like Earth, is tilted on its axis (at 26.7 degrees, Saturn’s tilt is a little greater than Earth’s).  Twice per Saturn orbit, then, about every 15 years, Saturn has equinoxes where the sun is aligned with Saturn’s equator.  Since the rings orbit the equator, this puts the sun (and the Earth) in Saturn’s ring plane.  Earth was exactly in Saturn’s ring plane on September 3, 2009 when Saturn was also on the far side of the sun and hard for us to see.  This month, Earth again approaches (but will not cross) Saturn’s ring plane.  That’s why the rings appear so thin in telescopes now. Learn more about the rings of Saturn in my latest blog post.

Venus keeps getting higher in the evening sky during May.  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 very 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.  However, during May, Mars remains brighter than average, and thus remains easy to see.  Look high in the west at dusk for a reddish point of light.

Jupiter is low in the southeast at dawn this month.  Look for it low in twilight as day begins to break.  It will be higher in the southeast by the end of the month.

In May, you can watch as the Dog Days begin!  We are in the Dog Days when the Dogs have vanished from the sky.  As May begins, Orion, the Hunter is clearly visible due west right after sunset.  To his left, aligned with Orion’s belt, is Sirius, the Dog Star, the brightest star we see at night.  Forming a triangle with Sirius and Orion’s brightest star Betelgeuse is Procyon, the Little Dog Star.  Throughout May, watch as Sirius appears slightly lower and lower to the horizon each night, until it is gone by May 31.  By mid-June, Procyon is gone as well.  When the Dogs are up only in the day, we’re in the Dog Days.

Meanwhile, spring stars are high in the south and east.  A distinct backwards question mark shape outlines the mane and forepaws of Leo, the Lion.  Three stars forming a right triangle rise underneath; 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 southeast, respectively, by dusk tonight.

星空下的汗腾格里峰 / Mt. Khan Tengri under Galaxy
Creative Commons License photo credit: livepine

As Orion and Sirius set, the plane of the Milky Way largely coincides with the horizon.  (At Houston’s latitude, the two planes are off by less than three degrees).  We are therefore looking straight out of the Milky Way plane when we look up early on a May evening.  Thus May evenings have fewer bright stars, as most of the brightest stars in the Milky Way plane are ringing the horizon.

Moon Phases in May 2010:

Last Quarter                 May 5, 11:15 pm

New                                  May 13, 8:05 am

First Quarter                May 20, 6:43 pm

Full                                    May 27, 6:07 pm

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.

Go Stargazing! August Edition

Jupiter is up all night long this month.  On August 14, the Earth passes between Jupiter and the Sun.  This alignment is called ‘opposition’ because it places Jupiter opposite the Sun in our sky, making it visible from dusk to dawn.  Tonight, Jupiter rises just before 9 p.m.—in late twilight.  It could take some time for Jupiter to clear trees or buildings around your observing site.  Soon, however, Jupiter will be already in the sky even as night is falling.  Face southeast and look for the brightest point of light there.  Early risers can still see Jupiter in the southwest before dawn.  Remember, Jupiter outshines everything in the sky except the Sun, the Moon, and Venus, so if you’re looking in the right direction, you can’t miss it.  

Venus is a dazzling morning star this month.  Look east right as day begins to break for the brightest thing unless the Moon is nearby.  Venus remains the ‘morning star’ for the rest of 2009.  Mars is a little higher in the east at dawn than it has been.  Still, it remains fairly dim.  Look for Mars above Venus in the east. 

is now low in the west at dusk, and will become difficult to observe by mid and late August.  The rings continue to appear thinner and thinner as Earth continues to align with Saturn’s ring plane, making the rings appear edge-on from our perspective.  On September 4, the Earth is exactly in Saturn’s ring plane, and the rings actually vanish from view!  It turns out, though, that Saturn is too close to the Sun in our sky on that date; the Earth will be about to pass on the far side of the Sun from Saturn.  No one can get a good look at Saturn this September.  Still, we can watch through our telescopes as Saturn’s rings appear thinner and thinner throughout August.  Since we’re seeing the rings edgewise, Titan and other moons have been passing in front of and behind Saturn’s disk.  This happens again on August 18, when Titan transits (passes in front of) Saturn’s disk.  By August 18, however, Saturn is so close to the Sun in our sky that it is only about five degrees high during late twilight and sets before night completely falls. 

Creative Commons License photo credit: Elsie esq.


The Big Dipper is high in the northwest on summer evenings.  From the Big Dipper’s handle, you can ‘arc to Arcturus.’  Arcturus, in the west at dusk, is the fourth brightest star we ever see at night and will be the brightest star in our evening skies during all of August. Continuing the curve of the Big Dipper’s handle past Arcturus, you can ‘speed on to Spica,’ a star lower in the southwest at dusk.  Spica is a stalk of wheat held by the constellation Virgo, the Virgin, who represents the harvest goddess.

Milky Way and a meteor?
Creative Commons License photo credit: madmiked

In the south as night falls is Antares in Scorpius, the Scorpion.  This is a red supergiant star about 700 times as wide across as our Sun.  To the Scorpion’s left, look for eight stars in the shape of a teapot.  These stars are the bow and arrow of Sagittarius, the Archer.  High in the east, the Summer Triangle dominates the evening sky.  The Triangle is up all night long until mid-August.  Vega is the brightest of the triangle’s three stars, followed by Altair in Aquila and Deneb in Cygnus.  Rising in the east on August evenings is the Great Square of Pegasus, heralding the upcoming autumn. 

Moon Phases in August 2009:

Full                                    August 5, 7:55 pm
Last Quarter                  August 13, 1:55 pm
New                                   August 20, 5:01 am
1st Quarter                     August 27, 6:41 am 

The Full Moon of August 5 almost enters the Earth’s shadow.  It does skirt the edge of the penumbra, in which the Earth partially blocks the Sun.  The resulting penumbral eclipse is scarcely noticeable at all, however.  When there is a central solar eclipse, as occurred last month in Asia, there are often penumbral (or very short partial) lunar eclipses two weeks before and after. 

Perseid Meteor
Creative Commons License photo credit: aresauburn™

The Perseid meteor shower peaks on the morning of August 12.  Our George Observatory will be open on the night of August 11-12 until dawn for observing the meteors.  Keep in mind that instead of the meteors running into the Earth, Earth is running into the meteors.  Thus, the leading edge of the Earth—the side going from night into day—sees more meteors.  This means you’ll see more meteors towards dawn than at dusk.  The Perseid shower averages about 2 meteors per minute each year, but this year a large waning gibbous Moon will hide many of those shooting stars from us.  If you observe the shower anywhere near a big city, light pollution will hide even more. 

The following Friday, August 14, is Members Night at the George Observatory.  The Perseid shower and the Members Night are events 63 and 64 of our Fun Hundred events to celebrate the museum’s 100th anniversary.

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.