Extended hours at the George this weekend make for optimum Milky Way consumption

The galaxy, not the candy, of course!

Pleiades Rising
photo by DerekSteen

This Friday night, the George Observatory will offer one of the first summer viewings of the Milky Way — with extended hours from 5 to 11 p.m. And as with the George’s usual Saturday night viewings, research telescopes will also be available to stargazers along with the planetarium.

Stay starstruck the following day, when Rocket Day launches with virtual missions to the Moon in our Challenger Center on Saturday morning, and Family Space Day takes you to the Moon with NASA on Saturday afternoon.

In short: Join us for a family-friendly day of fun!

For more information and directions to the George Observatory, click here.

 

The stars at night are big and bright, deep in . . . New Zealand?

Editor’s note: This blog is one of a series of travelogues by HMNS VP of Astronomy Carolyn Sumners, sent from the two-week solar eclipse viewing trip she led to the South Pacific. Astrophotography by Gary Young.

The stars of the southern hemisphere are fantastic, with the brilliant Milky Way stretching from near the hunter, Orion, in the North to Crux, the Southern Cross, in the South.

This predawn image is a time exposure with a Canon Mark II camera and a fisheye lens, taken from our hotel lawn in Queenstown, New Zealand, looking out over Lake Wakatipu. Even with some glare from the hotel and from Queenstown to the East, the predawn sky is remarkably dark. This exposure approximates what we could see as we faced south.

Examining the stars from southern Australia with Dr. Carolyn SumnersNew Zealand has a total population less than 5 million, which guarantees much less light pollution, even close to a city. Also, the southern Milky Way is much richer and more easily seen than the Milky Way near the North Star.  In New Zealand, we trade views of the Big and Little Bears for the Southern Cross and the nebulae around it. This image is a close-up of the southern Milky Way in the early evening as we started stargazing. Notice the dark areas in the Milky Way. The Inca saw animals in these dark dust clouds.

Examining the stars from southern Australia with Dr. Carolyn SumnersWhile observing through two telescopes, we placed our third telescope, a Takahashi FS60Q, on a small portable Sky Patrol equatorial mount that would track the stars — adjusting for the Earth’s rotation. We were able to do time exposures of up to a minute without guidance and we captured incredible views of the Orion Nebula, the Omega Centauri globular cluster, the Large and Small Magellanic Clouds and the Carina Nebula.

Examining the stars from southern Australia with Dr. Carolyn Sumners
Large and Small Magellanic Clouds

Through a telescope we saw the shapes of these clouds and clusters, but not the rich colors and textures captured in these images. The Orion Nebula is a stellar birth cloud with new stars still forming from the gas and dust. The Carina region has young stars and the dying supergiant Eta Carinae.

Examining the stars from southern Australia with Dr. Carolyn Sumners
Eta Carinae nebula

Omega Centauri is the brightest globular cluster in Earth skies with 5 million stars. The Large and Small Magellanic Clouds are satellite galaxies of our Milky Way galaxy. We can see the Orion Nebula easily from Houston. The other magnificent objects are best seen from below Earth’s equator.

Examining the stars from southern Australia with Dr. Carolyn Sumners
Orion Nebula

It’s a wonderful sky down under.

The Celestial Sea

As you look up into a November sky right at nightfall, you may notice fewer bright stars than at other times of year. No, it’s not just the glare from Houston hiding most of the stars from view–there really are fewer bright stars in the November evening sky than in, say, February or August. To understand why, you need to understand the shape of our galaxy itself.

death cab for cutie:I'll follow you into the dark
Creative Commons License photo credit: visualpanic

Our galaxy, the Milky Way, is a barred spiral galaxy.

Evidence indicates that the Milky Way, like many large galaxies, has a massive black hole at its center. A radio source designated Sagittarius A* could be the black hole itself. (The asterisk is part of the name, which is “Sagittarius-A-star”). Surrounding this black hole is a central bulge where older (and thus redder) stars predominate.  The Bulge of our galaxy is not fully spherical but instead forms a bar a few thousand light years long.  Branching out from this bulge are spiral arms which contain younger (bluer) stars and dust clouds out of which brand new stars form.  Our solar system is about 26,000 light-years from the center to the edge, on the inside edge of the Orion Arm.  The Orion Arm, in turn, is but a spur of the much longer Perseus Arm.  The Milky Way is quite flat–over 100,000 light years wide but only 1,000 light years thick.

The flatness of the galaxy means that most of its stars are near a certain plane in space.  Of course, the galaxy is much thicker than our solar system, so we see our stellar neighbors suurounding us on all sides.  The rest of the galaxy, extending off into the distance, appears to us as a hazy blur in the background, with individual stars (those fairly close to us) in the foreground.  That hazy blur looked like spilled milk to the ancient Greeks, thus the name ‘Milky Way.’  We see more stars near that plane than far from it.

What does this have to do with the dimness of a late November sky at dusk?

Imagine observing our flat galaxy from our vantage point on Earth. When we face into the galactic plane, we see more bright stars, because there are more stars in that direction.  When we face above or below that plane, we see fewer bright stars.

Face west at dusk in late November and early December, and you’ll notice an enormous triangle of three bright stars, all bright enough to appear even in skies lit by Houston.  These stars from the Summer Triangle, so called because it is up all night long from June through mid-August.  This Triangle is also directly in the plane of the Milky Way.  The constellation Sagittarius, which marks the center of the Galaxy, sets just after the Sun this time of year.  Therefore, if you trace a path approximately from the  point of sunset through the Summer Triangle, over to five stars in an ‘m’ shape in the North (that would be Cassiopeia, the Queen), and then over to the northeastern horizon.  This is the plane of the Milky Way across late autumn skies at dusk .

Turn to the south, and you face below the galactic plane (as we’ve arbitrarily defined ‘above’ and ‘below’).  Here is a vast region of sky almost void of bright stars.  One exception is Fomalhaut, low in the southeast at dusk tonight.  Also, Houstonians with a very clear southern horizon can see Achernar very, very low in the south on December evenings.  But that’s about it.  There are many fewer bright stars in this direction than towards the Summer Triangle.  By the way, the brilliant object in the east at dusk tonight, and high in the southeast as dusk in December, is Jupiter. It doesn’t count as a bright star for this sector of the sky.

The Celestial Sea

When ancient Mesopotamians looked up into the dim skies you see at dusk tonight, they imagined the Persian Gulf south of them extended up into the sky, forming a ‘Celestial Sea’.  They therefore placed many water-themed constellations in this part of the sky.  Zodiacal constellations here include Pisces, the Fish, and Aquarius, the Water-Carrier.  Even Capricornus, the Goat, has the tail of a fish because he originally represented Ea, the ancient Babylonian god of the waters.  Under Pisces is the sea monster Cetus, while Piscis Austrinus, the Southern Fish, drinks the water that Aquarius pours.  Eridanus, the River, rises in the southeast, flowing from Orion’s foot into this vast ‘sea.’

predawn
Creative Commons License photo credit: paul (dex)

Contrast this vast, dim region with the much brighter swath of stars that rises in the east later this evening (9-10 pm in late November, earlier in December).  This region of sky includes the brilliant pattern Orion, the Hunter, as well as Sirius, the brightest star we ever see at night.    When these stars rise, we are beginning to face back into the plane of our galaxy, this time looking into our own arm of galaxy at the stars right ‘behind’ the Sun.  (This is why our arm of the Milky Way is called the Orion Arm.)  Winter evening skies are much brighter than those of late autumn.

Go Stargazing! September Edition

Venus and Mars have left Saturn behind in the night sky (check out my earlier blog on the position of the planets). You can spot the star Spica in between Mars and Venus during this time of year. (Spica is similar to Mars in brightness and closer to Venus than to Mars). 

 Cloud structure in The Venusian atmosphere,
revealed by ultraviolet observations

September is the last full month to observe Venus at dusk. That’s because Venus has by now come around to Earth’s side of the sun on its faster, inner orbit.  Thus, Venus now begins to overtake the Earth, passing between the Earth and sun on October 29.  We’ll therefore see Venus shift farther to the left of Mars and then drop down below it.  In October, Venus exits the evening sky quite quickly as it shifts back towards the sun.  September and October 2010 is an excellent period for observing Venus’ crescent phase in telescopes.  Anytime Venus is on our side of the sun, more of its night side faces us, resulting in a crescent like appearance when magnified.

Saturn is far to the lower right of Venus and Mars as you face west at dusk.  You’ll need a horizon clear of tall buildings and trees to see it before it sets.  You’ll also need to look early in the month, as Saturn is practically behind the sun by month’s end.  

Jupiter dominates this month’s skies.  On Tuesday morning, September 21, Earth aligns with the sun and Jupiter, bringing Jupiter to opposition (because the sun and Jupiter are then on opposite sides of the Earth).  On the night of September 20-21 we see Jupiter rise at sundown and set at sunup—Jupiter is up literally all night long.  During the whole month, though, Jupiter is visible virtually the whole night.  It outshines all stars in the sky, so it’s easy to find.  Face east in late evening or south southwest at dawn to see it.  The planet Uranus is less than one degree above Jupiter this month; the two planets are closest on September 18.

The Big Dipper is setting in the northwest at dusk; you now need a horizon clear of trees and tall buildings to get a good look at it. You can extend the curve of its handle to ‘arc to Arcturus’, which is in the west at dusk tonight.  Arcturus, by the way, is the fourth brightest star we ever see at night, but the brightest one Americans ever see on a September evening.

As the Dipper gets lower, look for five stars in the shape of an ‘M’ directly across the North Star from the Big Dipper’s handle.  This is Cassiopeia, the Queen—the ‘M’ is the outline of her throne.  Her stars are about as bright as the North Star and the stars of the Big Dipper, so she’s not too hard to find. 

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

High overhead, look for the enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair.   This triangle was up all night long from June to early August, hence its name.  Scorpius, the Scorpion, is in the southwest at dusk.  Sagittarius, the Archer, known for its ‘teapot’ asterism, is to its left.  Between these two star patterns is the center of our Milky Way—the brightest part of that band as wee see it.  On a cloudless night far from the big city, see if you notice the Milky Way glow near the ‘teapot’ of Sagittarius. 

Look for the Great Square of Pegasus rising in the east.  The vast stretch of sky under Pegasus is largely devoid of bright stars—ancients called this the ‘Celestial Sea”. 

Moon Phases in September 2010:

Last Quarter                  September 1, 12:22 am, September 30, 10:52 pm

New Moon                       September 8, 5:29 am

1st Quarter                     September 15, 12:49 am 

Full Moon                        September 23, 4:18 am

At 10:13 pm on Wednesday, September 22, the sun is directly overhead at the equator.  As a result, everyone on earth has the same amount of daylight and the same amount of night.  That’s why it is called the equinox (‘equal night’ in Latin).  In the Northern Hemisphere, we’ve seen the days get a little shorter and the midday Sun a little lower each day since June 21.  For us, the season changes from summer to fall at the equinox.  In the Southern Hemisphere, people have seen the days lengthen and the midday Sun get a little higher each day since June.  For them, the season changes from winter to spring.