Go Stargazing! December Edition

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

Mercury has emerged into the evening sky, and is visible at the beginning of this month.  Look low in the southwest at dusk, right over the point of sunset.  By mid-month, Mercury is again lost in the Sun’s glare; it re-aligns with the sun (is at inferior conjunction) on Dec. 19.

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

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

mars-06-crop
Creative Commons License photo credit: chipdatajeffb

Mars is now 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.

Look for the enormous Summer Triangle in the night sky, consisting of the stars Deneb, Vega, and Altair, in the west.  These stars were up all night long back in June and July, hence the name. The Great Square of Pegasus, not quite as bright as the Summer Triangle, is high in the south at dusk.  The star in its upper left hand corner is also the head of Andromeda.  Rising after Andromeda is Perseus, the hero that saved her life.  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.  Taurus, the Bull rises in the northeast.  Look for the Pleiades star cluster at the feet of Perseus.  Dazzling Orion, the Hunter rises shortly after dusk (by month’s end, it is already up at dusk).  As Orion enters the evening sky, we transition from the relatively dim evening skies of autumn to the brilliant stars of winter.

Moon Phases in December 2010:

New Moon                             December 5, 11:36 a.m.

1st Quarter                            December 13, 7:58 a.m.

Full Moon                              December 21, 2:14 a.m.

Last Quarter                         December 27, 10:19 p.m.

Eclipse burning bright
Creative Commons License photo credit: ericskiff

The full moon of early Tuesday, December 21, enters the Earth’s shadow, causing a total lunar eclipse.  This eclipse is visible in its entirety from all of North America, including Houston.  The moon first encounters the Earth’s shadow (umbra) at 12:32 a.m.  This marks the beginning of the partial eclipse.  The moon takes just over an hour, until 1:40 a.m., to enter the shadow.  That is when totality begins.  In this eclipse, the Moon does not quite cross the center of Earth’s shadow but instead passes through the northern part of it.  Even so, the moon takes 74 minutes to cross to the other side of the shadow, so totality lasts from 1:40 to 2:54 a.m.  By 4:02 a.m., the moon has re-emerged from the shadow, and the eclipse is over.  Remember, seeing a lunar eclipse requires no special equipment at all; anyone who sees the moon sees the eclipse.  The only thing that could stop us from seeing this would be a cloudy night on December 20-21, 2010.  The next total lunar eclipse we see here in Houston occurs just after midnight on April 15, 2014.

At 5:42 p.m. on Tuesday, December 21, the sun is overhead at the Tropic of Capricorn, the most southerly latitude where the sun can be overhead.  This is therefore the winter solstice for those of us in the Northern Hemisphere, and the summer solstice for people south of the equator.

At Houston’s latitude, the earliest sunset of the year occurs Thursday, December 2.  Of course, days continue to shorten until the solstice, which makes sunset earlier and sunrise later.  However, Earth is also accelerating as it approaches perihelion (closest approach to the sun) in early January.  This causes sunrise, local noon, and sunset to occur slightly later each day.  This close to the solstice, the second effect actually predominates, so sunset gets a little later during December even while the days are getting shorter.  As you head out to ring in the New Year, notice that sunset on New Year’s Eve is about 10 minutes later than it is now.

2009 Leonid Meteor (cropped, afterglow closeup)
Creative Commons License photo credit: Navicore

The Geminid meteor shower peaks every year in mid-December, this year on the 14.  This shower and the Perseids in August are the two most reliable showers of the year, producing about 1 or two meteors per minute.  The Geminids are not as popular, though, because of colder nights (yes, sometimes even in Houston) and a greater chance of cloudy skies.  Still, it’s worth a look if the skies are clear.  Unlike most meteor showers which are comet debris, the Geminids originate from an asteroid (3200 Phaethon.  The shallower angle between this debris path and Earth’s orbit means that Earth rotates us towards the debris field before midnight.  We can thus observe meteors from late evening all the way until dawn.  Meteors will seem to radiate from the constellation Gemini, hence the shower’s name.

Go Stargazing! November Edition

The king of planets, Jupiter, which dominted the evening skies of September and October, is still well placed for obeserving in the evening during this month. It outshines all stars in the sky, so it’s easy to find. Face southeast at dusk.

Hubble Images Suggest Rogue Asteroid Smacked Jupiter
Creative Commons License photo credit:
NASA Goddard Photo and Video

Mars remains very low in the southwest at dusk; it is of only average brightness and hard to recognize.  It will be even harder to see in the months to come, as Earth passes around the far side of the sun from it.

Venus passed between the Earth and the sun on Oct. 29, an alignment known as inferior conjunction.  In other words, Venus has just ‘lapped’ us on its faster, inner orbit.  As a result, in November 2010 we see Venus emerge quickly into the morning sky.  Face southeast at dawn, especially beginning around mid-month, and you can’t miss it.  If you are a consistent early riser, you can do an experiment.  Observe the southeast horizon before dawn (5:30-5:40 a.m. once we fall back) and see for yourself when you can first see Venus.

Saturn is in the southeast at dawn, above the much brighter Venus.  Look for the ringed planet low in the east at dawn.

Look for the enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair, in the west.  These stars were up all night long back in June and July, hence the name. The Great Square of Pegasus, not quite as bright as the Summer Triangle, is high in the east at dusk.  The star in its upper left hand corner is also the head of Andromeda.  Rising after Andromeda is Perseus, the hero that saved her life.  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. The vast stretch of sky under Pegasus is largely devoid of bright stars—ancients called this the ‘Celestial Sea.”  The only first magnitude star in the entire region is Fomalhaut, in the Southern Fish.  Jupiter’s stark brilliance is even more remarkable against this dim backdrop.  Taurus, the Bull rises in the northeast.  Look for the Pleiades star cluster at the feet of Perseus, low in the northeast just after dusk.

Moon Phases in November 2010:

New Moon                      November 5, 11:51 p.m.

1st Quarter                     November 13, 10:39 p.m.

Full Moon                       November 21, 11:27 a.m.

Last Quarter                  November 28, 2:36 a.m.

Sunday, Nov. 7 is the first Sunday of the month.  Accordingly, we fall back from Daylight Saving Time to Standard Time on that date.  Don’t forget to set all your clocks back on Saturday, Nov. 6 before going to bed.  Enjoy your extra hour of sleep!


*Time* Ticking away...
Creative Commons License photo credit: Michel Filion

Catch a Falling Star!

Our guest blogger today is Barbara Wilson. She is an astronomer at the museum’s satellite facility, The George Observatory. Today she is writing about the Perseid Meteor Shower, which can best be seen the night of August 11 through the dawn of August 12.

Looking at the summer meteor showers are an all time favorite hobby of mine.  For the past few years I have always planned on being somewhere away from the city lights so I can fully enjoy the “Night of Falling Stars” in August.  Some years the meteors are sparse, but sometimes there are so many that you can’t possibly see them all. Part of the fun is just not knowing what to expect.  But I think that this will be the best meteor shower of 2008.  On the morning of August 12, just before dawn on Tuesday is when we should see the most meteors.

The George Observatory, a satellite facility of the Houston Museum of Natural Science located in Brazos Bend State Park, will host an all-night viewing of the annual Perseid meteor shower on the observing deck from 9 p.m. on Monday evening, Aug. 11 through dawn on Tuesday, Aug 12.

Here are some common questions about the shower.

What time will we see the falling stars?

0170935-R1-007-2_001
Creative Commons License photo credit: twinxamot

The meteors (also known as “falling stars”) should become visible as early as 10 p.m. Monday evening, Aug. 11.  We should see many more per hour after midnight when the “radiant” gets higher by each passing hour.  The moon will set around 2 a.m., leaving a darker sky for meteors, and I hope we will see as many as 60 to 90 meteors per hour between 2 a.m.  and dawn on Tuesday. The peak of the shower is estimated to happen close to dawn for us here in Houston.

Where do I look?

A quick answer: the northeastern sky. 

Perseus With the Head of Medusa
Creative Commons License photo credit: storem

Meteor showers are named for the constellation where the meteors appear to be falling from.  This spot in the sky is called the “radiant” by astronomers. So the Perseids appear to come from the constellation “Perseus the King,” hence the name.

Perseus rises in the northeastern sky. But you will notice meteors all over the sky, not just in the north.  In fact, if you face south, west, or look overhead, you will see the longest meteors.  The closer you look to the radiant the shorter the meteors are. It is a perspective effect.

Where should I be to see the most meteors?

Quick answer: Away from the city.
Many more meteors are seen when you travel away from city lights.  Bright lights affect the amount of meteors seen.  A few of the meteors are very bright and visible, even in big cities, but most are not.

Meteors are bits of dust and debris left in space by comets that have passed through our solar system. Here’s a bit of science on meteors from Dr. Phil Plait’s book, “A meteoroid, moving at 33,500 mph (15 kilometers a second) or more compresses the air in front of it violently. The air itself gets very hot, which is what heats the meteoroid, as a result we see the light from the meteor.” Despite the heated air and bright streaks, the meteor light is still much dimmer than the lights of the city around us.

As a result only the very brightest meteors can be seen from cities. So we invite people to join us at the George Observatory as the skies are many times darker than in Houston or surrounding cities.
 
What should I bring to be comfortable?

Star Gazing in Toronto
Creative Commons License photo credit: wwfcanada

It should be loads of fun, so bring your lawn chairs, blankets to lie on, mosquito repellant, a late night snack, and hope for clear skies!  You can bring a red filtered flashlight, but please do not bring bright white flashlights, as the bulbs are just too bright and will interfere with seeing the meteors. Binoculars are not necessary, your eyes are all you really need.

The state park will charge a $5.00 per person entry fee, with children under 12 free of charge.

Please note: There was a date misprint in Museum News, (Vol 13, # 4 Ice Worlds) the George Observatory will not be open on the night of August 12/13th.