Go Stargazing! August Edition

This month the great planet race continues, as Venus, Mars and Saturn form a triangle in the west.  Watch the triangle change shape each night as Venus overtakes Saturn and then Mars!

Venus is by far the brightest of the three planets.  Face west at dusk and look for a point of light that outshines everything in the night sky.

Saturn and Mars are to the upper left of Venus as August opens.  Mars is below Saturn and a bit to its left.  Although these two planets of similar brightness are much dimmer than Venus, they outshine all the other stars near them.

Observe all three carefully throughout August and watch as their configuration changes.  Mars aligned with Saturn last Saturday (July 31) and now begins to move farther to Saturn’s left.  Venus, moving faster than the other two, continues to approach from the right; it will pass Saturn on August 8.  Venus then continues to gain on Mars as they both move away from Saturn.  Venus finally overtakes Mars on August 19-20.  On the night of August 31, Venus and Mars are to either side of the star Spica in Virgo.

Jupiter is now a late evening object, rising by 11 p.m now and by 8:45 p.m. at month’s end.  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 Big Dipper is in the northwest at dusk. You can extend the curve of its handle to ‘arc to Arcturus’ and then ‘speed on to Spica’.  These stars are 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 an August evening.  Spica is in Virgo, the constellation where this month’s ‘planet race’ occurs.

In the east, look for the enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair.   This triangle is up all night long from June to early August, hence its name.  Scorpius, the Scorpion, is in the south 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.  In late evening, look for the Great Square of Pegasus rising in the east.

Moon Phases in August 2010:

Last Quarter                        August 3, 12:00 a.m.

New Moon                              August 9, 10:08 p.m.

1st Quarter                           August 16, 1:14 p.m.

Full Moon                              August 24, 12:05 p.m.

Perseid Meteor 8/12/08
Creative Commons License photo credit: aresauburn™

On Friday morning, August 13, the Earth passes through a stream of debris left long ago by Comet Swift-Tuttle.  This produces the Perseid Meteor Shower, one of the best meteor showers each year.   The Perseids occur every year at about this time, producing on average about one meteor per minute.  Keep in mind that even a short period such as a minute can seem longer if you are waiting for something to happen.  Since Earth is running into the meteors, not the other way around, the leading edge of the Earth encounters the shower.  This is the side going from night into day.  Accordingly, we see more meteors as dawn approaches.  Big city lights or the Moon can limit the meteors you see by dimming out fainter ones.  This August, however, the New Moon is on the 10th, giving us a skinny crescent on the 12th which sets long before the shower really gets going.  The main challenge, then, is to avoid city lights.

If skies that night are clear, our George Observatory will open Thursday night, August 12 at 9pm and remain open until dawn for observing the shower.  If you come out to George or go elsewhere, you’ll want to lie on your back (to see as much of the sky as at once as possible) and orient yourself towards the constellation Perseus.  (The shower is called the ‘Perseids’ because they seem to radiate from that constellation.)  Perseus rises in the northeast at dusk and is high in the north at dawn.

Go Stargazing! July Edition

During July, you can watch a great planet race, as Venus closes in on Mars while they both close in on Saturn!

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.

Venus remains high in the evening sky during July.  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 also in the western sky.  Look in the west at dusk for a reddish point of light between Venus and Saturn.

Observe all three carefully throughout July and watch as they get closer together.  By July 31, Mars will have caught up to Saturn, with Venus only about 7.5 degrees away.  Keep watching next month as Mars moves ahead of Saturn and Venus passes them both.

Jupiter is in the south at dawn this month.  It outshines all stars in the sky, so it’s easy to find.  By July 31, Jupiter rises at about 11 p.m.; it will be a late evening object next month.

In the 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.  This month, the Lion serves as the backdrop for the great planet race described above.  The Big Dipper is high in the northwest 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 west and southwest, 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 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 July, hence its name.  Scorpius, the Scorpion, is in the southeast 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.

Summer Triangle

Moon Phases in July 2010:

Last Quarter                       July 4, 9:36 am

New Moon                            July 11, 2:40 pm

1st Quarter                         July 18, 5:11 am

Full Moon                            July 25, 8:36 pm

Flag of Turkey
Creative Commons License photo credit: steelight

The new moon of Sunday, July 11, will align precisely with the sun and Earth, casting its shadow on the Earth.  This will cause a total solar eclipse.

Unfortunately, the shadow’s path is entirely over the South Pacific Ocean.  Easter Island and certain islands of French Polynesia are the only land where totality can be seen.  Even partial phases are visible only from South America.

On Tuesday, July 6, Earth is as far from the sun as it will get this year, a position called aphelion.  Remember, the Earth’s orbit is not quite a circle but an ellipse.  We are therefore slightly closer to the Sun in January than in July.  Also, remember that the difference between our January and July distances from the Sun is small.  When it comes to making us hotter or colder, the effect of our axial tilt dominates.

Go Stargazing! May Edition

Saturn
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! April Edition

Saturn, up all night long last month, can now be found in the east southeast at dusk.  We are seeing its rings a little more edge on than earlier in the year, an effect that gets even more pronounced next month.

Venus keeps getting higher in the evening sky during the month of April.  Face west at dusk and look for a point of light that outshines everything in the sky. As April opens, Venus has a companion; the elusive Mercury is to its lower right.  Normally too close to the sun to appear in our night sky, Mercury has come from behind the sun and appears far enough to its side that we can still see it just after sunset. Mercury’s greatest elongation (apparent distance from the sun) occurs on April 8.  After that date, we see Mercury return towards the sun’s glare.

Mars is very high in the evening sky, although not as bright as it was in winter.  Since Jan. 29, the 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 April, Mars remains brighter than average and thus remains easy to see.  Look high in the south 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.

Johannes Hevelius drew the Orion constellation
in Uranographia, his celestial catalogue in 1690

Now that the winter is over, the winter stars have shifted to the west.  Dazzling Orion is high in the southwest.  His belt points right to Aldebaran, the eye of Taurus, the Bull.  The Dog Stars Sirius and Procyon are to Orion’s left.  Sirius is the brightest star we ever see at night.  Gemini, the Twins, are to Orion’s upper left.  Look for two stars of equal brightness less than 5 degrees (three fingers at arms’ length) apart.  These are Castor and Pollux, marking the twins’ heads.  High in the northwest is Capella, the sixth brightest star ever seen at night.

Meanwhile, the spring stars are high in the 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 high in the northeast at dusk. If you have a clear eastern horizon, you can extend the curve of its handle to ‘arc to Arcturus’ and then ‘speed on to Spica.’  These stars are along the eastern horizon by dusk tonight.

Star Cloud Over Saskatchewan.jpg
Creative Commons License photo credit: Space Ritual

The large contrast between the bright winter stars in the west at nightfall and the dimmer spring stars in the east arises because of the shape of our Milky Way. The Galaxy is a barred spiral much thinner than it is wide across. Thus, most stars are near the plane of the galaxy.  Orion, Taurus, Gemini, and the Dogs are near the galactic plane, while Arcturus and the stars of Leo and Virgo are far above it.



Moon Phases in April 2010:

Last Quarter                  April 6, 4:37 a.m.

New Moon                      April 14, 7:30 a.m.

1st Quarter                     April 21, 1:19 p.m.

Full Moon                       April 28, 7:18 p.m.