Go Stargazing! March Edition

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

Jupiter leaves the evening sky this month.  For now, you can still observe it in the west at dusk, where it sets by 8:25 on March 1.  It outshines all stars in the sky, so it’s easy to find.  Face west at dusk and look for the brightest thing there.  However, Jupiter is getting a little lower in the sky each evening.  You should be able to follow it until about the middle of the month.  By month’s end, Jupiter is lost in the sun’s glare.  On April 6, it is directly behind the sun from our perspective.

Mercury emerges from behind the sun this month and appears beside Jupiter before Jupiter fades from view.  On March 15, Mercury is about two degrees to the right of Jupiter as they both set in twilight.  As Jupiter becomes lost in the sun’s glare, Mercury remains visible low in the west at dusk for the rest of the month.

Venus remains a dazzling morning star.  It is getting lower in the sky as the angle between the solar system plane and the horizon gets shallower.  Face southeast at dawn, and you can’t miss it.

Saturn is in the southwest at dawn, getting lower in the southwest by month’s end.  This is because at the end of the month, Earth is about to pass between the sun and Saturn.  This alignment, called opposition, puts Saturn in the sky all night long; it rises in the east at dusk and sets in the west at dawn (the precise opposition date is April 3).  As a result, Saturn is also an evening object, rising in the east by 9:00 p.m. on March 1 and by dusk on the 31.

Mars, just past conjunction with the sun, remains lost in the sun’s glare all month.

A swath of brilliant winter stars continues to dominate evening skies.  These stars are now due south at dusk, but shift to the southwest later in the evening.  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.  Leo, the Lion, rises in the east.  The Big Dipper has now fully re-entered the evening sky; it is to the right of the North Star with the handle pointing down.

Below Sirius, just above the southern horizon, is a star second only to Sirius in brightness.  This is Canopus, which marks the keel (bottom) of the legendary ship Argo Navis.  Canopus is so far south, in fact, that most Americans never see it.  From the Gulf Coast, however, Canopus does rise.  March and March are the best months to see it in the evening.

Moon Phases in March 2011:

New Moon                              March 4, 2:46 p.m.

1st Quarter                             March 12, 5:45 p.m.

Full Moon                               March 19, 1:10 p.m.

Last Quarter                          March 26, 7:07 a.m.

At 6:21 p.m. CDT on Sunday, March 20, the sun is overhead at the Earth’s equator, giving everyone in the world the same amount of daylight.  This, then is the vernal equinox, the ‘official’ start of spring.  For us, days have been lengthening since December 21; by now daytime is almost as long as the night.  After March 20, daytime is longer than night for us.  For many people, however, wintry weather continues so long as arctic air masses remain in motion across North America, Europe, and Asia.

Winter time
Creative Commons License photo credit: cvanstane

People in the Southern Hemisphere had their longest days back in December; their days have since shortened to be about equal to the night.  After March 20, night is longer than day down there, so this is their autumnal (fall) equinox.

Sunday, March 13, is the second Sunday in March.  Therefore, Daylight Saving Time begins at 2 that morning (1:59:59 is followed by 3:00:00).  Don’t forget to set your clocks forward one hour on Saturday night, March 12!

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! 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.