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.

Go Stargazing! February Edition

Jupiter!
Creative Commons License photo credit: Joshua Bury

Jupiter leaves the evening sky this month.  You can still see it during the next two weeks if you face southwest at dusk and look for the brightest point of light there. Jupiter sets by 7:30 as February opens, so you must look soon after dusk to see it.   However, Jupiter sets earlier and earlier and appears lower and lower to the horizon each February night, and soon disappears into the sun’s glare.  On Tuesday, Feb. 16, observers with a clear view of the horizon during twilight can try to see a very close conjunction of Jupiter and Venus, which is slowly moving out of the sun’s glare.  By the end of the month, Earth and Jupiter are on opposite sides of the Sun and Jupiter is therefore invisible to us.

Mars has become an evening object.  It is now already up in the east-northeast by dusk.  Mars already outshines all stars in the night sky except the very brightest (Sirius), and will continue to brighten throughout February.  On Jan. 29, Mars came to opposition as Earth passed between Mars and the sun, putting Mars in our sky all night long.  Earth now starts to pull ahead of Mars on its faster orbit.  As a result, Mars is slightly dimmer each night for the rest of 2010.  However, during February, Mars remains about as bright as the brightest stars, and thus remains easy to see.

Saturn is now high in the southwest at dawn.  Although not as bright as Mars this month, Saturn is brightening as it approaches its own opposition in March.

Joseph Nollekens (1737 - 1823) Castor and Pollux front (V&A 2007)
Castor and Pollux
Creative Commons License photo credit: ketrin1407

Dazzling Orion is high in the south, reminding us that winter is here.  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.  Gemini, the Twins, are to Orion’s left as he rises (and to his upper left once they appear to the south).  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 northeast is Capella, the sixth brightest star ever seen at night.  On February and March evenings, look below Sirius and a bit to its right for Canopus, the second brightest star we ever see at night. This star is in the keel (bottom) of the legendary ship Argo.  Canopus is so far south that most Americans never get to see it.  We, however, are far enough to the south that it barely rises for us, remaining low on the southern horizon.

Moon Phases in February 2010:

Last Quarter                  February 5, 5:50 pm
New Moon                      February 13, 8:52 pm
1st Quarter                     February 21, 6:42 pm 
Full Moon                       February 28, 10:37 am

The new moon of Feb. 13 is the second new moon after the winter solstice.  Accordingly, it marks the Chinese New Year, beginning the Year of the Tiger.  (Correct for the time zone difference, and you’ll see that the date is February 14 in China).

Chinese New Year - Dragon
Creative Commons License photo credit: ajagendorf25

Go Stargazing! February Edition

Venus continues to dominate the western sky on February evenings.  Look west-southwest right as night falls for the brightest thing there except for the Moon, which is nearby at the end of the month.  Venus, on its faster orbit, is coming around to our side of the Sun (and will pass us in March).  Therefore Venus is about as bright as it can be this month. 

Saturn is now a late evening object, rising in the east by 9 p.m. now and by 7 p.m. at month’s end.  Early next month, it will be opposite the Sun in the sky and be visible all night long. 

Mars and Jupiter are lost in the Sun’s glare much of this month.  They form a close conjunction on the morning of February 17, but the pair rises right as the twilight begins to brighten the sky that morning.  Mercury joins them later in the month. 

Dazzling Orion rises in the east, reminding us that winter is here.  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
Creative Commons License photo credit: Fingerz


Moon Phases in February 2009:

1st Quarter             February 2, 5:12 pm
Full Moon               February 9, 8:49 pm
Last Quarter           February 16, 3:38 pm
New Moon             February 24, 7:35 pm

The Full Moon of February 9 almost enters the Earth’s shadow.  It does enter a region of space called the penumbra, in which the Earth partially blocks the Sun.  This event is thus called a penumbral eclipse.  However, it begins right as the Moon is about to set here in Houston.  What’s more, a penumbral eclipse is only a slight darkening of the Moon, barely noticeable in the darkest skies.  In the morning twilight of February 9, you won’t see much of any difference in the Moon as it sets.

IMG_0959
Creative Commons License photo credit: S1lvers Family


Punxsutawney Phil saw his shadow on Groundhog Day, meaning six more weeks of winter.  What does this have to do with astronomy?  Well, Groundhog Day occurs about halfway between the winter solstice and the vernal (spring) equinox.  It therefore occurs near one of the cross-quarter days, called Imbolc by the Celts.  The other three are at the beginning of May, August, and November, and they represent points halfway between the quarter days, which are the equinoxes and solstices. 

Since we don’t want Phil to see his shadow, we clearly don’t want sunshine on February 2.  If this seems ‘backwards,’ consider that there is another day when we don’t want sunshine or warmth-Christmas. 

Houstonians still fondly recall our Christmas Eve snowstorm of 2004, while a similar snowfall on January 24 would have been much less romantic.  The French have the saying, “Christmas on the balcony, Easter by the fireplace.”  Early pagans considered the winter solstice and Imbolc symbols of winter itself.  If these days were appropriately wintry, with clouds and cold, then it was a sign that all was in order.  Winter, which was happening on time, would end on time.  However, if these days were not appropriately wintry, then something was wrong, and a ‘remedial’ winter would need to occur in springtime.  The traditions of the winter solstice and Imbolc were transferred to Christmas and Groundhog Day, respectively.  Thus, sunny weather (with shadows) is a bad omen on Groundhog Day, while cloudy weather (no shadows) is a good omen. 

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.