Seeing Stars with James Wooten: January 2013

Happy New Year! This January, Mars continues to fade as it drops into the Sun’s glare. It is low in the southwest at dusk.

Jupiter is now up all night long. Opposition, when Earth is directly between Jupiter and the Sun and Jupiter literally rises at sundown and sets at sunup, is Jan. 3. After that date, Jupiter only gets higher and more prominent in the evening sky. Face east/northeast at dusk and look for the brightest thing there (unless the Moon is also there), as Jupiter outshines all stars we see at night.

Venus is lower in the east at dawn than before. You can still observe it this month and next.

Saturn is a little higher in the morning sky this month. Look for it just in the south at dawn.

Sky Map: January 2013

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. Jupiter, outshining all stars in the night sky, is in Taurus between Aldebaran and the Pleiades. In the north, the Big Dipper has been out of sight under the North Star for a while. In January, though, you can look for the two pointer stars, which point at the North Star, peeking over trees and houses to the north/northeast.

Moon Phases in January 2013:
Last Quarter                  January 4, 9:58 p.m.
New                               January 11, 1:44 p.m.
1st Quarter                    January 18, 5:45 p.m.
Full                                January 26, 10:39 p.m.

At 11 p.m. on Tuesday, Jan. 1, the Earth passed as close to the Sun as it will get this year. Thus, Earth is now just past perihelion. If we’re closer to the Sun now, why is it cooler (even in Houston)? Notice how low the midday Sun is right about now. Six months from now, take note of how high the Sun is in June and July. That’s what makes it so much cooler now and so hot then.

The Earth’s orbit is, in fact, almost perfectly circular; there is only a 3-percent difference between perihelion and aphelion distance. The 23.44-degree tilt of the Earth makes the Sun appear high if we tilt towards it and low if we tilt away, and dominates the small effect of Earth’s changing distance.

The latest sunrise of the year (at Houston’s latitude) occurs on Jan. 10. Earth, just past perihelion, has sped up a little in its orbit since it is a little closer to the Sun. As a result, sunrise, local noon, and sunset have been happening a little later each day since early December. The noon Sun is ever so slightly higher at noon each day since the solstice (Dec. 21), but as of today, the Sun is still very close to its solstice height. Beginning Jan. 11, the noon Sun’s greater height in the sky again becomes the dominant effect (as it is for most of the year). From then until June, sunsets are getting later while sunrises are getting earlier.

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. If you’re there, listen for my announcement.

To enjoy the stars in any weather from the comfort of the HMNS Planetarium, click here for a full schedule.

Would you like email updates on current events in the sky, at the planetarium, and at the George Observatory?  If so, send an email to astroinfo@hmns.org.

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.

Go Stargazing! March Edition

Saturn is up all night long by month’s end.  On Mar. 21, Earth passes between the sun and Saturn.  This alignment is called opposition because it puts Saturn and the sun on opposite sides of the Earth.  As a result, Saturn rises at dusk and sets at dawn on this date.  Look for Saturn to rise due east around 8:00 p.m. tonight. It will rise just a little bit earlier each night.

Venus enters the evening sky by the end of March.  As March opens, Venus is still setting during twilight, making it hard to notice at dusk.  By the end of the month, though, Venus has come out from behind the sun far enough for us to notice it clearly.  Face west at dusk and look for a point of light that outshines everything in the sky but the sun and the moon.

Mars has become an evening object.  It is now already up in the east-northeast by dusk.  On Jan. 29, Mars came to opposition as Earth passed between Mars and the sun, putting Mars in our sky all night long.  Earth is now pulling ahead of Mars on its faster orbit.  As a result, Mars is slightly dimmer each night for the rest of 2010.  However, during March, Mars remains brighter than average, and thus remains easy to see.  Look high in the southeast as dusk (due south by the end of the month) for a reddish point of light sort of in line with the two Dog Stars 

Jupiter is mostly out of sight this month.  Viewers with a very clear east-southeast horizon may notice Jupiter low in the sky at dawn by the end of March.  

STEAL ME FOR YOUR DESKTOP!! (The Bokeh Galaxy)
Creative Commons License photo credit: kevindooley

Dazzling Orion is high in the south.  His belt points up 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.  At dusk on 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.  

Meanwhile, spring stars are rising 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 once again fully risen at dusk. Later in the evening, you can extend its handle to ‘arc to Arcturus’ and then ‘speed on to Spica’.  These stars will be along the eastern horizon by 9:30 tonight, and even earlier later in the month.

Transit Lune/Saturne du 22 mai 2007
Creative Commons License photo credit:
ComputerHotline

Moon Phases in March 2010:

Last Quarter                  March 7, 9:43 p.m.

New Moon                      March 15, 4:02 p.m.

First Quarter                  March 23, 5:59 a.m. 

Full Moon                        March 29, 9:25 p.m.

At 12:33 p.m. on Saturday, Mar. 20, the sun is directly overhead at the equator.  This, then, is the vernal equinox. On this date, everyone in the world has the same amount of daylight and the same amount of night.  After this date, daytime is longer than night in the Northern Hemisphere, while night is longer than daytime in the Southern Hemisphere. 

Sunday, Mar. 14, is the second Sunday in March.  Accordingly, we spring forward into Daylight Saving Time at 2 a.m. that morning (1:59:59 a.m. is followed by 3:00:00 a.m.).  Don’t forget to set your clocks forward by one hour before going to bed Saturday night!