Go Stargazing! July Edition

Saturn is the only planet visible to the naked eye in the evening skies of July, 2011.  Face south-southwest at dusk, and you’ll see Saturn near a star of similar brightness—Spica in Virgo.  Saturn is a bit to the right of Spica as you face southwest.   The ringed planet remains well placed for evening viewing, and remains in the evening sky until late September 2011.

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

Mars and Jupiter are now higher in the pre-dawn sky.  Jupiter, set against a background of very dim stars, dominates the eastern sky at dawn.  Mars is dimmer and much lower in the east northeast.  It has fully emerged from the sun’s glare, and will brighten slightly each morning.  Venus is now out of sight, as it is passing around the far side of the sun from our perspective.

The Big Dipper is above the North Star, with its handle pointing up.  From that handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars are in the southwest at dusk.  Leo, the Lion, sets in the west at dusk.

Antares, brightest star of Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius rising behind it.  The Summer Triangle has fully risen in the northeast.  The stars of summer now dominate the evening sky.

Moon Phases in July 2011:

New Moon                       July 1, 4:02 p.m.

1st Quarter                     July 8, 9:09 p.m.

Full Moon                        July 15, 3:12 p.m.

Last Quarter                  July 23, 6:48 a.m.

Winter Solstice Lunar Eclipse
Creative Commons License photo credit: Bruce McKay~YSP

The new moon of July 1 partially blocks the sun, but only as seen from the Antarctic.  No one will get to see a total eclipse because the moon’s full shadow, or umbra, passes just below the Earth.

As we celebrate our independence this July 4, Earth will be at aphelion (at its greatest distance from the sun).  The precise time is 10 a.m.  Perihelion, the Earth’s closest approach to the sun, occurs in January.  Earth has perihelion and aphelion because its orbit is not a circle but an ellipse with an eccentricity (out-of-roundness) of about 1.6%.  Such a small variation, however, exerts no significant influence on our seasons, as you can determine for yourself by stepping outside.  The 23.5 degree tilt of Earth’s axis, on the other hand, is a much more dominant effect.  The very high midday sun of July ensures long days and baking heat in Houston and across much of the Northern Hemisphere.

By popular demand, our George Observatory will open to the public Fridays and Saturdays this summer (except July 8, due to a prior booking).  The Discovery Dome, our traveling planetarium, will be set up each of these Fridays to show films throughout the evening.

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! January Edition

The full moon of Jan. 15 partially blocks the sun, causing an eclipse visible in Africa and Asia. Because it is close to apogee, the moon is too small in the sky to ever block the sun completely, and no total eclipse occurs. Instead, folks on a path stretching from Uganda and Kenya across the Indian Ocean to Sri Lanka, Burma, and China see an annular eclipse. The moon will appear to be completely inside the sun’s disk with a ring of sun around it.

Eclipsed? Not totally.
Creative Commons License photo credit: James Jordan

At about 6 p.m. on Saturday, Jan. 2, the Earth came to perihelion. This means it was as close to the sun as possible—about 147 million km away (Earth is about 152 million km from the sun in July). This is not enough of a difference to influence our weather. Earth’s 23.5 degree tilt is much more important. Our North Pole is still tilted very much away from the sun and the sun still takes a very low path across our sky. Therefore, in spite of being as close to the sun as we’ll be all year, we’re going to be quite cold in Houston this week.

The latest sunrise of the year (at Houston’s latitude) occurs on Jan. 10. Earth is now just past perihelion, and 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 on 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.

Jupiter is the brightest thing in the evening sky this month, except for the moon. You can easily see it by looking to the southwest.  Jupiter appears lower and lower to the horizon each January night.  By the end of the month, Jupiter sets just after 7 p.m.  At the end of February, Earth and Jupiter will be on opposite sides of the sun and Jupiter will therefore be invisible to us.

Mars has become an evening object.  It now rises in the east about 8 p.m. and will rise by dusk at the end of the month.  Mars already outshines all stars in the night sky except the very brightest (Sirius), and will continue to brighten throughout January.  On Jan. 29, Earth will pass between Mars and the sun, putting Mars in our sky all night long (this alignment is called opposition).

Saturn
Creative Commons License photo credit: Elsie esq.

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

Venus is behind the sun (at superior conjunction) on Jan. 11 and is therefore not visible this month.

The Great Square of Pegasus is in the west at dusk.  The star in its upper left hand corner is also the head of Andromeda.  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.  Since the Dipper is low and out of sight at dusk this month, Cassiopeia rides high.

Dazzling Orion is high in the southeast, 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.

Moon Phases in January 2010:

Last quarter moon                 January 7, 4:41 am
New moon                                January 15, 1:12 am
First quarter moon                January 23, 4:53 am 
Full moon                                 January 30, 12:18 am

Go Stargazing! December Edition

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

Jupiter is the brightest thing in the evening sky this month, except for the moon. Face southwest and look for the brightest point of light there. Mercury makes one of its rare appearances this month. Look southwest at dusk right over the point of sunset to see it. Mars is now high in the west at dawn. It is also brightening as the Earth approaches it. Earth and Mars will align late next month, putting Mars in our sky all night long. Saturn is now high in the east at dawn. Venus is beginning to pass on the far side of the Sun from our perspective. It is now so close to the Sun in our sky that it doesn’t rise until after dawn. Look very low in the southeast in morning twilight to see it.

The enormous Summer Triangle, consisting of the stars Deneb, Vega and Altair, sets in the west. The Great Square of Pegasus is overhead at dusk. The star in its upper left hand corner is also the head of Andromeda. Facing north you’ll see five stars in a distinct ‘M’ like shape—that is Cassiopeia, the Queen. Her stars are about as bright as those in the Big Dipper; she is directly across the North Star from the Dipper. Since the Dipper is low and out of sight at dusk this month, Cassiopeia rides high in the sky.

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 rise in the early evening, they rise earlier and earlier as the month goes on, and will appear in the sky below Orion in the east. Sirius is the brightest star we ever see at night.

Moon Phases in December 2009

Full moon                 Dec. 2, 1:31 a.m.
Dec. 31, 1:13 p.m.

Last quarter             Dec. 8, 6:15 p.m.

New moon                 Dec. 16, 6:02 a.m.

1st quarter              Dec. 24, 11:35 a.m.

The new moon of Dec. 16 happens to mark the Islamic New Year. 1 Muharram 1431 A.H. actually begins a few days later, when the crescent moon is first seen just after sunset.

At 11:47 a.m. on Monday, Dec. 21, the Earth’s North Pole is tilted away from the sun as much as possible, making the sun as low in our sky as possible. This is the winter solstice, with less daylight for us than any other day of the year. Although December 21 is the shortest day, it does not have the earliest sunset. At Houston’s latitude, that occurred yesterday (December 2).

Orbit
Creative Commons License photo credit: Shutr

Earth is now about a month away from its closest approach to the sun (perihelion). As it comes slightly closer to the sun, it speeds up a little. This causes sunrise, local noon, and sunset to happen a little later each day. The noon sun won’t get much lower than it is now; we are already that close to the solstice. During December, the effect of Earth speeding up dominates. In the next few weeks, sunsets will occur a little later and sunrises a few minutes later each day. Since most of us sleep through sunrise and see sunset, days will seem to lengthen between now and the solstice, when they’re really getting a little shorter.

If December 21 is sunny, come join us on our museum sundial at noon for solar observing! If not, you can still observe the sun on our sundial near noon any clear day in December or even early January. The holes on our gnomon aligned with the winter solstice are exceptionally large to allow for the cloudier winter weather.