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! June Edition

Jupiter
Creative Commons License photo credit: KingArthur10

Sautrn remains well placed in the evening sky this month.  Look for it in the south-southwest at dusk. 

Jupiter, in the south at dawn, is the brightest thing in that part of the sky unless the Moon is nearby (as it is on June 13.) 

Venus is a dazzling morning star this month.  Look east right as day begins to break for the brightest thing there except for the Moon.  Venus remains the ‘morning star’ for the rest of 2009. 

Mars is a little higher in the east at dawn than it has been.  Still, it remains fairly dim.  On the morning of Sunday, June 21, Venus passes within two degrees of Mars.  Look for Mars slightly above Venus and to its left.  This is quite a mismatched pair; Venus is about 100 times brighter than Mars. 

Look high in the west at dusk for stars in the shape of a backwards question mark, with a right triangle to the left of that.  These stars are in Leo, the Lion.  Saturn is under the ‘right angle’ in that right triangle.  The Big Dipper is highest on spring evenings.  From the Big Dipper’s handle, you can “arc to Arcturus.”  Arcturus, in the east at dusk, is the fourth brightest star we ever see at night and will be the brightest star in our night skies during all of June and July. Continuing the curve of the Big Dipper’s handle past Arcturus, you can “speed on to Spica,” a star low in the southeast at dusk.  Spica represents a stalk of wheat held by Virgo, the Virgin, who is in fact the harvest goddess.

Rising in the southeast at dusk is Antares in Scorpius, the Scorpion.  This is a red super-giant star about 700 times as wide across as our Sun.  In the northeast, the Summer Triangle is entering the evening sky.  Vega, the brightest of the triangle’s three stars, is already up at dusk.  The other two stars, Deneb and Altair, are up by 11:00 on June 1.  By month’s end, the whole triangle rises at dusk. 

Moon Phases in June 2009:

Full                                    June 7, 1:11 pm
Last Quarter                  June 15, 5:15 pm
New                                   June 22, 2:35 pm
1st Quarter                     June 29, 6:28 am

Golden Light
Creative Commons License photo credit: Paulo Brandão

At 12:45 am on Sunday, June 21, the Sun is overhead at the Tropic of Cancer and thus is as high as possible in our skies.  This is the summer solstice.  Here in the Northern Hemisphere, we have more daylight on this date than on any other date of the year. 

However, the earliest sunrise occurs on June 11, while the latest sunset is June 30.  Since most of us sleep through sunrise and witness sunset, the days seem to lengthen slightly until the end of the month, when in fact they begin getting shorter after the 21st.  As we approach the summer solstice each year, the Sun appears higher and higher in our skies.  As a result, it takes a longer apparent path across our skies; sunsets occur later and sunrises occur earlier throughout the spring.  But there is very little change in the Sun’s apparent height near the solstice itself.  For example, the Sun is already 82.33333 degrees high at midday in Houston; it will be 83.6666667 degrees high at midday on the solstice.  With such little change in the Sun’s height in June, a different effect dominates—the equation of time.  From June 11-30, both sunrise and sunset get a little later each day. 

Click here for more on the equation of time.