Seeing Stars with James Wooten: The Summer Triangle is high in the sky

This star map shows the Houston sky at 10 pm CDT on July 1, 9 pm CDT on July 15, and dusk on July 31.  To use the map, put the direction you are facing at the bottom. The Summer Triangle is high in the east.  This consists of the brightest stars in Cygnus, Lyra, and Aquila.  Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius to his left.  Leo, the Lion, sets in the west.  From the Big Dipper’s handle, ‘arc to Arcturus’ and ‘speed on to Spica’ in the southwest.  Watch Mars close in on Saturn this month.

This star map shows the Houston sky at 10 p.m. CDT on July 1, 9 p.m. CDT on July 15, and dusk on July 31. To use the map, put the direction you are facing at the bottom.
The Summer Triangle is high in the east. This consists of the brightest stars in Cygnus, Lyra, and Aquila. Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius to his left. Leo, the Lion, sets in the west. From the Big Dipper’s handle, ‘arc to Arcturus’ and ‘speed on to Spica’ in the southwest. Watch Mars close in on Saturn this month.

This month, Mars is in the southwest at dusk this month. Mars continues to fade a little each night as Earth continues to leave it farther behind. Still, Mars rivals the brightest stars we see at night.

Saturn is also in the southwest at dusk. This month and next, Mars approaches Saturn more and more. 

Venus remains in the morning sky. Look east at dawn for the brightest point of light there; only the Sun and Moon outshine Venus. Venus remains a morning star for almost all of 2014.

Jupiter is behind the Sun and out of sight this month. 

The Big Dipper is left of 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 west at dusk. Leo, the Lion, is setting in the west at dusk.

Antares, the brightest star of Scorpius, the Scorpion, is in the southeast, with the ‘teapot’ of Sagittarius rising behind it. The Summer Triangle has fully risen in the northeast. The stars of summer are here.  

Moon Phases in July 2014:

1st Quarter: July 5, 7:00 a.m. 
Full: July 12, 6:26 a.m.
Last Quarter: July 18, 9:09 p.m.
New: July 26, 5:42 p.m.

At about 7 p.m. on Thursday, July 3, Earth is as far from the Sun as it will get this year. This is aphelion, when Earth is 94.56 million miles from the Sun, as opposed to the average distance of 93 million miles. On January 4, Earth was at 91.44 million miles from the Sun; that was perihelion (closest approach to the Sun). It turns out that this variation in the Earth-Sun distance is too small to cause much seasonal change. The tilt of Earth’s axis dominates as it orbits the Sun. That’s why we swelter when farther from the Sun and shiver when we’re closer. 

Click here to see what’s happening this month in the Burke Baker Planetarium

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. 

Clear skies!

Seeing Stars with James Wooten: July 2013

Venus remains in the west at dusk. It outshines everything but the Sun and Moon, so you can begin observing it during deep twilight.

Saturn is now shining in the south/southwest at dusk. Although not as bright as Venus, it does outshine the stars around it, so you can’t miss it.

Mars and Jupiter emerge into the morning sky this month. Look for them low in the east/northeast at dawn, with Jupiter much brighter. Mars passes less than one degree from Jupiter on the morning of July 22.

Sky Map July 2013

The Big Dipper is above the North Star and to its left, with its handle pointing up. From that handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars are in the south 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 to its left. The Summer Triangle is high in the east. The stars of summer are here.

Moon Phases in July 2013:

New                               July 8, 2:15 a.m.
First Quarter                 July 15, 10:19 p.m.
Full                                July 22, 1:15 p.m.
Last Quarter                 July 29, 12:44 p.m.

At about 10 a.m. on Friday, July 5, the Earth is as far from the Sun as it will get this year — a position known as aphelion. It may seem counterintuitive to be farthest from the Sun now and closest to the Sun just after the New Year, however, the Earth’s orbit is almost a circle; the difference between perihelion and aphelion is too small to affect our seasons.

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. I generally do one such tour on short May nights.

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

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.

See Comet Hartley 2!

Perhaps you were able to observe Comet McNaught this past June and July.  In case you missed that comet, however, another brighter than average comet has approached the Earth this October. Comet Hartley 2 is now visible in binoculars, and could be a naked-eye object around the time of its closest approach to Earth on October 20. As its name indicates, this is the second comet found by Malcolm Hartley. He discovered this comet in 1986 at the Siding Spring Observatory in Australia. Comet Hartley 2 is a small object only about 1.5km across. It orbits the sun once in about 6.5 years, attaining a maximum (aphelion) distance from the sun of about 5.87 AU (beyond Jupiter’s orbit) and a minimum (perihelion) distance of about 1.05 AU (just beyond Earth’s orbit). This orbit places it in the Jupiter family of comets, which orbit in the same direction as the planets with periods of less than 20 years.   In fact, there is evidence that interaction with Jupiter has shortened Hartley 2′s orbital period from over 9 years to the present 6.5.

In October 2010, Hartley 2 comes to perihelion while Earth is on the same side of the sun. This brings Hartley 2 within 11.2 million km of the Earth, close enough to make it visible in our skies—possibly even to the naked eye.  Many comets come inside the Earth’s orbit as they approach the sun, which means we look more or less in the sun’s direction when seeing them at their brightest.  Hartley 2, on the other hand, has a perihelion just outside Earth’s orbit, so Earth is passing roughly between the sun and the comet this month.  Therefore, we can observe it while looking away from the sun in our sky. 

 Halley’s Comet with tail

Comets are made of ice and dust and are often called ‘dirty snowballs.’  We believe they are left over from the formation of the solar system.  As comets approach the sun, ice changes into gas and dust embedded in the ice is released.  A cloud of particles expands out to form a coma around the comet’s solid nucleus. This coma may be a hundred thousand miles across. Radiation pressure of sunlight and the powerful solar wind sweep gases and dust away from the comet’s head, forming tails pointed away from the sun.  Comets have bluish gas tails and yellowish dust tails.   Since Earth is passing more or less between the sun and Hartley 2, however, its tails will be mostly oriented away from us and foreshortened from our point of view. 

Hartley 2′s coma is now quite large in our sky, so you should look for a fuzzy area, perhaps bigger than the full moon, not a single point of light. The total brightness of the comet is about that of the dimmest stars visible, so the farther you can get from city lights, the better.  The large coma means that Hartley 2′s brightness is diffused over a large area, and therefore the comet may look dimmer than its total brightness would suggest.  Averted vision, which involves looking slightly away from the comet’s actual position, may help you see Hartley 2 if it is at the threshold of visibility.   If you choose a viewing site far from big cities and a night with no moon, you may see the comet with the unaided eye.  The extended coma has a soft, diffuse look comparable to the Milky Way band.  

October 20, the day of closest approach to Earth, has a large waning gibbous moon approaching its full phase on October 22.  Before the full moon, it may be easier to spot Hartley 2 at dawn, after the moon has set.  Or, you can look towards the end of the month, with the moon is at Last Quarter.   Here  is a chart showing Hartley 2′s position through November 3, 2010.  (Note that the dates given are in Universal Time, which corresponds to the previous evening for us.)  Of the constellations shown, Perseus rises in the northeast at dusk in mid-October, while Auriga comes up at about 9:30, also in the northeast.  Gemini, the Twins, rises closer to midnight. Keep in mind that predictions for a comet’s brightness are just that–predictions.  many comets appear significantly brighter or dimmer than expected. 

 Tempel 1 as photographed by Deep Impact

Amateur astronomers who get out and observe this comet won’t be alone in observing Hartley 2.  NASA has retargeted its Deep Impact spacecraft to fly past Hartley 2 on November 4, 2010.  Back in 2005, NASA used Deep Impact to study comet Tempel 1.  In that mission, scientists released a probe to impact Tempel 1 and study the material released.  Deep Impact will simply fly by Hartley 2, however, taking advantage of this opportunity to study yet another comet up close.

With its short orbital period, Hartley 2 should return for its next perihelion near April 20, 2017.  Earth, however, will not be on the same side of the sun as Hartley 2 in 2017, so the comet will be much dimmer in our sky.  Hopefully, our skies will cooperate, and Hartley 2 will brighten as expected or even more, and we’ll all get to appreciate a fascinating sight in the fall 2010 sky.