It’s The Final Countdown or Cassini Spacecraft’s Grand Finale

   Two months from this posting, September 15th, the Cassini spacecraft will end its mission at the planet Saturn by diving into the planet’s atmosphere and self destruction.
   This animated graphic shows the hourly position of the Cassini spacecraft as it makes a distant flyby of two of Saturn’s smaller moons, Atlas and Janus on July 19th. (the moons and spacecraft have been greatly enlarged to make them visible)
20 Years Ago
   On October 14, 1997, NASA launched Cassini, its largest interplanetary spacecraft, on a nearly seven-year voyage to Saturn. The voyage to Saturn was a two-part mission that included an orbiter and the Huygens probe. The Cassini orbiter was designed to explore Saturn’s system as it looped over, under, and around the planet’s many moons and rings. The Huygens probe was designed and planned for a study of the atmosphere and surface of Saturn’s largest moon, Titan, as well as a parachute-assisted soft landing on the surface. On September 15th the exploration phase of the Cassini mission will end as the spacecraft runs out of fuel and descends into Saturn’s atmosphere. As frictional forces tear the spacecraft apart, instruments on-board will send back data about the planet’s atmosphere.
35 Years Ago
   Typically, little is known about what happens after or before the active part of a mission. We know that the follow-up to a mission is the data analysis, which usually takes many years. What is generally not acknowledged is the lead-up to the official mission, which begins with the launch. The Cassini Mission was first proposed in 1982, 15 years before the actual launch. Several years of planning and coordination between NASA and the European Space Agency followed. By the end of the 1980’s, the mission had been approved and was finally launched in 1997. Thirty-five years will have passed since the inception of the Cassini mission and the demise of the spacecraft when it enters Saturn’s atmosphere.

    Where is Cassini Now?
    Cassini grand finale fact sheet
    Cassini mission
    Cassini mission timeline poster
    Four Days at Saturn video
    Grand finale


Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.

Saturn at West Quadrature

saturn-west-quadrature   Monday February 23rd, the position of the planet Saturn with respect to the Earth and the Sun places this ringed planet at what is called western quadrature. Saturn is at a 90 degree angle from us as this graphic shows. Think third quarter Moon as that is a fair comparison of the relative positions. At this position Saturn leads the Sun across the sky from east to west as the Earth is rotating, meaning that Saturn rises before the Sun and also sets before the Sun.
   Saturn currently is within the constellation of Scorpius the Scorpion as this graphic shows. From the northern hemisphere, looking toward the southern horizon, you can find Saturn above the reddish star Antares. Saturn shines with an apparent magnitude of around 0.5 compared with the 1st magnitude Antares.

Learn a little (or a lot) about Saturn by visiting the Cassini at Saturn mission web site.
Click here to go to the Cassini Mission web site.
Click here to go to the Cassini Mission Flyby web page to see when the next Saturn satellite flyby will be.

   This is a short 5 minute video I made as part of a live musical performance called “Orbit” that I was part of in May 2011. This is a piece from the much longer tour of the solar system performance and video and shows Saturn and some of its moons as viewed from the Cassini spacecraft that month.

Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Land of Many Lakes

titan   The only other place in the solar system that has liquid on its surface is Saturn’s moon Titan. However the liquid in the lakes on the moon Titan are not water as the temperatures on the surface average around -180o C (-292oF). Instead the liquid that falls as precipitation is in the form of methane, ethane, and other hydrocarbons. On Titan there is a cycle of evaporation, condensation, and precipitation that is reminiscent of the water or hydrologic cycle on our planet. Most of the liquids on Titan are found in the northern hemisphere.
   The NASA/JPL Cassini mission at Saturn folks just released a short video showing a simulated flyover of part of the region in the northern hemisphere of Titan where these lakes are located. Click here to go to the web site to see the flyover video as well as for additional information about the moon Titan. Click here to see the press release and to download the full picture of the moon Titan.
   Earth, by the way, is the only place we know of in the solar system where water is found in all three states of matter, at the same time.
   Saturn is currently in the morning skies rising about an hour before the Sun rises.
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

As the World Turns

   Today, January 19, the Sun is in two places at one time! The banner for this page was made using an Astronomy program and on this date the program showed that the Sun is entering the Astronomical Zodiacal sign of Capricornus, while according to the pseudoscience, astrology, the Sun is just entering the boundaries of the next constellation to the east – Aquarius. How is this possible?
   As the world turns, so does the sky, or so it appears to us from Earth. Our perspective of the sky is based in part on the Earth’s regular motions. Most of us are familiar with the concepts of rotation and revolution. Not everyone, though, is familiar with the less-perceptible Earth motion of precession. The Earth wobbles about its axis much the way a gyroscope does as it slows down. However, unlike a gyroscope, the Earth spins very slowly and will not stop spinning and topple over.

The Precession Circle

The Precession Circle

   The Earth’s wobbling motion is referred to as precession, or the shifting of the Earth’s axis over time. The wobbling is caused by a combination of its 23.5° axial tilt from the plane of the solar system, and the gravitational pull of the Sun and the other planets back toward the plane of the solar system. Because of the Earth’s rotational spin, it, like a gyroscope, resists outside forces, and does not align itself with the solar system.
   One way to visualize the changes caused by precession is to think about how the position of the Celestial Pole (the point in space directly over the Earth’s North Pole) moves with respect to the background stars. As the Earth precesses, the North Pole traces out a circle in the night skies, as does the South Pole. Presently, the Earth’s North Pole points almost directly towards the star Alpha Ursa Minor, commonly known as Polaris the North Star. Polaris is less than one degree from the North Celestial Pole. However, Polaris has not always been our North Star, nor even our brightest polestar. Several thousands of years ago the Star Thuban, in the constellation Draco the Dragon, was the Pole Star.
   The changing skies Precession is a slow but steady motion. The completion of one cycle takes about 25,800 years. As the Earth precesses, our view of the sky slowly changes, so that after a long period of time, the stars and constellations shift their positions in the skies relative to the Sun.
   Ancient cultures kept track of time by noting the Sun’s position with respect to the constellations. For example, the start of each season was identified by the Sun’s position within a constellation’s boundaries. However, due to precession of the Earth’s axis, this start position has shifted westward at over the centuries and in most instances is an entire constellation west from its position 3,000 years ago.

Position of Sun for Start of Each Season



(1000 B.C.)


(2000 A.D.)

Spring – March Aries Pisces
Summer – June Cancer Taurus
Fall – September Leo Virgo
Winter – December Capricorn Sagittarius

Click here to go to the Qué tal in the Current Skies web site for more observing information.

Saturn Rising

Saturn Meets Venus

   Following its solar conjunction during October the planet Saturn now moves into the pre-dawn morning skies on the western side of the Sun. As the Earth moves along its orbital path around the Sun, the Sun with its apparent motion along the ecliptic toward the east gives the appearance of moving away from Saturn. Gradually the distance between the Sun and Saturn increases resulting in Saturn rising earlier each day.
Try this: Observe Saturn at the same time each morning and you will notice that Saturn is appearing higher above the horizon at the same time.
   Venus is also on the move eastward and since its orbital speed is greater than the Earth and the Sun’s apparent speed it (Venus) will catch up with the Sun in the next month or so. Along the way Venus will pass by Saturn, coming within 1-degree, on the mornings of November 26th and 27th as this animated graphic shows. The graphic is set at 1 frame per day and shows the sky at 6:40 a.m. CST.

   The video below is a clip from a longer one I developed for a Planetarium performance last year. The longer video, Orbit, was part of a series of full-dome videos that were developed to be accompanied by original musical scores written by Daniel Eichenbaum, and performed live by Dark Matter under the 60-foot dome at the Arvin Gottleib Planetarium in Kansas City, MO.

Click here to go to the Qué tal in the Current Skies web site for more observing information.

Solar System Exploration @50

Cassini Mission Timeline

   This past August 27th marked 50 years of exploring the solar system by NASA. It was on that date in 1962 when the Mariner 2 Spacecraft was launched on a flyby mission of the planet Venus. To celebrate and acknowledge their achievements NASA is hosting a 2-day symposium in Arlington, VA on October 25-26. The symposium is open to the public with pre-registration required. Click here for more information about the symposium.

   Also celebrating an anniversary is the Cassini mission to Saturn. Launched on October 15th 1997 the Cassini spacecraft arrived at the Saturn system of ~63 moons in 2004 and has now been on duty for 15 years, although nearly half of that time was simply getting from our planet to Saturn. The mission is currently in its third phase or mission extension having started with the 4-year Cassini mission, followed by the 2-year Cassini Equinox Mission, and now the current Cassini Solstice Mission – scheduled to end around 2017.
   Among the accomplishments made by the Cassini mission include landing the Huygens probe on the moon Titan. According to a recent press release mission scientists have determined that the manner in which the probe landed suggests that the surface where the probe landed is soft, like “soft damp sand”.
   Click here to read the NASA press release.

Click here to go to the Qué tal in the Current Skies web site for more observing information.