Equality at Sunset

9 p.m. CDT

9 p.m. CDT

   An interesting arrangement of the two largest planets in our solar system, Jupiter and Saturn, is taking place at sunset local time. Jupiter and the last of the winter constellation are over the western horizon as it is setting. While above the eastern horizon is the planet Saturn as it rises with the stars of spring. For the next few evenings each planet will be approximately the same altitude above their respective horizon at 9 p.m. local time as the banner graphic at the top of the page shows.

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

Which Way Are You Going?

   This semester I have a Physical Science class in addition to my Astronomy class and during last night’s discussion about speed and acceleration I mentioned that the speed of an object is always relative or with reference to something else. I even added that “quote” from Einstein’s mother, “Everybody is a relative.”
4 motions   Seriously, in discussing this I dipped into Astronomy and talked about how the Earth and other planets in our solar system all have at least 4 general motions relative to the Sun and the galaxy. And that even the galaxy is in motion and its speed is also relative. On the Earth we rotate (1,000 mph at the equator); we revolve around the Sun (67,000 mph); along with the rest of the solar system we are following the Sun toward the star Vega (43,920 mph); and with regard to the galaxy we are revolving around the galactic center (483,000 mph) as are other stars in the galaxy.
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.

Is Earth A Dwarf Planet?

   The title is sort of misleading but after reading a press release from the NASA WISE (Wide-field Infrared Survey Explorer) mission I started thinking about the IAU official definitions for a planet that distinguishes a planet from a dwarf planet. In particular definition # 3. (see below) This thinking resulted from reading the press release which described success in determining the colors of the Trojan Asteroids that orbit at two specific points along Jupiter’s orbital path. I thought, “wait a minute”, if a planet had to have cleared its orbital path (# 3) then Jupiter with these Trojan Asteroids, and in fact Earth, Mars, and Neptune with their own Trojan Asteroids, may need to be considered as dwarf planets — by the definition.
   However the authors of the definitions took these Trojan asteroids into consideration and as the full definition explains there may be objects like the Trojan Asteroids that while orbiting the Sun along a planet’s orbital path, these objects are where they are as a result of gravitational interactions or orbital resonances with that planet, Jupiter for example. The bottom line is that there are no other objects along Jupiter’s orbital path other than those placed and held there by Jupiter’s gravitational field. And the same applies to Mars, Earth, and Neptune. Interestingly there are even moons having Trojan Satellites.
   Is Earth a Dwarf Planet? No, it is one of the 8 planets in our solar system.

   The Trojan Asteroids near Jupiter are interesting in many ways including that they are different from the asteroids we find in the main asteroid belt for example. The colors of these Jupiter Trojan asteroids are also different. Did you know that asteroids had color? Jupiter has two pair of Trojan asteroids – both at the same angle from Jupiter with one leading and the other trailing Jupiter.

  1. Orbits the Sun
  2. Has enough mass to have a spherical or round shape (at or near what is called hydrostatic equilibrium)
  3. Has cleared its neighborhood – objects along its orbital path.

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