Jupiter at Opposition: 2017

Zooming in on Jupiter at Opposition   Friday April 7th, the outer giant planet Jupiter reaches the point in its orbit around the Sun that places the Earth in between Jupiter and the Sun. This is known as opposition, and opposition is an orbital position that applies to solar system objects (outer planets, dwarf planets, asteroids, comets, etc.) orbiting the Sun beyond the Earth’s orbit. An object at opposition will have approximately the same heliocentric longitude as the Earth’s heliocentric longitude. So on Tuesday both planets will have a heliocentric longitude of about 167o.
   An opposition of Jupiter occurs approximately every 13 months because both Earth and Jupiter are moving. After one Earth Revolution, an Earth year, the planet Earth will be where it was the previous year at opposition with Jupiter. However Jupiter will not be there because it has moved during the past year as well. It will take the Earth about an extra month or so to catch up with Jupiter. Earth moves 360o each year while Jupiter moves approximately 12o each Earth year.

Sunset Local Time

Sunset Local Time

   When an object is at opposition it rises at approximately the same time as local sunset and that same object at opposition sets at approximately the time of local sunrise. In other words an object at opposition will be up all night from sunrise to sunset.
   Picture our Moon at full phase and how it is directly opposite the Sun, with the Earth in between. The full Moon in effect is at opposition but we call it the full Moon instead. And like Jupiter at opposition, a full Moon rises at sunset, sets at sunrise and is visible all night.

   Jupiter rising with Spica.
Take a brief tour of the Jovian (Jupiter) system. Music by Dark Matter.
Live recording of music written by Richard Johnson. Video by me!


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.

April Moon at Ascending Node

   Friday April 7th the waxing gibbous Moon will be crossing the plane of the ecliptic moving north relative to the ecliptic. This is known as the ascending node, one of two intersections the Moon’s orbital path has with the ecliptic. The ecliptic is actually the Earth’s orbit and the Moon’s orbit is inclined about 6o from the ecliptic. So there are two node intersections, the ascending and descending nodes.

   On April 7th the 11-day old waxing gibbous Moon will rise with the constellation Leo the Lion and is located near the Lion’s tail, the star Denebola.

   Does our Moon actually go around the Earth as many graphics show? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*

*Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”


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.

A Night With the Lion

   Thursday evening April 6th and Friday morning April 7th the waxing gibbous Moon will rise and then set with Regulus, the brightest star in Leo the Lion. During the course of the night the Moon will pass within about 1o-2o from Regulus.

   Thursday evening April 6th, after sunset, look toward the west for a reddish appearing star. That is the planet Mars and about 2o to the east, left side, from Mars is Dwarf Planet Ceres, the closest of the dwarf planets. Not sure about Mars? Look for the Pleiades, an open star cluster with the brighter stars having a small dipper shape. Below the Pleiades is Mars.

   Thursday evening April 6th at sunset it may be possible to see the innermost planet Mercury in addition to seeing Mars and Jupiter, and at least with binoculars Dwarf Planet Ceres.


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 Begins Retrograde Motion

   Thursday April 6th the outer planet Saturn begins its retrograde motion. This is an apparent motion that Saturn or any outer planet, dwarf planet,or asteroid has when compared to the faster moving Earth. The Earth, moving more quickly around the Sun than an outer object, will catch up and pass by the outer object sort of like a car passing a slower moving car.
   As the faster moving Earth passes by, the outer object appears to stop its eastward direct or prograde motion, and then moves westward, or retrograde, for a while until it again stops before resuming its prograde motion. Saturn will remain in retrograde until June and will travel westward out of Sagittarius the Archer into the boundaries of Ophiuchus the Healer.


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 and Some Messier Objects

   In the early morning hours before the Sun rises the summer (northern hemisphere) Milky Way arches across the sky from the southern horizon toward the northern horizon. Over the southern horizon is the constellation Sagittarius the Archer and the direction toward the center of the Milky Way Galaxy. In this direction is the planet Saturn and within the field of view of binoculars are several nebula, some of which are visible to the naked eye.
    Despite the use of optical aids like binoculars or telescopes we do not see the colors of these object that you may see in photographs. Regardless, this part of the sky is filled with many objects visible to the naked eye and certainly with binoculars. And assuming the local skies are relatively dark then viewing this area of the Milky Way will provide many viewing rewards.


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.

Congress Downsizes the Solar System

   The US Congress today, in an effort to rectify the current sequestration budget cuts has made a dramatic announcement. In an effort to reduce the NASA budget, a resolution was passed today to downsize the solar system. According to an unnamed congressional staffer, House Republicans felt there has been “too much redundancy in the solar system” and that streamlining the 4.5 billion year old planetary system is long overdue. Such action would give NASA fewer places to go and this would allow the agency to carry out its space exploration goals within the funding profile that the House proposed earlier this summer.

   “Look, we have four terrestrial planets” said Congressman Rip U. Apart (R, OK), “and only one of them really works! So why not get rid of at least two of the others and clean up the neighborhood?” Most subcommittee members felt that while downsizing was definitely in the cards, eliminating both Mercury and Venus, or even Mars, was going too far. “We have too many international commitments to Mars.” said another politician. “So I think we should keep Mars and dump Venus and Mercury. It’s too hot to live on Venus, and liberal Democrats keep using it as an example of what climate change can do. So from a political and practical point of view, Venus has got to go.”

   Definitely at risk is the planet Mercury which lacks support because of its small size and poor visibility from Earth. “Who needs it?” asked Congressman Newt Onian (R, N.C.). “Have you ever seen it? I haven’t. So what good is it? We just don’t need useless planets. And speaking of useless planets, what about the asteroids? If you’ve seen one, you’ve seen them all. So I say we ought to get rid of the little boogers once and for all.”

   However, the downsizing recommendations do not stop with the terrestrial planets. The resolution also calls for a reduction in the number of gas giants which contain most of the planetary mass in the solar system. Most subcommittee members favor retaining Jupiter and Saturn, and eliminating Uranus and Neptune. “Jupiter employs the most molecules, and Saturn has those pretty little rings everyone likes.” said Rep. Con Mann (R, Fla.). “On the other hand, Uranus is a bore and its rings are dirty. And Neptune, for God’s sake, is just too far away.”

   The subcommittee was unanimous in its views towards Pluto which they deemed a moral misfit. “Now here’s a planet we can definitely do without.” continued Fornow. “Several years ago it was farthest from the sun (1979-1999), and now it’s not. It’s just too confusing. And now they tell me it’s really a Dwarf Planet. What the heck is going on here?”

   The resolution must now be presented to the entire House, where it is expected to pass easily since only a minority of Representatives have constituents on the affected planets. NASA Administrators have vowed to resist any further reductions to the solar system, saying that “NASA has expended considerable effort to make solar system exploration cheaper, faster, and better. Much of this work would be wasted if the solar system were downsized.”

   Critics say, however, that reducing the number of planets will not produce the expected savings to taxpayers. Textbooks, they note, would have to be revised to reflect the new arrangement, and facilities would need to be constructed to remove the planets themselves.

   April Fools!!


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.

Taurus Takes It On The Chin!

   Friday evening March 31st the 4-day old waxing crescent Moon will be about 4o from the reddish star Aldebaran in the open star cluster The Hyades. This open star cluster has a noticeable v-shape and from mythology the v-shape is the face of Taurus the Bull. Over the course of several hours as the Moon continues moving eastward along its orbit the Moon will pass across the v-shape and will be less than one-half degree from Aldebaran.
click on animated graphic to see it larger
   From my longitude this part of the sky will have set but observers in parts of north Africa, India, and that part of the world may be able to see an occultation of Aldebaran by the Moon. This animated graphic shows the Moon’s motion from 9 pm CDT 31 March to 5 am CDT 1 April (2 UT 1 April to 9 UT 1 April).

   The point of the v-shape is the bull’s nose while the two stars at the open end, Aldebaran and Epsilon Taurus mark the bull’s eyes. To the right, west, from the Moon is another open star cluster The Pleiades.


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.