opposition – Page 2 – A Darker View

The Opposition Effect

It was pretty obvious, an odd bright spot in the trees below that followed the helicopter. Having educated myself on quite a few optical phenomena I knew exactly what it was I was seeing, and made a point of taking a few photographs.

The mechanism for this bright spot is remarkably simple… No shadows.

Called the opposition surge, Seeliger effect or shadow hiding this simple optical phenomena occurs when looking at rough or irregular surfaces that are directly away from the light source, usually the Sun. On an irregular surface some parts will shadow other parts, resulting in an apparent darkening of the overall surface. When looking at that part of the surface directly away from the light source no shadows are seen, making that region appear brighter.

Continue reading “The Opposition Effect”

Saturn at Opposition

Today the planet Saturn will pass through opposition, directly opposite the Sun in our sky.

Saturn 22Apr2010 — Saturn with Titan above

Saturn orbits the Sun once every 29.45 years. As the ringed planet continues on its way the Earth swings around much faster on our inside track. As a result we lap Saturn once every 378.1 days, passing between the planet and the Sun. During opposition Saturn will be well placed for observation all night long, rising at sunset, transiting at midnight, and setting at sunrise.

During opposition the planet and rings will be slightly brighter than normal, an effect known as the opposition effect. The effect is most notable in the rings where the apparent brightness can increase by 30%. The effect is a combination of two factors, shadow hiding and the retro-reflective properties of the ring particles.

Vesta at Opposition

Today the minor planet 4 Vesta will pass through opposition.

4 Vesta is one of the largest objects orbiting between Mars and Jupiter, a region often referred to as the Asteroid Belt. This is the second largest asteroid, at 530km (329miles) in diameter. It is also usually the brightest asteroid that can seen by earthbound observers. When Vesta is at opposition it is bright enough to be just visible to the unaided eye, usually around 6th magnitude.

This year Vesta will reach magnitude 5.7 at opposition. This magnitude requires a dark site to view without the aid of a telescope. Precise knowledge of the location is also helpful. Given these two items it becomes possible to see an asteroid with the unaided eye.

The minor planet is currently located in Virgo about 2.5° northwest of τVir. Interestingly enough the dwarf planet 1 Ceres will be located about 2° east and a touch south of Vesta. Despite being much larger than Vesta it will be over a full magnitude dimmer at about 6.9 magnitude.

Vesta was visited by the Dawn spacecraft during 2011 and 2012. Dawn is now on course for Ceres with a planned rendevouz in February 2015.

Vesta 28May2007 — Vesta (marked), Jupiter and Summer Milky Way, 40s, 17mm@f/4, fixed tripod on 28May2007

Uranus at Opposition

Today the planet Uranus will pass through opposition, directly opposite the Sun in our sky. The planet will be well placed for observation all night long, rising at sunset, transiting at midnight, and setting at sunrise. If you are looking to observe Uranus, it is currently shining at magnitude 5.7 in the center of the constellation Pisces.

Neptune at Opposition

Today the planet Neptune will pass through opposition, directly opposite the Sun in our sky. The planet will be well placed for observation all night long, rising at sunset, transiting at midnight, and setting at sunrise. If you are looking to observe Neptune, it is currently shining at magnitude 7.8 in the center of the constellation Aquarius.

Saturn at Opposition

Today the planet Saturn will pass through opposition, directly opposite the Sun in our sky. The planet will be well placed for observation all night long, rising at sunset, transiting at midnight, and setting at sunrise.

Saturn at Opposition

This morning, at 07:44HST, the planet Saturn will pass through opposition. Earth will pass between the outer planet and the Sun. During this time Saturn rises at sunset, transits at midnight and sets at dawn. The planet is perfectly placed for observation, high in the sky, for much of the night. You can find Saturn in Virgo, five degrees from the bright star Spica.

For a few days before and after opposition the planet and it’s rings will be a bit brighter, an effect called, appropriately enough, the opposition effect. This is because we are directly in line with the Sun and planet, minimizing any shadows on the planet and in the rings.

Mars Close Approach

Today the planet Mars will be at its closest point to the Earth.

Mars was at opposition two days ago, but not at its closest. Close approach of the two planets is not necessarily on the same day as opposition, but can vary up to two weeks. This year sees the two planets approaching to 99,331,411 km (61,721,554 miles) at 07:01HST. At this distance the red planet will show a disk 13.89″ arc-seconds across in the eyepiece.

All month Mars will be visible throughout the night, high in the sky at midnight. This is the time to enjoy observing our closest neighboring planet while it is nearby and high in the night sky.

Mars Opposition

Today the planet Mars will pass through opposition.

Closest approach of the two planets is not necessarily on the same day as opposition, but can vary up to two weeks. This year closest approach will occur March 5th with the two planets approaching to 99,331,411 km (61,721,554 miles) at 07:01HST. At this distance the red planet will show a disk 13.89″ arc-seconds across in the eyepiece.

All month Mars will be visible throughout the night, high in the sky at midnight. This is the time to enjoy observing our closest neighboring planet while it is nearby and high in the night sky.

Mars Opposition Reminder

One week from today, on March 3rd, the planet Mars will pass through opposition.

Mars orbits the Sun every 1.88 years, with Earth only taking one year for each orbit. Like two runners on a track the two planets race each other around the Sun. But we have the inside lane, lapping the red planet every two years. These events are called opposition, when Mars is closest to us and best positioned for viewing by earthbound telescopes.

Closest approach of the two planets is not necessarily on the same day as opposition, but can vary up to two weeks. This year closest approach will occur March 5th with the two planets approaching to 99,331,411 km (61,721,554 miles) at 07:01HST.¹ At this distance the red planet will show a disk 13.89″ arc-seconds across in the eyepiece.²

Mars during the 2005 opposition

Do not worry about viewing on the 3rd or 5th, any time in the month leading up to and after opposition the viewing will be very good. With even a modest telescope it should be possible to see the bright polar caps and light and dark markings on the planet.

All month Mars will be visible throughout the night, high in the sky at midnight. This is the time to enjoy observing our closest neighboring planet while it is nearby and high in the night sky.

1) 2012 Mars Opposition at SEDS
2) The 2012 Aphelic Apparition of Mars