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{ Practical astronomy | Astronomy | Planets }


Planets

Conjunctions

planets at dawn
Saturn, Venus and Mercury at dawn.

Left: On our sky, all planets stay close to a great circle called the "ecliptic", and so it is common for several planets to come relatively close to each other. The field of view here is about 10°.

Edinburgh. f = 55 mm, f/5.6, 10 s, 400 ISO. Canon EOS 400D.

close conjunction of Venus and Mercury
Conjunction of Venus and Mercury, 2005-06-27.

Right: Rarely come two planets this close, just under 4' separate Mercury from Venus. There is no danger of a real collision, because they are at vastly different distances. The sky is a bright blue, because this image is taken around teatime in bright sunlight.

Edinburgh. f = 4000 mm, f/20, 1/640 s, 400 ISO. Celestron 8, Canon EOS 300D.


Transits

transit of Mercury
Mercury transit 2003-05-07.

transit of Venus 2004
Venus transit 2004-06-08.

transit of Venus 2012
Venus transit 2012-06-06.

Top: Occasionally, Mercury, which orbits the Sun inside the Earth's orbit, moves in front of the Sun, a bit like the Moon does in a solar eclipse. Although Mercury is bigger than the Moon, it is a lot further away, so it appears quite small compared to the Sun. The transit of Mercury in front of the Sun takes several hours. In the image the transit is about to end. Ten minutes later and all will be over. Mercury is the small dark circle. The dark area on the right is the blank sky, and the bright area on the left is the Sun. You can see the curvature of the solar limb, which gives an indication that the Sun is more than 100 times bigger than Mercury. At the Sun's distance the Earth would have an apparent diameter of about 18", which is not much more than the 12" diameter of Mercury in this image.

Edinburgh. f = 4000 mm, f/20. Celestron 8 with Solar Skreen filter, Philips ToUcam Pro. Unsharp mask.

Centre: Occasionally, Venus, which orbits the Sun inside the Earth's orbit, moves in front of the Sun, a bit like the Moon does in a solar eclipse. Although Venus is bigger than the Moon, it is a lot further away, so it appears quite small compared to the Sun. The transit of Venus in front of the Sun takes several hours.

Edinburgh. f = 400 mm, f/6.3, 400 ISO. Telephoto lens with Baader foil filter. Canon EOS 300D.

Bottom: The Venus transit of 2012-06-06 was visible only during the final hour or two from Europe. As the Sun rises sooner further east, I travelled from Scotland to Northern Germany to observe it. The weather was not good, but better than back at home.

To me it appeared that cloud was too thick after the first minute of the Sun emerging from the distant treetops. But close inspection of some of the images I took anyway allowed me to measure the distance of Venus from the solar limb on 12 occasions. The results are mildly sensitive to the ratio of the Earth's size and the dimensions of the Solar System. Thus I was able to determine the Astronomical Unit - the mean distance between Earth and Sun - to be 143 ± 10 million km. Even in 1761 and 1769, the concerted effort of the planet's astronomers did better at 153 million km; the modern value is 149.59 million km.

Heilshorn, Germany; Canon EOS 400D; f = 800 mm; f/12.6; 100 ISO; 0.25 s (no filter).


Telescopic views of classical planets

Venus
Venus 2005-12-24.

Mars
Mars 2005-11-18.

Jupiter
Jupiter 2003-02-12.

Jupiter
Jupiter 2004-05-01.

Saturn with open ring
Saturn 2005-03-08.

Saturn with ring edge-on
Saturn 2009-03-19.

Top: The planet Venus is the Earth's inner neighbour. This image shows a thin crescent phase.

Edinburgh. f = 4000 mm, f/20. Celestron 8, Philips ToUcam Pro. Unsharp mask.

Second from top: The planet Mars is the Earth's outer neighbour. This image shows dark highlands and bright lowlands. Also the extensive cloud in the north (blue/white, top right).

Edinburgh. f = 4000 mm, f/20. Celestron 8, Philips ToUcam Pro. Unsharp mask.

Third from top: The giant planet Jupiter has a very lively atmosphere. Most prominent are the two dark bands north and south of the equator. Left of centre in the southern band is the Great Red Spot.

Edinburgh. f = 4000 mm, f/20. Celestron 8, Philips ToUcam Pro. Unsharp mask.

Fourth from top: The giant planet Jupiter has a very lively atmosphere. Here the bands show more structure and dynamic. The Great Red Spot is to the far right here.

Edinburgh. f = 4000 mm, f/20. Celestron 8, Philips ToUcam Pro. Unsharp mask.

Second from bottom: In 2005, Saturn's ring is wide open with the Earth on its southern side. The Cassini division in the ring is clearly visible.

Edinburgh. f = 4000 mm, f/20. Celestron 8, Philips ToUcam Pro. Unsharp mask.

Bottom: In 2009, the Earth is close to switching from the southern to the northern side of Saturn's ring.

Edinburgh. f = 4000 mm, f/20. Celestron 8, Philips ToUcam Pro. Unsharp mask.