Picture of the Moment...

Please find a picture of topical interest, which I will change on a fairIy regular basis. Most likely a recent celestial event but could be somewhere interesting I have been recently.


A quick tour of the Solar System

Four planets and three moons, 9 Apr 2004

During April and May 2004 four of the five naked eye planets are gathered together for convenient viewing as soon as it gets dark in the evening. On the 9th April I attached my Philips ToUCam Pro webcam to my 8-inch telescope to take a tour of them.

With the exception of Mars, which received attention last autumn, this was the first time I have used the webcam on the other planets, and I am amazed at the quality of Jupiter and Saturn, and pleased that their moons have come out so well too. All planets are presented at their actual sizes as seen by the webcam (0.3 arc seconds per pixel), though of course their different distances (quoted below for 9th April 2004) hides their true sizes. North is up and East is left, so the sun shines from the right.

Moving outwards from the Sun...

  • Venus is 12,104 km in diameter (almost the same as the Earth) and is also the closest at 95 million km.
  • Mars is 6,794 km in diameter (half the size of Venus) but lies at 300 million km, so appears tiny by comparison.
  • Jupiter is the largest planet, with a polar diameter of 134,200 km (11 times that of the Earth), and lies at 693 million km. Its fast rotation period of only 10 hours gives it a noticeable equatorial bulge, and also visible in this shot is the Great Red Spot, a storm that has been raging for over 300 years. Two of its moons are visible, Io and Europa, both of which are similar in size to our own. With the fast rotation period, turbulent weather systems and 4 bright moons whirling around the planet there is always something to see, as this animation from 16 May 2004 shows.
  • Saturn is the second largest planet with a polar diameter of 108,000 km, but lies at 1,377 million km, nearly twice the distance of Jupiter. However,its magnificent ring system makes up for the smaller size of the planet. The moon Titan is 48% larger than our own.

Of course the planets are not really this close together in the sky - to see where they really were see this picture I took on 24th April, looking west at 8.20pm BST. On this evening the crescent Moon (heavily over-exposed in the picture) passes through the group, but Jupiter is high in the south so is not possible to include in the same shot.

Picture added on 1 May 2004


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