A Course in ASTRONOMY AWARENESS

UNIVERSITY OF THE THIRD AGE

Introduction to the Solar System

Ever wonder how we live and exist in a vast universe ?

This course will outline our home, the Solar System and describe some scientific facts and interesting aspects about it. The most important star is our Sun and you will learn about this giant body and perhaps be able to safely witness sun spots on its surface.

I will progressively move out from the Sun and describe and illustrate each planetary body including Mercury, Venus, our Earth & Moon, Mars and its two tiny moons, Jupiter and its numerous moons or satellites, Saturn its rings and satellites, Uranus, Neptune, and the outermost planet (?) Pluto. There are marvellous illustrations of these bodies from the NASA space program, but to observe them yourself can be even more fascinating even though they all look much smaller except when seen with the largest of telescopes. The course will include some information on bright comets this century and how to observe them as well as meteor showers from cometary tails and the asteroids lurking between Mars and Jupiter and those which may approach the Earth.

Some simple observing hints will be given and a where, when and how description for the next partial lunar eclipse which will be visible from Canberra in the early evening of Wednesday 1999 July 28. Observatory trips can be arranged particularly at the Mount Stromlo Observatory - Stromlo Exploratory, and to the new Canberra Planetarium and of course to my private observatory in Calwell.

Information on the local amateur astronomy group will be included for those keen to continue with Astronomy.

Byron Soulsby

Astronomy Awareness

Course leader

02 6292 6591

Size of the Planets

In these notes there is a model of the Solar System where the distances between the planets are placed on a Map of Canberra to scale, to indicate the vast distances between each planetary body.

The actual observed size of the planets change throughout the year as their distances vary from the Earth, for instance, Jupiter appears larger (49.6 seconds of arc , or ") in October 1999 than in January (35.3 "), Saturn appears largest in November (20.3 ") and smallest in May this year. The greatest apparent change in observed size is in the planets nearest the sun with Mercury, in the evening ranging from the smallest size in January this year (4.7 ") to the largest in July (11.0 "). Venus also changes dramatically as seen from the Earth from August (58.3") with the largest crescent from the smallest in January this year (10.3 "). Mars is in opposition with the earth at 16.2 " on May shrinking to 5.0 " in December, but the gaseous giants beyond Mars change much less as their distance from the Earth do not vary much in any one year.

The mass of the planets vary greatly and while the ratio of masses of Earth to the Moon is 81.3, that of the Sun to the Earth is a whopping 332,900.

Observing

To observe the planets and many of their larger satellites, a steady telescope is best, even for our Moon. It is probably impracticable to view good images of the outer planets, with the exception of Jupiter and Saturn as most are very difficult to locate and appear extremely small in small telescopes or binoculars.

For instances the Moon subtends an angle of around 0.5 of a degree when seen from the Earth, and with 7 X 50 to 10 X 50 binoculars this can be enlarged to say seven to ten times this to give an apparent size of 3.5 to 5 degrees, which is large enough to identify some craters on its surface such as Tycho and Plato - see the map of the Moon.

The outer planets are only a fraction of this size. For Jupiter with its size at its best position now in August at 49.7 minutes of arc, this planet can be enlarged to 0.1 to 0.15 degrees in your binoculars, which is insufficient to see any details at all. But when seen through a modest telescope say at a magnification of 350 times, this swells Jupiter's size to an apparent 4.7 degrees which is near the binocular size of the Moon. Through such a telescope the wonders of Jupiter and its four largest satellites or moons, are revealed, showing the atmospheric banding, the giant red spot and its satellite shadows and their mutual occultations and transits are easily seen. The Moon is magnificent at this high magnification and detailed studies can be conducted - more on this later.

The Sun our nearest star does often have some interesting features and if the weather is clear we will safely project the sun's image from a small telescope to see if there are any sunspots, perhaps similar to those shown below:

For Mercury we can best see it on the rare occasion of solar transit as shown here in this Calwell Lunar Observatory original positive image. Mercury is shown as the small black dot one third up from the bottom of the image and near the limb of the Sun. This year there will be another transit of Mercury in the early morning of November 16 starting at 8h 18.5m and ending at 9h 4m am local summer time.

For Jupiter we can best see it through a large telescope such as the Yale-Columbia 26 inch refractor at Mount Stromlo Observatory, as shown in this Calwell Lunar Observatory video image on the left at the time of impact of one section of comet Shoemaker-Levy 9 also shown in the ABC video image on the right:

However, for Mars telescopic views can be disappointing, but this year the maximum size in a 350 X telescope will be near 16 minutes of arc which is apparently only a quarter of the binocular sized moon. However, as Mars has very little atmosphere and if its surface is not suffering from dust storms it will be possible on a very clear and windless night to see some of its surface markings, such as Sinus Sabæus.

A recent NASA space probe to Mars, the Pathfinder has provided exciting views of the planet's surface as shown below.

The atmosphere of our planet can cause havoc when observing the planets as small air turbulence can badly affect the seeing.

A model of the solar system placed on a map of Canberra

The distance between the outer planets of the solar system is shown to scale on this map of south Canberra. With the Sun at Capital Hill, Mercury is at Parliament Drive (0.17 km), Venus at Capital Circle (0.32), Earth & Moon at State Circle (0.45), Mars at Windsor Walk (0.68), Pallas at Manuka Oval (1.5), Jupiter at Red Hill Kiosk (2.3), Saturn here at the Hughes Community Centre (4.3), Uranus at Stirling College (8.5), Neptune at Bonython oval (13.4) and at its mean distance Pluto at Mount Tuggeranong (17.6 km). The diameter of my Earth model is 3.8 cm, with the size of the Moon at 1 cm and 114.5 cm away with the Sun model 4.2 metres in diameter. The overall solar system model scale is 1 to 2.98 X 10 to the - 9.

Observing Charts

I have used Voyager software to produce observing charts for each week of this course. The first, is for the visible planets on Monday 1999 May 10 at 10:30 PM. This chart is when the Sun is well below the local horizon with some of the planets set , but Jupiter, Mercury and Saturn can be seen as shown at the far left of this chart. The visible planets shown are all well above the horizon, but may be difficult to see except in a large telescope. The Moon is shown on the lower right and abbreviated constellation names are included. Look for the partial lunar eclipse on the evening of July 28. I will say more about that eclipse at our last session.

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Here is a short calendar of interesting astronomical events for May and June this year, courtesy of the

Mars Pathfinder

The recent Mars Pathfinder space probe has provided us with some magnificent pictures. The first is of the Mars landing site from the Hubble Space Telescope:

And here is one of the first images of the surface of Mars from the Pathfinder after it had successfully landed on Mars on 1997 July 4. Note the red sky and an apparent "cloud" cutting into the left side of the mountain on the horizon (however, NASA says this is an image artifact):

Here is another of the images of the surface of Mars from the Pathfinder after it had successfully landed on Mars on 1997 July 4. Note the large surface boulders near the landing site in the dry flood channel named Ares Valles. The boulders probably represent deposits from one of the catastrophic floods that carved the ancient channel. :

Here is the first image of a PROTOTYPE PLANET as discovered by the Hubble Space Telescope:

Hubble Takes First Image of a Possible Planet Around Another Star and Finds a Runaway World

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