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Ephemeris, AppearancePlanisphere

2.2 The PlanetChart and EclipticChart Functions

PlanetChart produces a graphic showing a calendar of planetary events for a specified year. You can use this function to make a wall chart.

Charting planetary positions for a year.

To use the chart, select the date from the left-hand side, and read horizontally across to find a particular planet. Planet images are sketched at the top and are labeled in the key at the bottom. Once you locate the point on the planet line, use the colored diagonal bands to determine whether the planet is visible in the evening or morning sky. Read vertically from the point to the ecliptic line in the star field to find where the planet is in relation to the stars on the specified date.

There is a wealth of information contained in the chart. It shows new, full, and half moons, along with any lunar eclipses that might occur during the year. In addition, annual meteor showers are represented as large green objects and are placed so as to indicate the date and star field position where you might be able to see them. Other features of the chart include a diagonal scale, labeled on the right-hand side, that you can use to determine rising and setting times for the planets. You can also use the chart to indirectly find the local horizon at any given hour in relation to the stars in the star field. Because the chart is independent of your latitude, you can use it anywhere in either the northern or southern hemispheres.

Here is the planet chart for 1994. Select the date from the left-hand side, and read horizontally across to find the planet of interest. Use the colored diagonal bands to determine whether the planet is visible in the evening or morning sky. Read vertically downward from the point to the ecliptic line in the star field to find where the planet is in relation to the stars on the specified date.

In[14]:=PlanetChart[1994, TextStyle -> {FontSize -> 8}];

Here is the kind of information that you can extract from the chart shown for 1994.

In the first month of 1994, all the major planets, with the exception of Jupiter, are behind the Sun. Jupiter rises in the morning about 4 to 6 hours before sunrise and is visible in the constellation of Libra. Later in the year, during the month of October, Jupiter and Venus are in conjunction and are visible in the evening sky for about 3 hours after sunset each night for two weeks. At the same time, Mercury is at its maximum eastern elongation from the Sun, which happens once every four months. You should be able to spot all three planets at the same time and in roughly the same place. Later in October, there is a meteor shower in the early morning hours, visible in the direction of Orion. At the same time, there is a full moon about 60 degrees, or 4 hours of right ascension, away in the constellation of Pisces. The full moon may make it difficult to see some of the less bright meteor trails. While waiting for that shower, you may try to find Mars in the constellation of Cancer, by looking about 45 degrees away to the east. It only rises above the horizon at about 5 hours before sunrise, so you will have to stay up late to see it. One other notable feature for 1994 is a lunar eclipse near the end of May. Like all lunar eclipses, it is visible from one side of the Earth only, where it can last for up to two hours.

The EclipticChart Function

A brief guide to the main stars spread along the ecliptic line is shown at the bottom of the planet chart output. The EclipticChart function displays only that guide, which you can print and use for reference.

Generating a chart of the zodiac constellations.

EclipticChart shows the stars along the ecliptic line.

In[15]:=EclipticChart[];

The key constellations to remember are Orion and Scorpius, which are in opposite parts of the sky. At any time of the night at least one of these constellations is visible. Orion is dominant in the evening sky during the beginning and end of each year. Scorpius is dominant in the evening sky during the middle of each year.

Ephemeris, AppearancePlanisphere



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