The Parents' Review

A Monthly Magazine of Home-Training and Culture

The Evening Sky--September, 1890

THE SUN

On September 23rd the Sun enters Libra, crosses the equator, and Autumn commences.

THE MOON

Last quarter, 6th; new, 14th; first quarter, 21st; full, 28th.

It will have been noticed by those who have made use of the monthly star-maps in this magazine, or who are close observers of the evening sky, that the Moon does not rise always in the same place on the horizon. For instance, the full moon on July 2nd rose 24 - 1/2 degrees south of the equator, and on February 4th, 20 degrees north of it. In this month, September, the full moon is on the equator, and is therefore as long above the horizon as it is beneath it. As this date almost coincides with the autumnal equinox (which occurs on September 23rd), when the Sun is also twelve hours below and twelve hours above the horizon, it follow that for a few days the Moon rises as the Sun sets, and consequently there is no darkness at all, so that the work of reaping can be continued without interruption. Hence the full Moon which occurs nearest to the autumnal equinox is called the Harvest Moon.

In this month's map it can be distinctly seen how the Moon encircles the Earth once a month, and gets back to the same place in the heavens in a little more than twenty-seven days. But the full Moon on September 28th is not at the same place as the last full Moon on August 29th, which I have put in the map to make this explanation clearer. The reason of this is that the Sun has during the month moved forward among the stars a distance of one-twelfth of the heavens, therefore the Moon has to travel that distance before it puts us between it and the Sun again, and appears as full.

As the moon travels round the sky once in about 27-1/3 days, it will take her more than two days to cross this portion of one-twelfth, therefore the interval between two full Moons is about 29-1/2 days.

I also hope to explain by means of this map what is meant by the Moon's "nodes" and the Moon's "Inclination to the Ecliptic." The path of the Moon can be traced by its successive daily positions. The path of the Sun is represented by a red line, and is called the Ecliptic, the twelve principal constellations through which it passes being known as the Zodiac, which are easily remembered in their order by the old lines--

          "The Ram, the Bull, the heavenly Twins,
          And next the Crab the Lion shines;
          The Virgin and the Scales,
          The Scorpion, Archer, and He-goat,
          The Man that bears the watering-pot,
          And Fish with glittering tails."

These two paths of the Sun and the Moon do not run on the same lines, but form two great circles crossing each other at opposite points at an angle of five degrees. These points are called the "nodes," and where the Moon crosses the Ecliptic from south to north is the ascending node, while the decending node is where it returns to the south of it. These points are not always in the same place in the sky, but each node occurs more than a degree westward of the previous one, so that if the Moon be noticed to cross the Ecliptic near any bright star, or at any particular place, it will not be seen to do so again for eighteen years seven months, which is the time taken for what is called a complete revolution of the nodes.

The Obliquity of the Ecliptic may also be explained while we have it marked on the map. The Ecliptic crosses the Equator at an angle of 23-1/2 degrees, and its points of intersection also move along from year to year, but to such a small extent that the difference is scarcely perceptible. However, they are gradually travelling towards the west, and will complete the circle in 25,800 years. It naturally follows that if our Equator is being tilted up in relation to the Sun, our poles must also move in the same direction, and this accounts for our not always having the same Pole Star, for our axis swinging round with the Equator, points to different parts of the sky, which being traced among the stars would form a circle, also completed in 25,800 years. In about 12,000 years, Vega, the brightest star in Lyra, will be nearest to the North Pole, and will be used by the terrestrial astronomers of that day as the Pole Star, similar to the one in Ursa Minor which now serves us in that capacity.

There will be an occultation easily observed during this month. On September 27th the Moon will pass over 30 Piscium, a star of the fifth magnitude, at 10:36 p.m., which will again emerge at 11:45 p.m.

On September 29th, v. Piscium will approach very near to the Moon, being nearest at 7:18 p.m.

THE PLANETS.

Mercury and Venus are evening stars, and on September 1st set at 7:11 p.m. and 7:50 p.m. respectively, both being in Virgo.

Mars can still be seen in the evenings, as he sets at 9:51 p.m. on September 1st.

Jupiter is well-placed in the south at 9:31 p.m. on September 1st, and at 8:05 p.m. on September 30. Unfortunately he is low down in the sky, and not suitable for observations with small telescopes.

THE CONSTELLATIONS

Pegasus is in the meridian. Three of its stars and one belonging to Andromeda from a great square in the heavens, in which very few stars are visible, so that it is all the more striking. It contains a bright nebula with a blazing centre, which is resolvable into its component stars.

Typed by Whitney Townsend, April 2016