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November 20 moon near First Point of Aries

Tonight's moon is near on our sky's dome to the March equinox point, or First Point of Aries.

Tonight for November 20, 2015

Tonight – November 20, 2015 – the moon is near the First Point of Aries, one of two equinoctial points on the imaginary celestial sphere surrounding Earth. The First Point of Aries is where the ecliptic and sky’s equator intersect. The ecliptic is a projection of the Earth’s orbital plane upon the celestial sphere. The celestial equator is a projection of the Earth’s equatorial plane upon it. If you were to imagine breaking up the sky into a grid surrounding Earth – marking lines of celestial latitude and longitude – the First Point of Aries would mark the zero point of longitude in our sky.

There’s no grid in the sky, anymore than there is on Earth, but these imaginary lines are of use to astronomers – just as earthly latitude and longitude are useful. The First Point in Aries marks that special point on the stellar sphere where the sun crosses the celestial equator on the March equinox, going from south to north.

In the sky, as on Earth, everything is always moving and shifting. The motion of precession has carried the First Point in Aries out of the constellation Aries.

The point is now defined as the northern vernal equinox point in the year 1950. Because of precession, if you could see the stars during the day, you’d see the March equinox sun in front of the constellation Pisces the Fishes, to the south of the Square of Pegasus.

On these next few nights – November 20 and 21, say – use the moon to help you envision the First Point of Aries, and then – once the moon has moved from this part of the sky – rely the Square of Pegasus to find the point again.

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The celestial meridian (0 hours right ascension), the ecliptic (0o ecliptic longitude) and the celestial equator (0o declination) intersect at the March equinox point.

The celestial meridian (0 hours right ascension), the ecliptic (0o ecliptic longitude) and the celestial equator (0o declination) intersect at the March equinox point.

Now let’s consider the path of the moon. Its orbital path is inclined at 5o to the plane of the ecliptic. Twice a month, the moon crosses the ecliptic at points called nodes. This month, the moon will cross the ecliptic going from north to south (at the moon’s descending node) on November 21 at 13:56 Universal Time.

And at this time, the moon will very nearly align with the First Point of Aries.

Node passages of the moon: 2001 to 2100

In ancient times, the March equinox sun shone in front of the rather small constellation Aries the Ram. That’s why, in newspaper astrology columns and elsewhere, you often see Aries at the top of the Zodiac – the band of stars that provides a backdrop for the sun in the course of every year, and the moon in the course of every month.

Aries often comes first in lists of zodiacal constellations because it marked the sun’s location at the time of the Northern Hemisphere’s spring equinox between 1866 B.C. and 68 B.C. Its relationship to the coming of spring gave this point vast significance to early astrologers. That relationship was so significant, in fact, that the point retains the name First Point in Aries – even though the actual location of the sun at the time of the Northern Hemisphere’s spring or vernal equinox has shifted into the constellation Pisces, due to precession.

The first point of Aries – or the position of the March equinox point relative to the backdrop stars – slowly but surely drifts westward through the constellations of the Zodiac, going full circle in about 26,000 years.

Image via Wikimedia Commons

When does the Age of Aquarius begin? Click here. Image of Leonardo da Vinci’s famous Vitruvian Man via Wikimedia Commons

So, naturally, the point is still moving. According to astronomers, we won’t enter the constellation Aquarius – and thus enter the age of Aquariusfor centuries to come.

It’s good to recall here that constellation boundaries were not always hard and fast. The current boundaries for the constellations were decided upon as recently as the 1930s by members of the International Astronomical Union.

When does the Age of Aquarius begin?
Bottom line: This post contains an explanation of the First Point in Aries and also speaks of the Age of Aquarius.

Aries? Here’s your constellation

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