Astronomy 101 for Writers: 1. Astronomy 101 for Writers

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1. Astronomy 101 for Writers

Astronomy seems to be a mysterious subject to many people and confusing issues such as moon phases and the motions of Venus can be tricky enough to cause some folks to leave them out altogether. However, including a mention of the celestial bodies in one's story can add a wonderful level of realism. This article attempts to provide some general information in easy-to-understand language to help writers add realistic astronomical details to their stories.

Moon phases:

Each stage represents about 1 week of the Moon's roughly 28 day cycle. The rise and set times below are general; actual rise and set data can be found in an almanac and can vary by a few hours from what is mentioned here. Online almanac

1. The New Moon is roughly in-line between the Earth and the Sun. It moves with the sun across our sky, and as the illuminated side is facing away from Earth anyway, it is not visible at all except on the rare occasion of a solar eclipse.
The Moon rises, on average, about 50 minutes later each successive day, and thus seems to 'fall behind' the Sun as the two celestial bodies make their daily journey across our sky.


The Waxing Crescent Moon, seen in the West in the evening hours, is called a 'young moon'. The thin crescent becomes readily visible about two to three days after New Moon and is visible for only a short while before the Sun sets. As the days pass, the crescent becomes more substantial; appears higher in the West after sunset each day – and consequently takes longer to set.

Note: you will not see a crescent moon rising in the evening sky! It will simply appear in the West as the sky darkens – and will set soon after the sun does.

2. The First Quarter Moon (approximately one week after New Moon) rises around noon and sets around midnight. It is at its highest point overhead at sunset. From around First Quarter through the Waxing Gibbous stage the Moon is often faintly visible in the afternoon sky.

The Waxing Gibbous moon hangs in the East at sunset, having risen a few hours before sunset. Each successive day it is closer to the eastern horizon at sunset as it works its way 'backwards' across the sky.

3. The Full Moon is opposite the Sun in our sky and so rises as the Sun sets and sets at dawn. Each day it rises nearly an hour later and appears higher above the western horizon at dawn.

The Waning Gibbous Moon rises from about 1-5 hours after sunset and is still up in the western sky when the Sun rises.

4. The Third Quarter Moon. occurs about three weeks after New Moon. This moon rises around midnight and sets around noon. It reaches its highest point in the sky around dawn. It can often be seen faintly in the day lit morning sky.

The Waning Crescent Moon is called the 'old moon' and rises in the East just ahead of the Sun. It is not visible for long before the sunrise brightens the sky too much to see it.


Seasons and Latitude
You know the summer sun rides high in the sky, while the winter sun rides low. But the moon's path across the sky will be the opposite – low in summer and high in winter.

Also, at higher Northern latitudes the sun, moon and planets will all cross the sky closer to the horizon and will rise and set further to the South than at lower latitudes. This will also make them appear to rise later and set earlier than at latitudes closer to the equator. (The effect is the same for the Southern Hemisphere; simply reverse the compass directions.)

Moonshine and Earthshine
During a few mornings or evenings of the crescent phase you may notice the dark portion of the moon's disc is faintly visible also. This ghostly effect is produced when the shadowed portion of the moon's Earth-facing side is indirectly illuminated by sunlight reflected from Earth's bright clouds.



Morning and Evening Star:
Venus, bright Eärendil, the Morning and Evening Star:

From Earth's perspective, Venus and Mercury don't behave like the other planets because their orbits are nearer to the Sun than Earth's is. For instance, some folks may not realize that you will never see the Evening Star rise! Actually, of course, it does rise – it just rises in the East in the morning a little while after the Sun does, so we can't see it in the bright sky. It follows the sun across the sky and then becomes visible shining brightly in the West as the sky fades. Similarly, Venus as the Morning Star rises before the sun; a brilliant jewel in the pre-dawn heavens; but is soon lost in the glare of the Sun's light. It precedes the Sun across the sky and sets before the Sun does.

As the Evening Star, Venus appears to lag behind the Sun and as the apparent distance between the Sun and the 2nd planet increases, it appears higher in our sky each evening at dusk. As Venus swings around the Sun day by day, it will climb well up into our western sky, then reverse its direction and sink lower each night until it disappears into the twilight glow at sunset. After some weeks it will reappear, rising just before the Sun in the mornings as the 'Morning Star' and repeat its dance of rising earlier each day and climbing higher in the morning sky, then reverse and sink lower each morning until it is again in line with the Sun. Mercury behaves the same way, but being both smaller and closer to the sun, it is more difficult to see, and is visible only briefly about 45 minutes after sunset or before sunrise when at its greatest elongation (right angles) from the Sun.



Solar Eclipses

Solar eclipses occur at the exact time of the New Moon. Because of a slight amount of wobble in the Moon's orbit, it is only a few times each year that the Moon is lined up directly enough with the Sun to completely or partially obscure the disc. However the phenomenon is visible only from a limited track on the earth's surface, and it can be many years between events in any specific location.

The Sun is about 400 times larger than the Moon – but it is also about 400 times further away. Depending on the exact distances between Earth and the Sun and between Earth and the Moon (due to orbital wobbles again) the Moon can appear large enough to cover all of the Sun's disc - a total eclipse; or small enough to leave a ring of the photosphere (the Sun's surface) visible – called an annular eclipse. When the Moon slides in front of the Sun, but is not centered on it and leaves a crescent shaped Sun visible throughout the event, it is called a partial eclipse. Partial eclipses are less rare for any given location than total eclipses, and can possibly occur more than once in a year. But it is not unusual for several years to pass between events.

Total eclipses are spectacular – that's why many people go to such incredible lengths to travel to a place where one can view totality. When the entire surface of the Sun is covered, the corona – the outer atmosphere of the Sun – becomes visible. It appears like gauzy white streamers radiating out from the black obscuring disc of the Moon.

The Moon is not visible except as it blocks the solar disc. The sky will darken during a total eclipse to twilight levels and bright stars and planets will appear. It often becomes noticeably cooler also. Any bright comets near the Sun may become visible too. Hazy stripes of light and shadow – called 'shadow bands' - can sometimes be seen on large light-colored surfaces.

During partial phases miniature images of the crescent Sun can appear on surfaces under leafy canopies – the leaves act to create 'pinhole camera' effects, and multiple images of the eclipsed Sun cover the ground beneath the trees. The Sun's light may appear 'weaker' and it may become a bit cooler even during the partial phases of a solar eclipse.

It is never safe to look directly at the Sun if even part of the photosphere (the bright surface of the Sun) is visible. Not even through layers of clouds. And certainly not through any device that focuses or magnifies the light. Severe eye damage or blindness can occur. Only during complete totality – when the corona is visible, is it safe to view it directly. Safe viewing techniques can be found here


Lunar Eclipses

Lunar eclipses occur at the time of Full Moon when the Moon's alignment with Earth allows it to pass through Earth's shadow. As Earth's shadow is much larger than the Moon's shadow, the event can be seen from a much larger portion of the Earth's surface than a solar eclipse. Lunar eclipses last longer and the shadow is less distinct than that of a solar eclipse.

During the total phase of a Lunar eclipse the Moon often takes on a reddish glow, as some light bends through Earth's atmosphere and the longer red wavelengths reach the Moon even in the depths of Earth's shadow.


Sky chart
This online sky chart is a handy reference for checking positions of celestial objects or constellations. Be sure to change the location and time features to match the approximate local and season/date of your story setting. Online sky chart



Additional helpful links:

Moon phase article and images
http://aa.usno.navy.mil/faq/docs/moon_phases.html

Dates of primary phases of the moon – tables
http://aa.usno.navy.mil/data/docs/MoonPhase.html


Sun/Moon rise and set data for any specific day & location
http://aa.usno.navy.mil/data/docs/RS_OneDay.html


Simple moon phase animation http://www.space.com/spacewatch/mystery_monday_030908.html


Full moon names (Harvest Moon, etc.)
http://www.space.com/spacewatch/full_moon_names_030214-1.html


This is a work of fan fiction, written because the author has an abiding love for the works of J R R Tolkien. The characters, settings, places, and languages used in this work are the property of the Tolkien Estate, Tolkien Enterprises, and possibly New Line Cinema, except for certain original characters who belong to the author of the said work. The author will not receive any money or other remuneration for presenting the work on this archive site. The work is the intellectual property of the author, is available solely for the enjoyment of Henneth Annûn Story Archive readers, and may not be copied or redistributed by any means without the explicit written consent of the author.

Story Information

Author: Ithildin

Status: General

Completion: Complete

Era: Other

Genre: Research Article

Rating: General

Last Updated: 01/17/12

Original Post: 04/17/04

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