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6 Naked-Eye Astronomical Concepts


I am a marketing professional holding a postgraduate degree in management. Astronomy is my hobby.

Milky way galaxy stars appear fixed in relation to each other but the planets move

Milky way galaxy stars appear fixed in relation to each other but the planets move

The term "observational astronomy" is self explanatory. It talks about the things we can learn about space and universe by mere observation of night sky. It includes all we can see with our own eyes or through a telescope. I would limit the discussions only to naked-eye observations in this article.

We could confirm several scientific principles by mere observation of the night sky. Some of these may be basic, but understanding the elementary concepts is the first step before taking a deeper dive into the advanced ones.

Astronomical Concepts to Appreciate With Naked-Eye Observations

  1. Differentiating planets from stars
  2. Sun's position in the sky influences Earth's seasons
  3. Moon is lit by the Sun.
  4. Moon is closer to Earth than Sun is.
  5. Moon causes the ocean's tides.
  6. Venus and Mercury are in inferior orbits

1. Differentiating Planets From Stars

When we travel in a train, the nearer objects would appear to move out of sight faster than the farther objects. Almost all the stars are so far away they would appear stationary in relation to each other. But planets change their position against the background stars every night since they are closer to us and they all go around the sun albeit in different orbits.

To begin with, one should learn to identify the major constellations like Orion, Big dipper or Pegasus. This is the critical first step in becoming familiar with the night sky. Then one should check if the relative positions of nearby stars change in relation to constellations after a few days.

The ones that change their positions against the background stars should be the planets. We know that the orbits of all the solar system planets form the shape of a disc around the Sun. The disc shape of the orbits has relevance in planet hunting because the planets follow the same path taken by Sun from east to west. We also call this path the ecliptic.

Mercury, Venus, Mars, Jupiter and Saturn are the five planets visible to the naked eye and so we call them the naked-eye planets. One needs a powerful telescope to spot the other two planets, Neptune and Uranus.

Maximum Brightness of Visible Planets

PlanetsApparent Magnitude











2. Sun's Position in the Sky Influences Earth's Seasons

Sun does not rise or set in the same direction. There is a gradual shift in Sun's position through the year. In reality, it is not the Sun that is shifting its position but it is the axis of Earth's rotation that keeps tilting. The equatorial region faces the Sun on most occasions.

The northern hemisphere gets heated more when the axis of rotation tilts northward. Because of the tilt in the axis, northern and southern hemispheres get heated in varying measures. The differential heating results in a corresponding differential pressure leading to wind formation. It causes the winds to flow through the oceans and carry moisture to the land.

The ensuing monsoon rains are the lifeline for many life forms including our own human race. Thus, we see how the cosmos can influence things on Earth. Northern Hemisphere has summer months from June to August when the Sun appears to be overhead. The Sun seems to shift southward in the winter months from December to February. One can confirm the same by looking at the shadow cast by Sun that changes its direction between summer and winter months.

3. Moon is Lit by the Sun

We all know that the Moon is lit by the Sun. We can confirm the same by our own observation with the naked eye. Let us watch moon on a night, when it is a crescent. Both the lit and the unlit side of the crescent moon would be visible.

The lit side will always face the sun. This is a part confirmation that Moon is lit by the Sun. We can also observe the full moon that would rise when the Sun would be setting. This means that the Sun and Moon are on two sides of our planet. Thus, we get to see the round lit face of Moon only on a full moon day when the Sun and Moon are on either side of Earth.

We can get the final proof by observing the Sun and Moon on the new moon day. Some of us would not have seen a new Moon in our lives as the new Moon is visible as a dark grey circle in day time closer to Sun. It is unsafe looking at the Sun as the Sunrays have a blinding effect. We can block the Sun from our view by placing our hand in front before locating the New Moon. Once we locate the New Moon closer to the Sun, we could conclude that we are looking at the unlit side of moon. The lit side should be on the other side facing the Sun.

4. Moon is Closer to Earth Than Sun is

We can find the proof for this during a solar eclipse. It is not advisable to stare straight at the Sun on any day. So please take enough precautions such as using a solar filter to look at the eclipse.

One can also consider options like a pinhole projector or a mirror projector. We can make both at home as a DIY project. Solar filter is a safe way to view the solar eclipse. It is not safe to look at Sun anytime and not just during eclipse alone, as some might think. Looking straight at Sun could cause serious damage to the vision.

One can see the disk of the Moon coming in front of the Sun and block the light from reaching Earth during the solar eclipse. So if Moon can block sunlight from reaching us, it should be at a shorter distance compared to Sun.

Waters receding from the Ruby Beach during low tide

Waters receding from the Ruby Beach during low tide

5. Moon Causes the Ocean's Tides

High tide always occurs when Moon is right overhead or underneath. Low tide happens when Moon is near the eastern or western horizon. This explains how the gravitational pull of the Moon causes the ocean's tides.

The high and low tides become more pronounced during New Moon or Full Moon days. This is because Sun's gravitational pull also has an influence on tides, though Moon has a more decisive effect on tides. During a full moon or new moon, Sun, Earth, and Moon are all aligned in a straight line. The gravitational force of Sun and Moon adds up to make the tides more pronounced.

One can observe the tidal movements by visiting a nearby beach and making periodic observations at a gap of 3 hours. One would then understand the link between Moon's position and the height of the tides.

6. Venus and Mercury Are in Inferior Orbits

Venus and Mercury are two planets found closer to where Sun is. Venus is visible as an evening star or morning star just for a few hours after sunset or before sunrise. We would always find Mercury closer to the sun. It is visible for around half an hour after sunset or before sunrise.

We cannot see both the planets in the night sky after 10 PM or before 3 AM. So from our line of vision, these planets always lie somewhere closer to Sun. Such a scenario is possible only for inferior planets with orbits closer to Sun than ours.

Please let me know if you have observed proofs for any other astronomical concepts.

Please share your comments.

lesliesinclair on January 20, 2014:

Night sky gazing is a treasured time for those who can see the stars, typically outside urban areas.

Mohan Babu (author) from Chennai, India on January 02, 2014:

@lyttlehalfpint: Thank you so much for your comments.

lyttlehalfpint from Canada on December 31, 2013:

Complicated subject made understandable, great lens!

Mohan Babu (author) from Chennai, India on December 30, 2013:

@sukkran trichy: Thank you so much for your comments.

sukkran trichy from Trichy/Tamil Nadu on December 30, 2013:

my favorite subject. thanks for sharing some interesting information.

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