Visible Planets

One evening  a few weeks ago – more than a few now, Kam pointed to the sky.  I didn’t know what we were looking at.  Look to the left of the moon mum, there’s a planet.

Oh ok, how do you know that?  Mum, because it’s big, it’s bright, it’s not so sparkly, like you and grandad tell me. Oh, ok.

So, being the expert, I look on the iPad.  Sure enough I scan the area, and oh my, it’s a planet.  It’s Jupiter.  Oh golly gosh.

Visible Planets

Jupiter and Earth's Moon
Jupiter and Earth’s  moon:NASA

Mercury, Venus, Mars, Jupiter and Saturn are the brightest planets in the sky.

We can see them with our eyes, indeed they are known as the Naked Eye Planets.  Of course, you must know where and what to look for – pretty amazing we think.

The planets are visible for most of the year, except when they are close to or in the Sun’s glare.  They are not usually all visible in the sky at the same time.

Planet or Star?

You can tell the difference between a planet and star.

Planets

image
Mars, Jupiter, Mercury, Venus, Jupiter

A planet’s position changes slightly against the stars from one night to the next.  Their brightness varies in a regular cycle (pattern) over time.

Planets do not produce their own light;  their shine is sunlight reflected into space, some of which we see from Earth.

The proportion of reflected sunlight  (albedo) depends upon:

  • the planet’s size,
  • the amount of cloud cover it has and
  • how reflective the planet surface is.

How bright a planet appears when we look at it depends upon:

  • its distance from the Sun,
  • its apparent size and
  • the relative positions of the planet and the Earth in their orbits.

Stars

Stars are so far away from Earth that they look like a dot of light in the night sky.  They seem to twinkle (scintillate) because of turbulence in the Earth’s atmosphere.

Even looking through the largest telescopes, a star looks little more than a pin point of light.  Stars generate their own light by having internal nuclear fusion reactions.

Naked Eye Planets

image
Mercury & Venus above Earth’s Moon.

The naked eye planets, are close enough to Earth to form a disk (circle) in the night sky.  When they are well above the horizon, the planets shine with a more steady, less twinkly, light than the stars.

Saturn and Mars could be mistaken for stars – but only during their dimmer periods when they are further away from Earth.  Often the planets are best seen in the early morning or early evening.

Planet Visibility

The length of time a planet (or other celestial body) is visible from Earth is known as an apparition.

An apparition begins when a planet emerges from the Sun’s glare and ends when it disappears back into the glare of the Sun.

For Mercury and Venus, this is during either the morning sky or the evening sky.   For Mars and planets further away than Mars, this is when the planet becomes visible in the dawn sky until it disappears into the dusk sky.

The length of a planet’s apparition depends upon:

  • how long it takes the planet to orbit the sun (orbital period) and
  • the orbital positions of the planet and the Earth with respect to the Sun on a given night.

Apparitions can last a few weeks – Mercury, to nearly two years – Mars .  A planet is normally seen at its best for only a part of this time.

A Note to You and Me

We enjoy looking for planets.  We written two posts about what to look for. We started this in April and have just added new posts for May.  The links for these posts are:

Visible Planets May 2015 – Mercury and Venus and
Visible Planets May 2015 – Mars, Jupiter and Saturn

Thank you for reading this post, we hope you have found it interesting. If you like it, please like it, it gives Kam a smile. X

If you can expand on it, let us know, we’d be really grateful.

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2 thoughts on “Visible Planets

  1. Kamtime April 20, 2015 / 20:44

    ELouise, thanks for saying hello. There is going to be a happy little boy tomorrow. Funnily enough Kam has a set of toy binoculars, (which are surprisingly good), he’s have them out in earnest tomorrow evening. X

    Like

  2. Elouise April 20, 2015 / 20:15

    Yup! Mum was right! I love looking at the night sky–with and without my birding binoculars!
    Elouise

    Like

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