Orienting the Night Sky

First Night's Stargazing

I'm hoping that now we're past midsummer's day, it won't be too long before I get chance to turn my recently rediscovered telescope towards the night sky.

I felt like I should get a refresher in some of the basics before I'm standing in the dark pointing my scope at random stars.​

So, I had a trawl of YouTube... and found:

Stargazing Basics!

David Fuller's aim in life is to promote dark skies for astronomy, and the upside of that is they've been producing useful guides for all astronomers to make use of.

Find the full video at the bottom of this post, but below are the 10 key facts from the video for me and any other 'almost ready to start' astronomers.​

1) Getting Oriented in the Sky Needs a System

To be able to find stars and other night sky objects in a world that is constantly moving about our heads and changing with the seasons, we need a system of navigation with its own language.

2) Start with Familiar Compass Directions 

Cardinal directions are our familiar north, east, south and west, and the points in between like north west and south east, that we use on the ground. To get started locating objects in the night sky, know where due north and south are.

Cardinal directions

Our familiar north, south, east and west

3) Split the Sky using the Meridian

The meridian is quite simply an imaginary line that splits the sky above your head in two and runs overhead from due south to due north on your horizon. This line is constant and does not move with the apparent motion of the stars.

Meridian on the night sky

The meridian splits the sky in two

4) The Zenith = the Point Directly Overhead

Using your meridian line, locate the point directly over your head; that is the zenith and, just like the meridian, it does not move relative to you.

Finding the zenith

5) Where to Find the Planets in the Sky

The line the sun appears to follow in the day is called the ecliptic. Because the solar system is in a plane, the moon and planets also sit on or very near to the ecliptic too.

Ecliptic - path of planets

The ecliptic is the path of the sun, moon and stars

As you know from experience, the ecliptic is higher in your sky in the summer than in the winter... just like the sun.

Ecliptic moved nearer the horizon

In the winter, the ecliptic is nearer the horizon than in summer

6) The Celestial Sphere

Imagine the sky you see above as the flat inside surface of a sphere surrounding the earth, this is the celestial sphere. It appears to move about our apparently static world.

the celestial sphere

The celestial sphere imagines the sky as the inside of globe around Earth

7) Fixing Points on the Celestial Sphere

Up until now, all of our lines and points have been set with reference to the earth and our location on it, now it's time to set some points that are static on the celestial sphere.

We start with the celestial north pole​ which is the point in the sky directly above (i.e. at the zenith of) Earth's north pole. This is marked for us (handily) by the polaris, the pole star. 

Celestial north pole

The celestial north pole is higher in the sky at northern latitudes

Further south, towards the equator, polaris is nearer to the northern horizon than it is when viewed closer to the north pole itself.

polaris from southern latitudes

... and lower in the sky at southern latitudes

Of course, there is a southern celestial pole as well for those of us in the southern hemisphere!

8) Projecting Longitude and Latitude

On Earth, lines around the globe (parallel to the equator) are called lines of latitude. Imaginary lines circling the globe the other way, i.e. from north to south poles, are called lines of longitude.

Now, imagine projecting them onto the celestial sphere as it appears to surround the Earth and you create lines of declination and right ascension.

the celestial sphere

Direction of the lines of declination and right ascension on the celestial sphere

9) Right Ascension

Face north and imagine the sun rising from the east. You are now thinking about the sun ascending on your right, and have painted for yourself a line of right ascension.

These are the lines on the celestial sphere that connect the celestial north and south poles. They start at zero in the constellation of Aries the Ram and are split in intervals of hours and minutes. 

Lines of right ascension

Showing lines of right ascension on the celestial sphere

10) Declination

Equivalent to Earth's lines of latitude, the longest line of declination draws the celestial equator, and all the other lines of declination run parallel to it, measured in degrees. The celestial equator is 0 degrees, and the celestial poles are at right angles to that, so 90 degrees north and south.

Lines of declination

Showing lines of declination on the celestial sphere

Recap

I've now learned the (very) basics of orienting myself in the night sky and look forward to using it with my star charts.

Here's a recap of what I took away:

  1. Cardinal directions: north, south, east and west down here on Earth
  2. Meridian: The imaginary line that joins north to south and splits the sky in two
  3. Zenith: the point on the meridian directly over your head
  4. Ecliptic: the path traced by the sun and (approximately) the moon and planets
  5. Celestial sphere: the sky imagined as the inner surface of a sphere around Earth
  6. Celestial poles: the zenith of an observer stood at Earth's north or south pole
  7. Declination: lines of 'latitude' parallel to the celestial equator at zero degrees
  8. Right ascension: lines of longitude joining the north and south celestial poles

What you can take away is a free, detailed infographic, beautifully designed to bring these points to life and make them easy to print off and refer to in the future.

Click on the picture to access your full, detailed infographic.


Orienting the Night Sky - the Video

It would be great to hear how you learned your way around the night sky. Leave a note in the comments box and I'll be sure to respond.

In the meantime, check out the full video below:​

Stargazing Basics - Full Video