Observing Space

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What can we observe in tonight's sky?

We are able to see many objects in space with our own eyes. They might appear brighter to us if they are larger, or closer, or give off a lot of light.

When the Sun is not visible in our sky, its light no longer bounces around in the atmosphere, and so we can see through the air to the rest of space.

The brightness of an object we see depends on how much light comes out from it and how close it is to us. All of the stars we can see are stars in our own galaxy. The moon and planets are brighter because they are closer to us than the stars.

In Aotearoa, we are always able to see the Southern Cross and the Pointer Stars on any clear night of the year. To find it, you need to:

Face south and then look for this pattern of stars in the sky
The two brighter stars are called the "pointer stars" because if you draw a line with them, they'll point to the Southern Cross.
Depending on the date and time of the night, the Southern Cross may not always be upright like in the image to the right. It may be on its side or even upside-down!

Activity: Stellarium-Web

Use the interactive below or click on this link: https://stellarium-web.org

Change the date at the bottom right of the page to see what we will be able to see in the sky tonight (assuming it is a cloudless night).
Will we be able to see...
- - the Southern Cross?
  - the Milky Way galaxy?
  - the Moon?
  - other planets?
How will these things change over the course of the evening?

The Southern Cross and two Pointer Stars belong to the Centaurus constellation.

Let's take a look at what other information Stellarium can give us:

Find Alpha Centauri and click on it.
How far away is Alpha Centauri?
What do you think it means when it says this is a "triple star"?
Find Hadar (Beta Centauri) and click on it.
How far away is Hadar?
How much farther awa is Hadar compared to Alpha Centauri?

Alpha Centauri

A triple star system in the Centaurus constellation because it is made up of three stars:
- - Alpha Centauri A (Rigil Kentaurus)
  - Alpha Centauri B (Toliman)
  - Proxima Centauri.
Proxima Centauri is the closest star to our solar system
The Alpha Centauri system is the closest star system to the Sun, located about 4.37 light-years away.
The faintest of the three stars in Alpha Centauri, Proxima Centauri, is the closest star to the Sun, at 4.25 light-years.
Proxima Centauri is a small, dim red dwarf star, much smaller and fainter than our Sun.

Hadar (a.k.a. Beta Centauri)

Hadar is the second brightest star in the Centaurus constellation, after Alpha Centauri.
It is a blue-white supergiant, much brighter and larger than our Sun.
Hadar is also a triple star system.
- - Hadar Aa
  - Hadar Ab
  - Hadar B

How can we find North and South?

There are two ways we can use the Southern Cross to find south.

Run an imaginary line down the long axis of the Southern Cross and extend this line 4.5 times down to the horizon – that's south.
The South Celestial Pole is where a line from the mid-Pointers (at a right angle) meets the Cross's long axis. Drop down for south.

Polynesian Navigation

Polynesian navigators used star charts as one of their knowledge systems for navigation. A star chart is a mental construct made from observation and memorisation of stars and how they move across the night sky.

In the open ocean and on cloudless nights, polynesian navigators (from the Hawaiian example) can determine East and West by how specific stars (memorised in their star chart) move. They knew that stars move from East to West. They can determine South by using the Southern Cross (4 lengths extrapolated then straight down to the horizon = south), and if they are in the Northern Hemisphere, they can determine North by using the North Star.

More on Observing Space

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