Nick Tsagaris - ISS Is Passing Over Australia, Here's What You Need To Know To Spot It

Australians sure are a curious bunch when it comes to the International Space Station (ISS).

We're one of the top countries in the world to seek out where and when we'll next see it floating by in the night sky, according to NASA.

This weekend's a great opportunity to get out for a squiz — if you're in or around Brisbane, Sydney, Melbourne or Perth, you're in for a treat.

Want to get in on the fun? It's easy. Here's what you need to know:

ELI5, what is the ISS?

ISS is jointly owned by the United States, Russia, Canada, Europe and Japan.

It's been orbiting the Earth since 1998, and has been slowly expanded over the years.

The best way to describe it is "Earth's space lab", astrophysicist Dr Brad Tucker says.

"If you want to test things in space, if you want to put things in space, you need to build an entire satellite. Or the space station really was this multi-national effort to provide that lab to do experiments," Dr Tucker said.

"Lots of groups mount telescopes or measuring devices around the space station so instead of building all these individual satellites you can put it on the space station.

"You also have an astronaut there so if something goes wrong they can work on it, send you data, or fix it. So it really is a space lab."

ISS has at least another 10 years of use left in it, and Donald Trump is interested in selling the US stake in it.

There are currently six crew members on board.

How many times a day does ISS orbit the Earth?

Quite a lot.

Every orbit is about 90 minutes, so two orbits every three hours, or 16 per day.

That's a whole lot of sunrises and sunsets for those on board.

It's not like ISS is following any set path either — the station crosses all parts of the Earth because the orbit "wobbles".

"But a lot of those times are during the day time, or it passes just on the horizon, but because it's doing it so often there's actually a number of times the space station passes overhead," Dr Tucker said.

"Usually in a given week or so you can find a time that the space station is passing over in the evening over an area near you."

How will I know when the ISS is flying overhead?

NASA has its own "Spot the Station" website set up where you can check sighting opportunities from nearly 100 locations across Australia up to 10 days in advance.

You can sign up there for text message or email notifications whenever there's going to be a decent chance of spotting the station.

Generally you should get an alert 12 hours ahead of a scheduled sighting.

There are also some apps for your phone you can set up for similar alerts.

ISS Detector is one, ISS Spotter is another.

How often can I expect to see the ISS?

Some places around the world are luckier than others when it comes to ISS sightings.

Some spots can get only one sighting a month, others can get several a week.

The planets really have to align (space pun intended) if you're going to see the ISS doing its thing in low orbit.

You need the correct:

• Time: It needs to be dark where you are. It has to be just before sunrise or just after sunset.
• Location: Just like real estate, it's all about "location, location, location". The station must be 40 degrees or more above the horizon from where you are for it to be visible.
• Weather: Clear skies are best obviously, cloudy conditions can ruin your chances of a sighting.

Tick all three boxes, and you're in with a shot!

The ISS is due to fly over my area. What am I looking for?

A very bright light moving across the sky — somewhere between an aeroplane and a shooting star.

"The space station is the brightest moving object in the sky, and it will move quickly across the sky," Dr Tucker said.

"It moves faster than an aeroplane, but the lights don't blink, but it's like a shooting star where it's just this bright light that moves.

"It can last from 20 seconds up to a few minutes depending on where it's orbiting."

No need for a telescope either — you can spot the ISS with the naked eye.

Basically it'll look a little something like it does in this video:

I've just got an alert about an upcoming sighting of the ISS. How do I decipher the information?

If you sign up to one of those apps mentioned above, you may get a notification like this:

SpotTheStation! Time: Wed Apr 25 7:45 PM, Visible: 4 min, Max Height: 66 degrees, Appears: WSW, Disappears NE.

To break it down for you:

Time: When the sighting opportunity will begin in your local time zone. All sightings will occur within a few hours before or after sunrise or sunset. This is the optimum viewing period as the sun reflects off the space station and contrasts against the darker sky.

Visible: The maximum time period the space station is visible before crossing back below the horizon.

Max Height: It represents the height of the space station from the horizon in the night sky. The horizon is at zero degrees, and directly overhead is ninety degrees. If you hold your fist at arm's length and place your fist resting on the horizon, the top will be about 10 degrees. It's measured in degrees (also known as elevation).

Appears: The location in the sky where the station will be visible first. This value, like maximum height, also is measured in degrees from the horizon. The letters represent compass directions.

Disappears: Represents where in the night sky the ISS will leave your field of view.

So for the instance above, the ISS will be visible at 7:45pm for four minutes. It will appear 66 degrees above the horizon from west south-west of your position, and disappear in the north-east.

Is there anything else I can spot orbiting the Earth?

Yes, other satellites!

"I would say on any given clear night if you're looking at the sky you'll see one satellite every 30 minutes to hour," Dr Tucker said.

One thing to keep an eye out for are iridium communication satellites and their iridium flares.

"The panels are really reflective, so there won't be a bright streak like the ISS but there will be a bright flash," Dr Tucker said.

"So sometimes if you see a bright flash it's actually what we call an iridium flare, and if the angles are right you get a bright reflection off these communication satellites."

Here's what it looks like:

By: abc.net.au