GPS uses Quasars

GPS uses Quasars to work

GPS uses quasars to get its own position
GPS satellite in low Earth orbit. Credit: NASA artist’s impression
The Global Positioning System (GPS) is precise.

That precision originates in a mind-blowing place!

GPS signals tell billions of people where they are each day.

GPS helps pilots land planes and captains steer ships.

GPS signals stamp locations onto millions of photos.

GPS gives you driving directions.

But, where does GPS get its own GPS?

The GPS for GPS

How does GPS know where a GPS satellite is?Click here to continue reading…

Astronomy Koan

Astronomy Koan – Definition

A family views the visible orbit path of the earth.
A family views the visible orbit path of the earth.

An astronomy koan is a short, easy-to-memorize phrase that distills a key teaching about astronomy (especially physical astronomy).

The words are simple enough for a child to learn, but they carry complex insights about scientific observations.

The astronomy koan is a mnemonic that has layers of meaning or presents an ambiguous or challenging observation in a pithy phrase.

Try memorizing one of these – you can bring these with you everywhere.

Four Physical Astronomy Koans


That star rose earlier today.

The moon moves toward the dawn.

Night is where you are.

Same Sun all night. Dusk to the left, dawn to the right.


What do you think about these?

Do you know any astronomy koans?

Share your ideas in the comments section.

Stellarium – Find the Humanity Star

A new satellite called the Humanity Star looks like a disco ball

Update Apr. 1, 2018.

The Humanity Star is no longer an active satellite – it has fallen out of the sky: https://www.theverge.com/2018/3/22/17144208/rocket-lab-humanity-star-satellite-new-zealand-astronomy

However, even though the Humanity Star is now gone, this article still teaches you how to load satellites into Stellarium. So, read on for a quick tutorial on how to track any satellite in Stellarium.

Looking for information on how to track the Humanity Star any satellite location using Stellarium astronomy software?

Here is a quick tutorial on how to find the Humanity Star any satellite using Stellarium.

You can track the position of the Humanity Star with Stellarium
The Humanity Star satellite before launch – still on the Earth.

Rocket Lab founder and CEO Peter Beck announced that the company’s rocket had placed a special satellite in a 90 minute orbit around the Earth.

A lot of people want to see this new “star” in the sky. Stellarium can help you do that.

If you don’t have Stellarium, you can download a copy here. And I have a few tutorials that can help you get started with this amazing piece of software.Click here to continue reading…

Quiz – Can we see the Sun at midnight? Where is the Sun?

Can we see the Sun at midnight?

Yes. We can see the Sun at midnight. But, only if we are at one of the polar regions during the Summer season.

Image of the Sun's rays hitting the Earth. The Earth is tilted 23.4 degrees. Summer is when the northern hemisphere is titled toward the Sun. The summer Sun never sets - not even at midnight - if you are north of the Arctic Circle.
You can see the Sun at midnight! If you are at the North Pole in summer.

A quiz – seeing the Sun at midnight – don’t scroll til you try to answer!

When you see the Sun “rising” in the morning at dawn you are facing the east.

When you see the Sun “setting” at the end of the day you are facing the west.

Assuming you are not above the Arctic circle and not too close to the equator… if you could look right at the Sun (when the night is exactly half over) – by looking through the Earth – which cardinal direction would you be facing? East, West, North, or South?

Looking north or south to see the Sun at midnight?
A compass rose showing the cardinal directions.

Click here to continue reading…

See Mercury and Venus orbits during the day

Your hands and arms help you see the orbits of Mercury and Venus and the shape of solar system

Question: If you could see the orbit of Venus would it fill the whole sky?

The answer might surprise you!

You can use your hands and arms to see the size of the orbits of the solar system’s inner planets: Mercury and Venus.

Imagine (as pictured below) if the orbit of Mercury were visible as a red oval and the orbit of Venus were visible in green.

Use your hands and elbows to see Mercury and Venus orbits any time of day or night. The orbits of Mercury and Venus can be seen.
Two hand spans show Mercury’s orbit, elbows show Venus’s orbit.

Physical Astronomy – see Mercury and Venus orbits

Caution! Do not look directly at the Sun without proper solar safety glasses on.

Turn toward the Sun, hold your arms out straight, hands up in the air with fingers spread wide and thumbs touching. Your pinky fingers now span the width of the orbit of Mercury and your elbows span the width of the orbit of Venus.

Both of the entire orbits of Mercury and Venus orbits would be visible in the sky all at once – if they could be made visible during the day.

Click here to continue reading…

Shapes with Shadows – astrosketching Moon features with Alex Massey

Shapes with Shadows – what they can tell us

This the first of two special guest posts by Australian astrosketch artist Alexander Massey 

Live View Sketch of Moon craters Azrachel, Alphonsus, and Ptolemaeus by Alex Massey

Ptolemaeus, Alphonsus, and Arzachel… the names of three massive, interlocking craters on the Moon. These three craters tell the story of the ancient Moon’s creation and evolution. It’s a story of violent bombardments and oceans of lava. We can use light and shadows to reveal the shapes and deep history of these features.

Most people think of astronomy a science of light. But, light creates shadows when it hits things. Those features that lie in the shadows, the dark parts and seemingly just-in-the-way-of-the-light parts, are just as important as those that shine brightly. These dark shadows form most of the mass of all galaxies, house stellar nurseries, reveal old lava rivers on the Moon, and create curious plays of light and dark. These can play tricks on our eyes and make patterns appear.

Click here to continue reading…

Walk to Mintaka

Physical Astronomy by Daniel Cummings
Mistakable rises toward the zenith as you walk toward the equator
As you walk toward the equator, Mintaka appears to rise higher in the sky.

In this post we will learn how to use one bright star of Orion’s belt to visualize the Earth’s equator.

Mintaka is a Star in Orion’s Belt

When you look up at the winter sky in the northern hemisphere, Orion and his famous belt are impossible to miss. The belt is made up of three stars of equal brightness.

One of these stars is called Mintaka and it is a guidepost for finding the Earth’s equator in space. Click here to continue reading…

Arms around the ecliptic

Learn to see the ecliptic

Physical Astronomy by Daniel Cummings

Ecliptic Arms

The sun follows the same path through the sky every day.

Sun up. Noon. Sun down.

The sun starts the day in the east in the morning, rises high in the sky at noon, and settles down again in the west for a nap at night.

See the ecliptic

Here is an exercise to discover that path – the ecliptic.

Click here to continue reading…

Groundhog Day Shadow Tracker

Physical Astronomy Tool by Daniel Cummings

Groundhog Day Shadow Tracker Lesson Plan
It’s Groundhog Day!

What better way to celebrate Groundhog Day than to Build your own Groundhog Day Shadow Tracker

Let’s do some Physical Astronomy. The experience will help you to understand the movement of the earth and sun through the seasons. You will build a scientific instrument that is also a fun garden decoration and you will be able to track the Groundhog’s Shadow all Spring!

Click here to continue reading…

A new star will appear in the sky in 2022

Binary star merge to form a new star - a star in a starAn amazing thing is about to happen! A Star in a Star will be born.

You  can witness the birth of a new star in the night sky.  The new Star already has a birthday: 2022!

According to scientists, the new star will form when two stars that are orbiting each other grow so close that they merge into one.

The new star will appear in the constellation Cygnus. You can see the approximate location marked by a red circle in the Stellarium screenshot here:

A screenshot of Stellarium showing the new star location under the constellation Cygnus's left wing

The image of the two blue stars on the home page of this Star in a Star site shows what scientists think it looks like now. This impressive video shows an artist’s rendering of the star merge.

In the pair, one star is larger than the other so in the end, there will be a new star…  A Star in a Star.

The Moon Dance – Learn Moon Phases

PHYSICAL ASTRONOMY BY DANIEL CUMMINGS

The moon dance helps you learn and understand the phases of the moonAt sunset.

Face the sun.

Point your right hand toward the Sun.

Now point your left hand toward the Sun.

Both hands should be pointing at the sun.

Now, turn a little bit to the left, keeping both hands pointing at the sun.

Swing your left arm out until it is pointing in the opposite direction from the sunset. Bring your hands together again and repeat this swinging motion.

Bring your hands together again and point them both at the sun. This time, instead of swinging, bounce your left hand, leftward, some number of times… (14 is perfect if you can do it) …until it is pointing in the completely opposite direction from the Sun at sunset. Your left hand should now be pointing East.

Was the moon at any one of those 14 hand bounce spots? That is the age of the moon in days.

Please post your questions in the comments!