Proper Motion Simulator

by Tony Dunn
Over a person's lifetime, the constellations don't appear to change. But over millenia, they noticably change.
The Proper Motion Simulator allows you to see the stars as they were in the distant past, or will be in the distant future.
It also allows you to take a journey on an imaginary spacecraft through the constellations.

You can even watch in 3d!

This program runs completely within your HTML5 compatible browser. There is nothing to install. You will not be bothered with messages telling you to update your Flash or your Java. It will run on Windows, Mac, iPads, smartphones, Kindle, or anything with a web browser.

Barnard's StarBarnard's Star has the fastest proper motion of any star in the sky
PrecessionEarth's celestial pole doesn't always point to Polarius. It has a 26,000 year cycle. Sometimes Vega is the north star.
Precession Down UnderThe southern hemisphere doesn't have a bright pole star. But that hasn't always been the case. And it won't be the case in the future. Watch as Sirius migrates south and becomes the pole star in the year 67,000, and again in the year 154,000.
Journey to OrionTravel to and through the constellation Orion.
Orion's proper motionWatch as Orion's shape changes over time
Pleiades proper motionWatch as the Pleiades shape changes with time
Journey to the PleiadesTravel to and through the Pleiades
Taurus proper motionWatch as Taurus the Bull changes shape over time. The most prominent star, Aldebaran doesn't share proper motion with its neighboring stars.
Alpha Centauri proper motionThe closest star system to the Sun is the Alpha Centauri system. This triple star system consists of two bright stars that are close together and appear as 1 star (Rigil Kentaurus) in this simulation. The thrid star, Proxima Centauri is the closest star to the Sun, but too dim to see with the naked eye. Watch as their high proper motion cause them to race across the sky towards the Southern Cross.
Big Dipper proper motionWatch as the Big Dipper changes shape over time.
Endless TourEnjoy the view as you travel in a giant circle of radius 400 light years, centered on the Sun. Pass through the heart of the Pleiades with each lap.
Big Dipper in 3d Cross your eyes to form a single image with a baseline of 4 light years to see the stars jump out at you in this 3d view.
YouTube of the Big Dipper's proper motionIn case your computer has trouble running the simulations, you can watch it on YouTube
YouTube of the Journey to OrionIn case your computer has trouble running the simulations, you can watch it on YouTube

Keyboard shortcuts

MShow / Hide controls
HShow / Hide Hipparcos IDs of stars
LShow / Hide proper names of stars
PPause / Play
RForward / Backwards Time
QGenerate a link to the current state of the simulation


The button in the top-right corner [<...] hides all the other controls so you can see more stars.

Below this button are three more buttons: [>], [<-], [Epoch 2000].
[>] is the Play / Pause button. Your simulation begins paused. Press to begin.

[<-] is the time direction button. Press to make time go backwards and see the constellations in the past. Press again to make time go forwards.

[Epoch 2000] returns you to present day.

Below this is a slider control surrounded by a [-] button and a [+] button. Use these to move immediately into the past or future.

Next comes the simulation speed slider and buttons. Use them to speed up or slow down the simulation.

Your imaginary space ship is initially in the solar system, allowing you to see the constellations as viewed from Earth.
Give your ship some speed, and it will take you on a journey through your favorite constellation.

Star brightness is an arbitrary number between 0 and 200. Use it to adjust the brightness of the stars.

You can also adjust the minimum and maximum size of stars by editing these numbers.

If you want to see Proxima Centauri as it moves through the sky just below Alpha Centauri, you may need to increase the minimum star size.

The Zoom slider and buttons allows you to see more or less sky.

The dropdown list contains all 88 constellations as well as many common asterisms and notable stars.
Choose an item from this list to center it on your screen. Give your ship some speed and journey to that constellation.

You can also manually edit the RA and Dec fields to point to any position in the sky. Just adjust the numbers and press [Go].

You can turn on the Asterism lines to make the constellations look more familiar to you. Check "Names" to see the names of the constellations.

If you want to see the official constellation boundaries, check "Boundaries".

A Right Ascension and Declination grid will appear if you select "Grid". You can change the spacing of the grid lines.

Selecting Stereo allows you to view the sky in 3d. When you choose this, other options become visible.
You can adjust the baseline, which is the distance between your two "eyes". It is set at 1 AU as default. You can manually edit this number to anything you like.
Be careful not to make the baseline too large. Between 1 and 4 LY is usually ideal. Set it to 0.01 to watch nearby stars like Alpha Centauri and Proxima Centauri.

It also allows you to view either "Parallel" or "Cross-eye". This simply switches the two images.

The final controls are "Proper" and and "Hipparcos". Selecting these will identify the stars on the screen with either their proper name or their Hipparcos ID.

Fun Stuff To Try

Select the Big Dipper and press Play [>]. Watch how it changes over a period of thousands of years. Press the Time Backwards button [<-] and view it as ancient civilization saw it.

Select Orion. Orion is distant and changes very slowly. But the foreground stars move like a swarm of bees.
Select "Stereo" and change the baseline to 3 LY to get a feel for the depth of this constellation.
Give your spaceship some speed and travel to Orion. Watch the Pleiades change shape as you pass them.

Select Pleiades, give your spaceship some speed and fly through them.

Select Alpha Centauri. Increase the minimum star size to 0.5 and slide the brightness slider to maximum, and watch as Alpha Centauri (also known as Rigel Kentaurus) and Proxima Centauri move together against the background stars.
Select "Stereo", and change the baseline to 0.2 LY to witness them as truly "foreground" stars.

Select Barnard's Star. Watch how fast it moves against the background.

About the Star Catalog

I'd like to acknowledge David Nash of This program uses a subset of his HYG 3 catalog. It includes nearly 18,000 stars. This is all stars brighter than magnitude 7. Additionally select stars with high proper motion, and any star that has a proper name is included. I'd include all 100,000+ stars from his catalog, but it makes my computer run too slow!


Tony Dunn

Follow @tony873004

To discuss this simulator, visit my forum at Suggestions, bugs, interesting uses and all comments are welcome. Forum