Celestial Globe

This celestial globe will help you understand the motion of stars and the Sun as we see it. It also allows you to determine a lot of astronomical parameters such as: times of sunrise/sunset, rising/setting times and directions of stars, anywhere anytime. Predict visible constellations above your head, duration of twilight, period of visibility of constellations...

A sky chart is printed and cut in 12 globe gores, which are then glued on a polystyrene sphere to make a celestial sphere. The stand is laser-cut on plywood.

Important note: most celestial globes available in stores nowadays display the constellations as we see them in the night sky. It makes sense if the purpose is to learn to recognize them, although it's inconsistent with the star's motion around us. A 'true' celestial globe represents the constellations as seen "from outside" the celestial sphere, hence they're printed reversed sideways.

1. scissors
2. printer
3. 3 sheets of paper
4. 1 wooden skewer (24cm, 3mm)
5. 1 polystyrene sphere (diameter 18cm) made of 2 hemispheres
6. 4 small hex nuts
7. all-purpose glue
8. wood glue
9. access to a laser-cutting machine
10. 6mm diameter wood rod (length about 1m15)
11. 2 wooden dowels (6mm diameter, length about 1cm)
12. a hacksaw (to cut wood rods)
13. a 50cm x 37 cm plywood board (thickness 5mm)

Print this PDF document without scaling up or down (100% scale). This document is fit for a 18cm diameter sphere.

The polystyrene is a set of 2 hemispheres. They join at the celestial equator. The wooden skewer will be the axis of the celestial sphere.

Punch 2 holes at the center of each hemisphere and pass the skewer through. Join the hemispheres.

With a pencil draw small marks on the equator, evenly spaced by 4.7cm. This will help glue the 12 gores evenly around the sphere.

To put the sphere on a table, you'll need a bowl of appropriate diameter.

Cut the 12 gores and trim their points (about 2mm each end).

Glue them one by one on the sphere. Each gore is labeled ('1h', '3h', ..., up to '23h') on its equator line. These numbers have to be set from left to right around the sphere. The constellation drawings will join from one gore to the next.

Put glue only along the largest symmetry axis of each gore, since their edges won't be glued to the sphere.

For a better result, carefully align the equator line of each gore to the junction of the 2 hemispheres, and make sure they point at the poles (skewer).

Use the marks you made on the sphere to set the gore evenly around the sphere.

Depending on the laser cutting machine you use, a .svg file or a .dxf file will be needed.

The files were made for 5mm plywood.

The disc is the base of the stand. The 3 concave pieces are glued together (the smaller on between the other two) so they form a cradle for the meridian. Align their holes and pass a wooden dowel through each hole.

Then glue the 2 feet at each end of this cradle, and glue the 2 feet inside the 2 notches in the middle of the disc.

The upper side of the horizon has to be exactly 13cm from the upper side of the disc. Cut 8 wooden rods 13.5cm long. Glue them inside the holes of the disc and of the horizon, to stand as pillars. While the glue is drying, check the distance between the horizon and the disc.

Cut the skewer 21.2cm long, pass it through the sphere, add the 2 hour wheels ( wheel 'N' at the north pole). add small nuts so the distance between the surface of the sphere and the meridian is kept at 1cm.

Insert the ends of the skewer on the notches of the meridian (There has to be some friction here, so the meridian holds the axis firmly). Check the sphere can spin freely.

Set the sphere on the stand, from above, so that the meridian fits inside the concave cradle on the stand.

Check that the sphere can still spin freely, and that you can change the axis's tilt by sliding the meridian on its cradle.

If you can't use a laser-cutting machine, consider building a stand from 3mm thick cardboard. It's strong enough to support the very light sphere.

First draw the pieces on the cardboard (use the dimensions from the first pdf here).

Then carve the pieces with a cutter.

Some pieces need graduations. Print the 2 other pdf documents, cut and glue the graduations on the corresponding pieces.

Glue the stand as in the picture provided.

Glue the sphere's axis on the meridian (2dn photo).

Glue the 8 wooden rods on the disc, so the horizon stands 13cm above the disc.

Alternatively, the stand can be 3D printed. Estimated printing times for these 3 STL files are: 2.5h, 1.15h and 1h40.

You'll still need wooden rods to make 8 13.3cm pillars for the horizon, as described previously.

Glue the pillars to the base and the horizon so the horizon is 13cm above the base.

Set the celestial sphere to the meridian and set the meridian on the stand as previously described for the wooden stand.

Though I can't write a complete user guide to this celestial globe in English, here are some basics to help you explore this extraordinary instrument:

1. any star below the horizon is... well below the horizon, hence invisible to the observer. When a star is just at the eastern horizon, it's just rising (beginning of the day, if this star is the Sun).
2. to set the globe to a given latitude on earth, slide the meridian on its cradle so the corresponding graduation is just level with the horizon. For a place on the northern hemisphere, the north pole must be above the horizon.
3. on the horizon the letter 'E' indicates true east, the letter 'O' is for true west.
4. the red line going all around the sky map is the ecliptic: the Sun's path across the year. It's labeled with dates ('1.3' is March 1st, etc.). Small dots for the 5th, 10th, 15th, 20th, 25th, and 30th days of the month. To set a date, dig a pin on the corresponding date on the ecliptic. Make sure the pin doesn't hit the horizon when spinning the sphere.
5. to reproduce the daily motion of stars, turn the sphere so stars rise near the east. Clockwise, as seen from the north pole, anticlockwise from the south pole.
6. to read solar time : after placing a pin for the Sun, turn the hour wheel so that the '12' is towards the pin. Then read solar time on the upper part of the hour wheel, aligned with the meridian.
7. Suggestions:
8. see how sunrise/sunset times change along the year.
9. see how sunrise/sunset times change as your latitude is closer to the Equator or to the poles.
10. see why some stars will be visible only at some time of the year, others always visible, others never.

I you can read french, a more complete user guide is available for download on this page: https://www.astrolabe-science.fr/maquette-globe-celeste/