University Lowbrow Astronomers

Homestar, A Compact Home Planetarium.

by Yasuharu Inugi
Printed in Reflections: August, 2006.

The Universe for less than 3 cents per star! Yasuharu Inugi reviews the “Sega” planetarium “HOMESTAR.”


A compact, home use planetarium named “Homestar” was released last year by Sega Toys in Japan. The product was co-designed with Takayuki Ohira, a Japanese Planetarium designer. Ohira is well known in Japan for his “Mega Star” planetariums that can project more than a million stars. Some people who go to his planetariums take binoculars with them.

“Homestar” does not project a million stars, but rather, it projects about 10,000 stars. I bought one last December and showed it to the Lowbrows, first at John Causland’s house at the January ACNO gathering, and then at a meeting later. Since then, it has been a good toy for me and I have been using it frequently.

How it works

Homestar is powered by 5~6VDC, which can be supplied either by an AC/DC adaptor which comes with the unit, or four size C batteries. It comes with two star image discs, with or without constellation lines. This planetarium uses a lens system. Star images are photo-printed in a tiny data disc, which is set horizontally into the unit. There is an LED bulb below the disc, and star images go upward, go through four element lens to be sharpened, then projected upward, to the ceiling or a dome.

Focus adjustment is done by turning the dial at the top. The rotation function makes the star images to go around Polaris, CW or CCW, and complete a round in about 12 minutes. It also has automatic turn-off timer with 15, 30, or 60 min setting. There is also a shooting star function which shows imitated meteor image with random timing. There is no function to project planets. Optional southern hemisphere sky data discs are available.

Personal opinion about the unit

The unit is surprisingly light and small. The first impression I had from the size was it just looked like a cheap toy. But the projected images were much more than I first guessed from the appearance of the unit. It is quite nice to be able to see some 10000 stars on my ceiling, which is more than you can see with your naked eye at either Peach Mountain or Lake Hudson. Unlike the conventional planetarium, the light ray from the projector is not a half sphere but rather shaped like a cone. This I believe is because Homestar is primarily designed to be projected onto a flat surface, like a ceiling at home. The light ray angle from north horizon to south horizon is probably about 90 degrees (I don’t have the exact number). Thus, the entire sky above horizon is projected in a disc. Constellations inevitably appear a little smaller than what you see under the real night sky. The lower the ceiling, the smaller the images seem to appear. Also, images get fuzzy and a little distorted near the horizon. The Milky Way is clearly seen, both in summer and winter sky. Images of stars for most constellations, especially near Zenith, are very clear. Stars appear brighter than actual ones. Especially, I feel that the faint stars are a little too bright. But maybe this is inherent in design. There is no color in the stars. They are all white.

Some large open clusters (M44, M45, Hyades, Coma Cluster, etc.) are visible. I have noticed some major non-stellar fuzzy objects like M8, M13, etc., are missing. I believe this is because the disc data is made by stellar data and do not have non-stellar objects.

The images get much nicer when a dome is used. At the July meeting, Norb Vance showed us his Homestar unit and projected images on a half sphere dome at the EMU astronomy department. Wow, it was so much nicer. I am quite impressed, and now planning on making a hemisphere dome for mine. The recommended projection distance, according to the manual, is 2.0~2.3 m (6.6~7.5 ft), but I found a much larger distance, like a 10~12 ft range, will still produce fairly descent image. The rotation function is nice, but I sometimes feel that it is too fast when you are observing, and it is too slow when you want to go from winter sky to summer sky. The auto-off timer comes handy, since I often use it when going to bed. The shooting star function at first appeared nice, but after a while I am not too crazy about it, because the pattern is always the same, just timing is different.

Overall, I like the unit very much. I think it is well worth the money I spent. It has been a good tool to learn constellations and enjoy star gazing especially on cloudy Michigan nights.


Dimensions: 167 x 159 x 151 (mm)

Weight: Approx. 1 kg

Power consumption: Approx. 3W

Recommended projection distance: 2.0~2.3 m (6.6~7.5 ft)

The product comes with:

The AC/DC converter is rated for Japanese 100VAC input, but I have been using it for our US 115VAC input and have not encountered any problem.


The suggested retail price in Japan from the manufacturer is 20,790 yen. It is available from some importers in US for about $250 or so.


Home, School, etc. It would be great for a small classroom.

Improvements I want

I have some suggestions for improvement for Sega Toys, maybe for the next version of Homestar.

New! About “Homestar Pro” coming end of 2006

I just learned that the improved version “Homestar Pro” will be available by the end of this year, for about $300. It will have improved images around the edge and bright stars (mag 4 and above) will have colors.

Photo Credits

The image of Yasu was taken by Dave Snyder; the other images were all taken by Yasuharu Inugi.


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