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About the Regular Stargazing Parties

What are the Regular Stargazing Parties?


Regular Stargazing Parties are held twice per month at NAOJ Mitaka Campus (limited capacity, reservations required). In cities, street lamps conceal the dark night sky. But that doesn’t change the fact that even now the Universe stretches out over our heads. We want many people to experience the splendor and wonder of the Universe and embrace an interest in astronomy at these Regular Stargazing Parties.

Objects Observed

月 Moon
火星 Mars
土星 Saturn

The chosen observation targets are concentrated around the Moon, planets, and double stars which are easy to observe in Tokyo’s bright night sky. With the 50-cm Telescope for Public Outreach, the impressive craters on the Moon, Jupiter’s striped pattern and the Galilean Satellites, Saturn’s Ring, etc. can be seen clearly. The colors of bright stars can also be easily discerned; second magnitude stars appear very beautiful.
Sometimes the observation targets also include faint objects like nebulae and star clusters. We choose relatively easy to observe celestial objects, but in truth they look paler than what is seen in photos.

Calendar & Registration

Order of Events at the Regular Star Parties

Some of the event staff can speak English, but the Regular Stargazing Parties are conducted primarily in Japanese. We appreciate your understanding and cooperation.

1. Orientation


First, in a lecture room there is a simple explanation in Japanese about that night’s observational targets. The explanation is given by undergraduate or graduate students conducting research in astronomy. They work hard to come up with new material for each time. Please enjoy.

2. The 50-cm Telescope for Public Outreach

The 50-cm Telescope for Public Outreach

Next, everyone relocates to the 50-cm Telescope for Public Outreach and observes that night’s target objects. We use the waiting time to explain the constellations and planets visible that night (minimal English).

3. Astronomical Observations with Small Telescopes

Astronomical Observations with Small Telescopes

After observations with the 50-cm Telescope for Public Outreach are finished, please enjoy observations with the small telescopes prepared near the dome (minimal English). The observational targets of the small telescopes are not predetermined; they are chosen flexibly, based on the state of the clouds that evening. After observations are finished, you are free to leave at your own leisure. Please take care as you return home.

In the case of rain or bad weather, astronomical observations can’t be conducted.
The explanation will be extended by about 15-20 minutes.
Instead of astronomical observations, commentary using the Four Dimensional Digital Universe visualization software Mitaka or a tour of the 50-cm Telescope for Public Outreach will be offered (both minimal English). (Telescope tours aren’t possible when it is raining.) Whether astronomical observations will be conducted or canceled will be announced that day via Twitter (Japanese language only.) Please check this on the day of the Regular Stargazing Party.

About the 50-cm Telescope for Public Outreach


The 50-cm Telescope for Public Outreach was established in 1994, with public access as one of the primary motivations. Regular Stargazing Parties with this telescope started in 1996. Since then, many people have experienced the wonder of astronomical observations. In addition to Regular Stargazing Parties, the telescope is used for activities like comet research observations, capturing images for public outreach, and student practice observations.

Basic Capabilities of the 50-cm Telescope for Public Outreach
Configuration Cassegrain Reflecting Telescope
Mount Equatorial Fork
Aperture (Primary Mirror Diameter) 50 centimeters
Focal Length 6030 millimeters
Resolving power 0.3 arcseconds (theoretical limit)
Light Gathering Power About 5000 times that of the naked eye
Limiting Magnitude for Observing by Eye 16th Magnitude (ideal sky conditions)
Limiting Magnitude with the Cooled CCD 21st Magnitude (in Mitaka with ideal sky conditions)