National Astronomical Observatory of Japan Mitaka Campus

What the Mitaka Campus is

The National Astronomical Observatory of Japan Mitaka Campus, in Osawa, Mitaka City, Tokyo, is the headquarters of the country's astronomical research, and ten of its structures, built between 1921 and 1930, were entered in the national register of tangible cultural properties between 1998 and 2014. They stand across a wooded site that still keeps patches of the old Musashino coppice: domes for telescopes, small windowless boxes built to protect instruments, a gate and a gatekeeper's lodge.

Every one of these buildings was shaped by a measurement problem. Positional astronomy needs a telescope that does not feel the floor shake, a roof that opens along the line of sight, and a structure set true to the north-south meridian. The observing floor of the Great Equatorial Telescope Dome rose and fell like a lift so that the astronomer could stay at the eyepiece; the two meridian mark rooms sit exactly 100 metres north and south of the Gautier Meridian Circle Building because that is where the reference marks had to be.

The ten registrations came in three waves. The Solar Spectrograph Building was listed in 1998, the First and Great Equatorial Telescope Domes in 2002, and the remaining seven in 2014, each as a Registered Tangible Cultural Property.

From Azabu to Mitaka

The observatory began in 1888, when the astronomical observatory of the University of Tokyo, the naval observatory and the geographical bureau of the Home Ministry were merged into the Tokyo Astronomical Observatory at Azabu Iikura, in central Tokyo. The city grew, the night sky brightened, and the site was cramped. Land was secured in the village of Mitaka in 1909, and the move began around 1914.

What finished the job was a disaster. The Great Kanto Earthquake of 1 September 1923 wrecked the Azabu premises. Instruments already crated for the move survived, and the relocation accelerated sharply. That is why nine of the ten registered structures at the National Astronomical Observatory of Japan Mitaka Campus date from the tight span between 1921 and 1926.

The site is owned today by the Inter-University Research Institute Corporation National Institutes of Natural Sciences. Front-line observation has long since moved elsewhere, and the older buildings now serve as preserved monuments and small museums.

Walking the grounds

The main gate opens on the east side of the site and is still the entrance in daily use. Just inside it, on the north, stands the wooden gatekeeper's lodge that serves as the visitor reception, and this is where every visit starts.

A straight road runs west from there. The First Equatorial Telescope Dome and the Great Equatorial Telescope Dome face each other across it, the first under a dome less than six metres across, the second under one that brings the building to 19.5 metres. Further west the Solar Spectrograph Building rises as a tower, and the northwestern corner holds the Old Library and Storehouse, the Repsold Transit Instrument Building and the Gautier Meridian Circle Building.

The First and Second Meridian Mark Rooms lie about 100 metres south and north of the Gautier Meridian Circle Building. Neither is on the list of buildings open to visitors, and both fall outside the marked route. Visitors to the National Astronomical Observatory of Japan Mitaka Campus are asked not to step off the route or into the undergrowth, so these two are seen from a distance if at all.

Visiting

The grounds are open daily from 10:00 a.m. to 5:00 p.m., with last admission at 4:30 p.m., and close only for the New Year period from 28 December to 4 January. Admission is free, and individuals or small groups need no reservation.

Reception is at the guard house immediately inside the main gate: scan the posted QR code and fill in the form, or write your details on the paper visitor slip. You will be handed a visitor sticker for each person, to be worn somewhere visible. Facility inspections, construction work and severe-weather warnings can close the campus at short notice, so it is worth checking the day's notice before travelling out.

Photography along the route is allowed for private use. If images are posted publicly, other visitors should not be identifiable. Eating and drinking are confined to the rest room and the outdoor benches.

On clear days the First Equatorial Telescope Dome runs a solar viewing session, with staff operating the 20-centimetre refractor so that visitors can look at sunspots. It is free and needs no booking, but it pauses from June to September because of the heat.

Drivers use the paid visitor car park, entered from the rear gate on the north side; the main gate does not connect to it. Parking costs 500 yen for the first three hours and 200 yen for each hour after that, is available from 8:30 a.m. to 5:30 p.m., and holds 54 cars. Bicycles and motorcycles use the free racks beside the main gate.

Getting there

Every route ends at the Tenmondai-mae bus stop. From the south exit of Musashi-Sakai Station on the JR Chuo Line, stand 3, the Odakyu Bus route 境91 takes about 15 minutes and costs 250 yen. From Mitaka Station south exit, stand 5, route 鷹51 takes about 20 minutes for 250 yen. From Chofu Station north exit, stand 14, routes 境91 and 鷹51 take about 15 minutes for 250 yen, while the Keio Bus route 武91 from stand 13 at the same exit costs 230 yen. From Musashi-Koganei Station south exit, stand 6, routes 武91 and 武93 take about 20 minutes for 300 yen.

The address is 2-21-1 Osawa, Mitaka City, Tokyo, and the telephone number is 0422-34-3600. The bus stop is a short walk from the main gate, and everything beyond it is on foot.

The ten registered structures

These are the ten entries at the National Astronomical Observatory of Japan Mitaka Campus, with the year of construction and the year of registration.

• Main Gate (1925, registered 2014)
• Guard House (1924, registered 2014)
• First Equatorial Telescope Dome (1921, registered 2002)
• Great Equatorial Telescope Dome (1926, registered 2002)
• Solar Spectrograph Building (1930, registered 1998)
• Old Library and Storehouse (1930, registered 2014)
• Repsold Transit Instrument Building (1925, registered 2014)
• Gautier Meridian Circle Building (1924, registered 2014)
• First Meridian Mark Room (1925, registered 2014)
• Second Meridian Mark Room (1925, registered 2014)