The Eastern Anatolia Observatory and the 4-Metre DAG400 Telescope
Ramazan Şahin, PhD · · 4 min read · Updated
Site, sky quality and the key specifications of the 4-metre DAG400 telescope at the Eastern Anatolia Observatory, 3,170 metres up on Mount Palandöken.
The Eastern Anatolia Observatory (DAG) is one of the two large observing facilities run by the Türkiye National Observatories. Built on the Karakaya Hills of Mount Palandöken near Erzurum, it houses a telescope with a 4-metre primary mirror. The institution describes DAG as the largest observatory in Türkiye and the first in the country designed to observe in the infrared. This article summarises its institutional setting, site, sky conditions and the main technical features of the DAG400 telescope, based on figures published by the institution.
Institutional setting
The Türkiye National Observatories were created as a joint undertaking of Atatürk University and TÜBİTAK under Law No. 6550 on the support of research infrastructures. The organisation was accredited on 25 April 2023, received the status of an advanced research infrastructure and became the first joint research infrastructure under that law. Its headquarters are in Erzurum and its support office is in Antalya. The two core facilities are DAG, established within Atatürk University's Astrophysics Research and Application Centre (ATASAM), and the TÜBİTAK National Observatory (TUG), in service since 1997.
Site and access
The observatory stands at 3,170 metres on the summit of the Karakaya Hills, south-west of Erzurum city centre and next to the Konaklı ski resort. The institution gives its coordinates as roughly 39° 46′ N and 41° 13′ E. About 27 km of road lead from the city to the ski resort, followed by some 8 km of mountain road; the institution puts the journey at a little over half an hour.
The altitude is a deliberate choice. Part of the near-infrared light is absorbed by water vapour in the atmosphere, and the higher an observatory stands, the less air and water vapour remain above it. A high summit also means a thinner layer of turbulent air along the path of starlight.
Climate and sky quality
The published weather summary is based on readings from an on-site Vaisala sensor between 2022 and June 2025. Over that period the mean temperature was 3 °C, with a low of −26 °C and a high of 25 °C. Air pressure averages about 521 hPa, roughly half the sea-level value. Winds come mostly from the south-south-west at an average of 6 metres per second. Snow stays on the ground for about seven months a year, with an average depth of 3.5 metres and a maximum of 7 metres. Weather stations in the telescope buildings track conditions, and an all-sky camera shows the cloud cover in real time.
Three figures sum up the observing quality. The sky background brightness is 21.4–21.8 mag/arcsec²; a larger number means a darker sky. Astronomical seeing, which describes how much the atmosphere spreads out a star image, is given as 0.93 arcseconds. Around 240 clear nights are expected each year. The institution sets these against general observatory averages of 0.6–1.0 arcseconds of seeing and 200–300 clear nights a year.
The DAG400 telescope
DAG400 is a Ritchey–Chrétien telescope with a 4.0-metre primary mirror. In this design both the primary and the secondary mirror are hyperbolic, which removes the coma that otherwise limits wide-field imaging. The focal ratio is f/14.2 and the effective focal length is 56 metres. The telescope is designed for visible (VIS) and near-infrared (NIR) observations.
DAG400 sits on an altitude-azimuth mount. This keeps a large, heavy telescope compact and well balanced, but the field of view slowly rotates while a target is being tracked. The telescope therefore uses a K-mirror field derotator called KORAY. The field of view quoted by the institution is 24′ × 24′ in seeing-limited mode and 7′ × 7′ in diffraction-limited mode.
What sets the telescope apart is not only its mirror size but also its optical technology. Active optics typically reshapes the primary mirror through actuators behind it, correcting slow deformations caused by gravity and temperature changes. Adaptive optics offsets the effect of atmospheric turbulence, which changes within fractions of a second. According to the institution, the two technologies make the telescope suitable for science at an international level.
Other telescopes and infrastructure on site
Two more observing systems share the site. ATA050, operated in partnership with Atatürk University, is a 0.5-metre telescope fitted with cameras and spectrographs for visible-light imaging and spectroscopy. DAGTPS is an atmospheric turbulence profiling system made of two 30-centimetre telescopes that continuously measures the conditions above the observatory.
Around the telescope building stand a service building with the control room and a mirror-coating unit, a separate HVAC building, an energy building whose transformers and generators are monitored through a SCADA system, and a security building. According to the institution's infrastructure table, the site has a contracted electrical capacity of 1,200 kVA and a 1 Gbit/s fibre internet connection.
Current status
According to the institution's history page, installation of DAG was completed in 2024. The same page states that the observatory will first offer photometric and coronagraphic observations in the visible and the infrared, followed by spectroscopic observations. Current news is published on the institution's website.
References
- Erzurum DAG Campus · Türkiye National Observatories (trgozlemevleri.gov.tr)
- DAG400 Telescope · Türkiye National Observatories (trgozlemevleri.gov.tr)
- History · Türkiye National Observatories (trgozlemevleri.gov.tr)
- About · Türkiye National Observatories (trgozlemevleri.gov.tr)
Last accessed: 24 September 2026.