Sains Malaysiana 49(2)(2020): 439-445

http://dx.doi.org/10.17576/jsm-2020-4902-23

Identifying Light Pollution Sources at Two Major Observatories in Malaysia

(Pengenalpastian Sumber Pencemaran Cahaya di Balai Cerap Utama di Malaysia)

MOHAMMAD R. TAHAR^1,2, NAZHATULSHIMA AHMAD¹ & NUR H. ISMAIL¹

¹Department of Physics, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Federal Territory, Malaysia

²National Space Agency, Pusat Angkasa Negara, 42700 Banting, Selangor Darul Ehsan, Malaysia

Received: 19 August 2019/Accepted: 1 November 2019

ABSTRACT

A spectral observation and analysis were conducted in order to identify the main contributor of sky brightness at two of Malaysia's most active observatories. The light pollution observations were carried out under moonless clear night sky with a 90 mm refractor telescope and SBIG's Self Guiding Spectrograph. We found that the main contributor to Balai Cerap Teluk Kemang (BCTK) sky brightness is High Pressure Sodium (HPS) street lighting due to its number and density used within 5 km radius of the observatory. HPS spectral lines dominate the spectrum between 556 - 640 nm, agrees with the orange hue visible to the naked eye. The intensity due to HPS lighting is so high that there was no trace of the concerned white LED spotlight less than 1 km away. However, some traces of elements from Mercury Vapor (MV) lamps at 3.6 km distance managed to reach the observatory in the green spectrum. The finding concludes that the nearby LED spotlight does not affect the night sky brightness over BCTK. Meanwhile, Langkawi National Observatory (LNO) sky profile was also observed during heavy fishing season as comparison. The sky spectra for LNO was similar to BCTK in the reds except for a very distinct peak in green region corresponding highly with green MV (532 - 547 nm) with peaks at 536 nm and 546 nm, matches the lamps used for squid fishing around the island. The intensity of the green MV light matches the intensity of HPS light sources, during the observation period of peak squid season in January. This made LNO a far less favorable condition for astronomical observing site compared to BCTK. We also found that LNO sky has brightened 3.767 times compared to finding of 2013.

Keywords: Light pollution; observatory; sky brightness; sky glow

ABSTRAK

Cerapan dan analisis spektrum telah dijalankan bagi mengenal pasti penyumbang utama kepada pencemaran cahaya di dua balai cerap paling aktif di Malaysia. Hasil kajian mendapati punca utama pencemaran langit di BCTK adalah daripada lampu jalan HPS (High Pressure Sodium). Ia berpunca daripada jumlah penggunaan terbanyak dan kepadatan yang tinggi dalam lingkungan jarak 5 km. Garisan pancaran HPS mendominasi spektrum langit BCTK pada 556 - 640 nm, selaras dengan warna jingga langit yang dilihat dengan mata kasar. Pancaran HPS amat kuat sehingga tiada langsung kesan spektrum daripada lampu sorot LED kurang dari 1 km dari BCTK. Walau bagaimanapun, garisan pancaran lampu wap raksa lebih kurang 3.6 km daripada BCTK dapat dilihat pada panjang gelombang 535.7 nm. Kajian mendapati lampu LED di kawasan bersebelahan tidak memberi sebarang kesan kepada pencemaran langit BCTK. Sebagai perbandingan, spektrum langit Observatori Negara Langkawi (ONL) pada musim mencandat sotong juga digunakan dalam kajian ini. Spektrum cahaya langit ONL hampir menyerupai BCTK dalam cahaya merah, tetapi dengan tambahan garisan pancaran hijau yang amat jelas pada 536 nm dan 546 nm, iaitu sepadan dengan lampu merkuri hijau yang digunakan oleh bot mencandat sotong sekitar Langkawi. Keamatan cahaya daripada lampu merkuri hijau menandingi keamatan lampu HPS pada waktu cerapan dibuat pada bulan Januari. Ini menunjukkan pada waktu tertentu, langit ONL adalah lebih tercemar berbanding langit di BCTK untuk pencerapan astronomi. Kajian ini juga mendapati peningkatan tahap kecerahan langit LNO yang meningkat 3.767 kali ganda berbanding cerapan yang dibuat pada tahun 2013.

Kata kunci: Balai cerap; kecerahan langit; pencemaran cahaya; spectrum

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*Corresponding author; email: n_ahmad@um.edu.my