In astronomy, there are three types of dawn. They are astronomical, nautical, and civil dawn. The sunlight is starting to appear on the east horizon when the Sun altitude is 18 o below the horizon. Hence, there is a change on the sky brightness. The sky brightness can be affected by the moon phases. The sky brightness level is monitored by Sky Quality Meter (SQM). The SQM was installed upward to the zenith. There are 4 locations of measurement in Yogyakarta. The data has been collected for nine months to obtain the complete moon phases. The beginning of astronomical dawn is time when the sky brightness level is starting to decrease. The moving average algorithm was employed to determine the beginning of astronomical dawn. The time when the astronomical dawn begins is compared with the sun altitude calculation. The sun altitude calculation has been done using accurate times software. The difference of the beginning of astronomical dawn by measurement and calculation are 18.61±6.81 minutes, 19.12±3.28 minutes, 31.12±7.76 minutes, and 27.24±8.04 minutes, on the new moon (0), on the first quarter (0.25), on the full moon (0.5) and on the last quarter (0.75), respectively. The weather condition is also contributing to the results.

<p class="AbstractEnglish"><strong>Abstract:</strong> Determination of the beginning of the prayer time is very important for Muslims because it is one of the prayer pillars. However, the determination of beginning morning prayer is still difficult, because the sun is below the horizon. The determination of the beginning of dzuhur, ashr, and maghrib times are easier since the sun's shadow is still clearly visible. The sun position is determined by sun declination. The sun declination value is given a positive sign (+) when it is north of the sky equator and negative sign (-) when it is to the south of the celestial equator. This research method uses the experimental method. The determination of the subuh time has been done by measuring sky brightness level that was measured by SQM. There is a difference between the beginning of morning prayer time between the Accurate Times software calculation and the measurement. In the sun declination variation, difference data ranged from 21 - 36 minutes. From this study, it was concluded that the value of sun declination affected the beginning of dawn time.</p><p class="KeywordsEngish"><strong>Abstrak:</strong> Penentuan awal waktu salat yang tepat penting bagi umat muslim, karena merupakan salah satu rukun salat. Namun, penentuan awal waktu salat subuh masih sulit, karena matahari berada di bawah horizon. Penentuan awal waktu zuhur, asar, dan magrib lebih mudah karena bayangan matahari masih terlihat jelas. Posisi matahari ditentukan oleh deklinasi matahari, nilai deklinasi matahari diberi tanda positif (+) ketika berada di sebelah utara ekuator langit dan negatif (-) ketika berada di sebelah selatan ekuator langit. Metode penelitian ini menggunakan metode eksperimen. Penentuan awal waktu subuh dengan menggunakan pengukuran Tingkat Kecerahan Langit (TKL) ini diukur dengan <em>Sky Quality Meter (SQM)</em>. Terdapat selisih awal waktu salat subuh antara perhitungan <em>Software Accurate Times</em> dan pengukuran. Pada variasi deklinasi matahari diperoleh data selisih berkisar antara 21-36 menit. Dari penelitian ini disimpulkan bahwa nilai deklinasi matahari berpengaruh terhadap awal waktu subuh.</p>

Polusi cahaya sangat berpengaruh terhadap kecerahan langit. Tingkat kecerahan langit dapat diukur dengan Sky Quality Meter (SQM). Hasil data SQM sangat banyak, perlu aplikasi untuk mempermudah pengolahan datanya. Fitur Visual Basic Microsoft Excel dapat membantu pengolahan data SQM. Penelitian menggunakan metode observasi tingkat kecerahan langit dengan SQM. Analisis data menggunakan metode moving average. Pengembangan perangkat lunak menggunakan model waterfall dengan lima tahapan permodelan, yaitu: analisis, desain, implementasi, pengujian, dan perawatan. Model pengembangan waterfall mampu untuk membuat sistem pengolahan data SQM, data dengan berbagai kolom dapat dipilih secara otomatis dan cepat sehingga dapat dibuat grafik tingkat kecerahan langit terhadap waktu.Light pollution dramatically affects the brightness of the sky. Sky brightness level can be measured using Sky Quality Meter (SQM). SQM data results are huge data. It needs an application to facilitate data processing. Microsoft Excel Visual Basic features can assist the SQM data processing. The study used observational methods of sky brightness with SQM. Data analysis using the moving average method. Software development used the waterfall model with five stages of modeling, namely: analysis, design, implementation, testing, and maintenance. The waterfall development model was able to create an SQM data processing system. The data with various columns can be selected automatically and quickly. Hence, it is able to graph the level of sky brightness versus time.

Penelitian ini bertujuan untuk menemukan nilai frekuensi akustik dari botol. Resonansi Helmholtz yang digunakan dalam penelitian ini adalah frekuensi Helmholtz pada botol kaca bekas sirup. Penelitian ini dilakukan dengan memanfaatkan sebuah botol yang memiliki leher untuk mengetahui nilai resonansi Helmholtz. Pengukuran resonansi Helmholtz menggunakan aplikasi dari android yaitu spectroid karena dapat mengukur besar frekuensi dan dB. Hasil yang diperoleh yaitu terjadi penurunan frekuensi pada variasi volume ke 2.1224955 m 3 . Berdasarkan data yang diperoleh sesuai dengan prinsip Helmholtz. Semakin besar volume udara maka akan semakin kecil frekuensinya. Sedangkan nilai dB akan kecil jika volume makin kecil.This is an open access article under the CC-BY-SA license

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