# A Survey of Big Data Archives in Time-Domain Astronomy
## 3 Time-Domain Astronomy
#### Science Project and Virtual Observatory in the Era of Big Data in Astronomy  
Many scientific operations, including astronomy, have become data-intensive in the age of big data and archives. The rapid advancement of technology, particularly in computer hardware (with low-cost, high-capacity storage, and processing) and microelectronic (such as: charge-coupled devices (CCD)) devices [27], has revolutionized the majority of natural science through an explosion in the number of measurements and simulation data [28]. Astronomers use a blink comparator to compare two-night sky images and identify differences. It was possible to \"blink\" back and forth between two images of the same part of the sky obtained at various points in time using this technique. Asteroids and comets could be differentiated into images taken a few day apart since they would appear to oscillate between two positions. On the contrary, all the other stars stood still. Photographs separated by a longer period of time can be used to discover stars with large proper motion and distinguish binary stars from optical doubles, and variable stars [29]. [PERSON] used the blink comparator to discover Pluto. On loan from the Lowell Observatory and on display in the Museum of Washington is DC's Exploring the Planets Gallery [30]. Modern astronomy has come a long way since [PERSON] made his initial views of stars in 1609 with his refracting telescope [31]. Astronomy advanced significantly in the first decade of the 1600s with the discovery of an optical telescope and its use to study the night sky. Global astronomical research projects aim to meet the data volume and computational challenges associated with tackling the main research problems. The virtual observatory has been proposed as the response of the astronomical community to the challenges passed by the new massive and complex data sets [32]. The following examples of astronomical projects are data-intensive, and require a virtual observatory for worldwide scientific collaboration. Using a 7.2 square degree camera mounted on the [PERSON] 48-inch (1.2 m) [PERSON] telescope, Palomar Transient Factory (PTF) has been in service since 2009 [33; 34]. These telescopes observe the night sky in the visible and infrared spectra. It is a fully automated, wide-field survey aimed at the systematic exploration of the optical transient sky [35]. Two automatic reduction pipelines received data from the camera. Lawrence Berkeley National Laboratory (LBNL) [36] runs a near-real-time image subtraction pipeline to recognize optical transients minutes after the images are recorded. To arrive at a collection of probabilistic claims concerning the scientific classification of the transients, the output of this pipeline is submitted to UC Berkeley, where a source classifier analyzes it [33]. The images were also entered into a database at the Infrared Processing and Analysis Center (IPAC) within a few days of capture. Calibration and object detection are performed on each incoming frame before they are combined into a database. Using the P48 photometric follow-up telescope, the P60 automatically generates colors and light curves for intriguing transients [37]. Fifteen more telescopes were used for photometric and spectroscopic follow-ups as part of the PTF cooperation. The coordination of observations and reporting is handled by an automated system that collects data from the Berkeley classification engine and distribute it to various follow-up facilities [33]. The intermediate Palomar Transient Factory (iPTF) [38], which began operation in 2012, is the successor of the PTF. The image processing and differencing pipeline innovations have made it possible to receive transient candidates significantly faster (from 30-60 min to 10 min in iPTF) than before [38,39]. The PTF/iPTF generated 1 gigabyte data per 90 s, and which was approximately 0.05 petabytes per year. The iPTF has conducted a series of fast-cadence studies to identify and characterize young supernovae and rapidly changing transients.