The Sun-Earth Lagrange point L4, which is called a parking space of space, is considered one of the unique places where solar activity and the heliospheric environment can be observed continuously and comprehensively. The L4 mission affords a clear and wide-angle view of the Sun-Earth line for the study of Sun-Earth connections from remote-sensing observations. The L4 mission will significantly contribute to advancing heliophysics science, improving space weather forecasting capability, extending space weather studies far beyond near-Earth space, and reducing risk from solar radiation hazards on human missions to the Moon and Mars. Our paper outlines the importance of L4 observations by using remote-sensing instruments and advocates comprehensive and coordinated observations of the heliosphere at multi-points including other planned L1 and L5 missions. We mainly discuss scientific perspectives on three topics in view of remote sensing observations: (1) solar magnetic field structure and evolution, (2) source regions of geoeffective solar energetic particles (SEPs), and (3) stereoscopic views of solar corona and coronal mass ejections (CMEs).

Introduction
Solar Magnetic Field Structure and Evolution
    Investigation of Global Solar Photospheric Fields
    Disambiguation of Solar Vector Magnetograms
    Observations of the Sun's Polar Magnetic Fields
Source Regions of Geoeffective SEPs
    Face-on Observations of Geoeffective SEP Source Regions
    SEP Study Based on EUV Wave Parameters
    SEP Study Based on CME Parameters
Stereoscopic Views of the Solar Corona and CMEs
    Coronal Structures and Solar Wind Origin
    CME 3D Properties and Propagation
Summary
Acknowledgments
References

• Yong-Jae Moon(School of Space Research, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea, Department of Astronomy and Space Science, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea) Corresponding author
• Kyung-Suk Cho(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, Department of Astronomy and Space Science, University of Science and Technology, Daejeon 34113, Republic of Korea)
• Sung-Hong Park(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, Department of Astronomy and Space Science, University of Science and Technology, Daejeon 34113, Republic of Korea)
• Eun-Kyung Lim(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Roksoon Kim(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Donguk Song(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan)
• Jongyeob Park(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Eunsu Park(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Harim Lee(Department of Astronomy and Space Science, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea)
• Hyun-Jin Jeong(Department of Astronomy and Space Science, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea)
• Jihye Kang(Department of Astronomy and Space Science, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea)
• Jinhye Park(Department of Astronomy and Space Science, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea)
• Kangwoo Yi(Department of Astronomy and Space Science, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea)
• Il-Hyun Cho(Department of Astronomy and Space Science, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea)
• Hyeonock Na(Department of Astronomy and Space Science, Kyung Hee University, Yongin, Gyeonggi 17104, Republic of Korea)