International Space Agencies – Missions and Discoveries

Solar and Heliospheric Observatory (SOHO) discovers 5000th Comet


From UPSC perspective, the following things are important :

Prelims level: Solar and Heliospheric Observatory (SOHO)

Mains level: NA

Why in the news?

A Czech citizen has spotted a comet in an image from the Solar and Heliospheric Observatory (SOHO) spacecraft, which has now been confirmed to be the 5,000th comet discovered using SOHO data.

Solar and Heliospheric Observatory (SOHO)

  • The SOHO is a spacecraft jointly operated by the European Space Agency (ESA) and NASA.
  • Launched in December 1995, its primary mission is to study the Sun, particularly its outer atmosphere, known as the corona, and the solar wind.
  • SOHO observes the Sun in various wavelengths of light, enabling scientists to study phenomena such as sunspots, solar flares, and coronal mass ejections.
  • SOHO orbits the Sun at Lagrange Point L1, about 1.5 million kilometers (nearly 1 million miles) from Earth, providing an uninterrupted view of the Sun.
  • Its observations have led to discoveries such as-
  1. Identifying the source regions of solar wind,
  2. Tracking solar eruptions, and
  3. Monitoring changes in the Sun’s activity over its 11-year solar cycle.


What are Lagrange Points?

  • Lagrange Points are named after the French mathematician Joseph-Louis Lagrange who discovered them in 1772.
  • They are specific points in space where the gravitational forces of two large bodies, such as the Earth and the Sun, or the Earth and the Moon, balance the centrifugal force felt by a smaller body.
  • These points are stable locations where objects can maintain their relative positions concerning the larger bodies, without drifting away or falling towards them.

There are five Lagrange Points, denoted as L1, L2, L3, L4, and L5:

  1. L1: Located on the line connecting the two large bodies and closer to the smaller body, L1 is particularly useful for space observatories like the Solar and Heliospheric Observatory (SOHO) because it provides an unobstructed view of the Sun from Earth’s perspective.
  2. L2: Situated on the opposite side of the smaller body from the larger one, L2 is an excellent location for deep space observatories such as the James Webb Space Telescope (JWST) because it remains relatively shielded from solar interference.
  3. L3: Located on the line connecting the two large bodies but on the opposite side of the larger body from the smaller one, L3 is less stable and less frequently used than the other Lagrange Points.
  4. L4 and L5: These points form equilateral triangles with the two large bodies, with the smaller body at the third vertex. L4 precedes the smaller body in its orbit, while L5 follows it. These points are stable and have been found to accumulate natural objects, such as asteroids, known as Trojan asteroids.



2013: Consider the following phenomena:

1. Size of the sun at dusk

2. Colure of the sun at dawn

3. Moon being visible at dawn

4. Twinkle of stars in the sky

5. Polestar being visible in the sky

Which of the above are optical illusions?

a)    1, 2 and 3

b)    3, 4 and 5

c)    1, 2 and 4

d)    2, 3 and 5


Practice MCQ:

Regarding the Solar and Heliospheric Observatory (SOHO), consider the following statement:

1.    SOHO spacecraft was launched in December 1995.

2.    It is jointly operated by the European Space Agency (ESA) and NASA.

3.    It orbits the Earth in sun-synchronous orbit.

How many of the above statements is/are correct?

a)    One

b)    Two

c)    Three

d)    None

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