Aditya-L1's VELC produces Doppler images that show which way solar eruptions travel
In one line: Software developed at the Indian Institute of Astrophysics turns data from Aditya-L1's VELC into Doppler velocity images of the solar corona, showing whether solar plasma, including CMEs, is moving towards or away from Earth.
Published 21 October 2026. Written by Pratidin from the reports linked at the end; every fact checked by a separate review before publishing. How we work
India's solar mission Aditya-L1 has produced Doppler velocity images of the Sun's corona, the hot outer atmosphere, using its Visible Emission Line Coronagraph (VELC), The Hindu reported. The images show whether coronal plasma is moving towards or away from the observer, and so reveal the direction in which coronal mass ejections (CMEs) travel along the Sun-Earth line. Dr. V. Muthupriyal and her team at the Indian Institute of Astrophysics (IIA), Bengaluru, developed the software that processes VELC's data into these images. The technical details have been published in the Astrophysical Journal after peer review, and the processed images will be shared with the global scientific community.
The images rest on the Doppler effect: light from plasma moving towards an observer shifts to shorter wavelengths, and light from plasma moving away shifts to longer ones. VELC, one of Aditya-L1's seven payloads, is a coronagraph that blocks the Sun's bright disc and also splits the corona's light into a spectrum. It records three emission lines of highly charged iron, at 5303 Å, 7892 Å and 10747 Å. The report said VELC is "currently unique in its capability to generate such spectroscopic images in the visible wavelength range." CMEs are massive clouds of plasma that can disrupt satellites and communication systems, so their direction matters for space weather forecasting.
Aditya-L1, India's first space-based solar mission, was launched on 2 September 2023 and placed in a halo orbit around the Sun-Earth Lagrange point L1, about 1.5 million km from Earth, on 6 January 2024. In December 2024 ISRO reported a VELC result: observations of a CME on 16 July 2024, in which plasma was found moving away from the observer at about 10 km/s. The instrument team has also noted limits: the 5303 Å channel gives usable data, while the other two spectral channels are currently too noisy for science use.
Prelims facts
- Aditya-L1's VELC has produced Doppler velocity images of the solar corona that show whether plasma is moving towards or away from Earth.
- The processing software was developed at the Indian Institute of Astrophysics, Bengaluru, which also built VELC.
- VELC observes iron emission lines at 5303 Å, 7892 Å and 10747 Å; the 5303 Å channel currently gives the usable data.
- Aditya-L1 was launched on 2 September 2023 and has been in a halo orbit around L1, about 1.5 million km from Earth, since 6 January 2024.
Quick recall
- What does VELC stand for?
- Visible Emission Line Coronagraph
- Which institution built VELC and its Doppler software?
- The Indian Institute of Astrophysics, Bengaluru
- When was Aditya-L1 launched?
- 2 September 2023
- When did Aditya-L1 reach its halo orbit around L1?
- 6 January 2024
- How far is L1 from Earth?
- About 1.5 million km
- How many payloads does Aditya-L1 carry?
- Seven
- Which VELC emission line currently gives usable science data?
- 5303 Å, from highly charged iron (Fe XIV)
- What does a positive Doppler velocity mean in VELC images?
- Plasma moving away from the observer
Prelims practice question
With reference to the Aditya-L1 mission, consider the following statements:
1. It is placed in a halo orbit around the Sun-Earth Lagrange point L1.
2. Its Visible Emission Line Coronagraph was built by the Indian Institute of Astrophysics.
3. It carries a single payload.
Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer
Answer: (a) 1 and 2 only. Statement 1 is correct: it reached a halo orbit around L1 on 6 January 2024. Statement 2 is correct: VELC was built by IIA, Bengaluru. Statement 3 is incorrect: Aditya-L1 carries seven payloads.
Use this in UPSC Mains: previous-year questions
Recurring theme: India's space science missions and their uses
- How to use this
Cite Aditya-L1's VELC as an indigenous space science achievement with a practical use: forecasting solar storms that threaten satellites and communication.
- Aditya-L1, launched on 2 September 2023, orbits the Sun-Earth L1 point about 1.5 million km away.
- Its IIA-built VELC produces Doppler images showing whether coronal mass ejections move towards or away from Earth.
- Processed images will be shared with scientists worldwide, supporting space weather forecasts that protect satellites.
Aditya-L1 is another success in unmanned missions, though the question's focus is human spaceflight.
Mains practice question
What are coronal mass ejections, and why does knowing their direction matter? Explain how Aditya-L1's VELC contributes to space weather forecasting. (150 words)
Model answer
Coronal mass ejections (CMEs) are huge clouds of magnetised plasma thrown out from the Sun's corona. In October 2026, Aditya-L1's VELC produced Doppler images that show their direction of travel.
Why direction matters
- Earth-directed CMEs can disrupt satellites, communication systems and navigation.
- In ordinary coronagraph pictures, a CME moving towards Earth and one moving away can look alike.
VELC's contribution
- Doppler imaging: shifts in iron emission lines, such as 5303 Å, show plasma speed along the Sun-Earth line.
- Indigenous capability: VELC and its software were developed at the Indian Institute of Astrophysics; the method is published in the Astrophysical Journal.
- Vantage point: a halo orbit around L1, about 1.5 million km away, gives an uninterrupted view of the Sun.
- Open data: processed images will be shared with scientists worldwide.
- Limits: only the 5303 Å channel gives usable data now.
VELC adds an Indian input to global space weather forecasting.
The basics
Why this matters
The Sun sometimes throws out huge clouds of charged gas called coronal mass ejections (CMEs). If one heads towards Earth, it can disturb satellites, radio links and power grids. Knowing early whether a CME is coming towards us or going away is the heart of space weather forecasting. India's solar observatory, Aditya-L1, now produces images that help answer exactly that question.
Where Aditya-L1 sits
Aditya-L1 is India's first space-based solar mission. It was launched on 2 September 2023 and placed in a halo orbit around the Sun-Earth Lagrange point L1, about 1.5 million km from Earth, on 6 January 2024. From there it watches the Sun without interruption. See Lagrange points and halo orbits.
- 2 September 2023Aditya-L1 launched by ISRO
- 6 January 2024Placed in a halo orbit around L1
- 16 July 2024VELC observes a CME on the Sun's west limb
- December 2024VELC results on the onset of a CME published
- October 2026Doppler velocity images of the corona reported
The instrument
The Visible Emission Line Coronagraph (VELC), built by the Indian Institute of Astrophysics (IIA), Bengaluru, is one of seven payloads. A Coronagraph blocks the Sun's bright disc so that the faint outer atmosphere, the corona, can be seen. VELC also splits the corona's light into a spectrum. It records three emission lines from highly charged iron: 5303 Å, 7892 Å and 10747 Å.
- 1ImagingPictures of the corona in visible light at 5000 Å, from 1.05 to 3 solar radii
- 2SpectroscopySpectra of three iron emission lines from 1.05 to 1.5 solar radii
- 3SpectropolarimetryMeasures polarisation at 10747 Å to study magnetic fields
- 4Doppler imagingConverts line shifts into maps of plasma speed towards or away from the observer
How a Doppler image works
When a light source moves towards you, its waves are squeezed and the line shifts slightly to the blue; when it moves away, the line shifts to the red. This is the Doppler effect. By measuring the shift at every point, the IIA team's software makes a map of how fast the corona's plasma is moving along the Sun-Earth line. A CME moving towards Earth and one moving away look similar in a normal picture, but not in a Doppler image.
- Line shifts to shorter wavelength (blueshift)
- Negative Doppler velocity
- An Earth-directed CME candidate
- Line shifts to longer wavelength (redshift)
- Positive Doppler velocity
- Less threat to Earth
Why it is a first
According to the report, VELC is "currently unique in its capability to generate such spectroscopic images in the visible wavelength range." The processing method has been published in the Astrophysical Journal, and the images will be shared with scientists worldwide.
Go deeper
Why it matters for UPSC
It is a GS3 space technology and Indian achievement story, with Prelims hooks on Aditya-L1, Lagrange points, CMEs, coronagraphs and the Doppler effect.
The core idea
Aditya-L1 sits near L1, explained in Lagrange points and halo orbits. Its VELC is a Coronagraph that also measures spectra. Using the Doppler effect, the shift of a spectral line reveals the line-of-sight speed of plasma, which tells forecasters which way Coronal mass ejections are heading.
Numbers and dates to remember
- 2 September 2023: Aditya-L1 launched.
- 6 January 2024: halo orbit around L1, about 1.5 million km from Earth.
- 7: number of payloads; VELC is built by IIA, Bengaluru.
- 5303 Å, 7892 Å, 10747 Å: VELC's three iron emission lines.
- 1.05 to 3 solar radii: VELC's imaging field.
Where to go next
- Coronal mass ejections: what they are and why they matter for Earth
- Doppler effect: how a shift in light reveals speed
- Lagrange points and halo orbits: why Aditya-L1 sits where it does
- Coronagraph: how to see the corona without the Sun's glare
Go deeper: from pictures to forecasts
What is new. Most coronagraphs take pictures, which show a CME spreading in the sky plane but cannot tell its motion along the line of sight. VELC adds spectroscopy close to the Sun's edge, and the Doppler effect converts line shifts into speeds. The report calls VELC "currently unique" in its capability to produce such spectroscopic images in visible light.
Earlier results. In December 2024 ISRO reported VELC observations of a CME on 16 July 2024. The 5303 Å line showed the region dimming by about 50%, a temperature rise of about 30%, and plasma moving away from the observer at about 10 km/s, suggesting the CME was deflected by the Sun's magnetic field.
Limits. The instrument paper notes that the 5303 Å channel gives usable data, while the 7892 Å and 10747 Å channels are currently too noisy for science use. Doppler images show only the speed along the line of sight, so they work best with images from other angles.
Why it matters. Coronal mass ejections can damage satellites and disturb communication. From its spot near L1, explained in Lagrange points and halo orbits, Aditya-L1 watches the Sun without breaks, and its Coronagraph data, now openly shared, adds an Indian input to global space weather work.
Coronal mass ejections
What they are and why they matter for Earth
In one line: A coronal mass ejection (CME) is a huge cloud of magnetised plasma thrown out from the Sun's corona into space.
What happens
CMEs often occur with solar flares. If a CME reaches Earth, its magnetic field can interact with Earth's magnetic field and cause geomagnetic storms. These can disturb satellites, radio and navigation signals and power grids, and cause auroras.
Why direction matters
A CME that heads towards Earth is the one forecasters must warn about. In an ordinary coronagraph picture, a CME coming towards Earth and one moving away can look alike. VELC's Doppler images show the motion along the Sun-Earth line, which helps tell them apart.
Where to go next
Doppler effect
How a shift in light reveals speed
In one line: The Doppler effect is the change in the observed wavelength of a wave when its source moves towards or away from the observer.
How it works
A source moving towards you squeezes its waves, so light shifts to shorter, bluer wavelengths (blueshift). A source moving away stretches them, so light shifts to longer, redder wavelengths (redshift). The size of the shift tells the speed along the line of sight. The same effect changes the pitch of a passing ambulance siren.
Why it is in the news
VELC measures the shift of coronal emission lines, such as the 5303 Å green line of highly charged iron. A positive Doppler velocity means plasma moving away from the observer; a negative one means plasma moving towards it.
Where to go next
Lagrange points and halo orbits
Why Aditya-L1 sits where it does
In one line: Lagrange points are five positions in a two-body system, such as the Sun and Earth, where a small object can stay in a fixed position relative to both bodies.
How they work
At these points the gravity of the two large bodies balances the motion needed for the small object to move with them. L1 lies on the line between the Sun and Earth, about 1.5 million km from Earth. A spacecraft does not sit exactly at L1 but loops around it in a halo orbit.
Why it is in the news
From a halo orbit around L1, which it reached on 6 January 2024, Aditya-L1 has an uninterrupted view of the Sun, with no eclipses or night. That is why it can watch the corona continuously and track eruptions.
Where to go next
Coronagraph
How to see the corona without the Sun's glare
In one line: A coronagraph is a telescope that blocks the bright disc of the Sun so that its faint outer atmosphere, the corona, can be observed.
How it works
The corona is far fainter than the Sun's surface and is normally visible only during a total solar eclipse. A coronagraph creates an artificial eclipse inside the instrument. VELC is internally occulted: the central hole in its secondary mirror removes the light of the solar disc.
VELC in brief
VELC images the corona in visible light from 1.05 to 3 solar radii and takes spectra in three iron emission lines from 1.05 to 1.5 solar radii. It was built by the Indian Institute of Astrophysics, Bengaluru.
Where to go next
Take the 21 October 2026 quiz: 30 Prelims-style questions with answers