Astronomy and cosmology

Prelims

A total solar eclipse crossed Greenland, western Iceland, northern Spain, north eastern Portugal and northern Russia, Europe's first in 27 years and not seen from India. Totality is what makes such a track worth travelling to, because it is still the best way to see the Sun's corona from the ground.

• A solar eclipse happens only at new moon, when the Moon passes between the Earth and the Sun.
• The inner corona is too faint to see against the glare of the solar disc.
• A coronagraph blocks that disc artificially, but scattered light often spoils the view.
• Only in totality, seen from the narrow path of totality, does the Moon block the whole disc.
• The corona's magnetic field drives solar flares and coronal mass ejections, which disturb satellites, navigation and communications on Earth.

Prelims

Betelgeuse is a red supergiant in the constellation Orion whose brightness rises and falls on a six year cycle, for which there was no agreed explanation. Astronomers using the Very Large Telescope have found strong evidence of a close companion, named Betelgeuse B.

• The companion appears to be a young star of about 2.6 to 3.1 times the Sun's mass.
• It could explain the six year cycle, because it periodically blocks part of the star's light.
• A second observation is awaited to confirm the finding.

Prelims

The National Aeronautics and Space Administration (NASA) launched the Nancy Grace Roman Space Telescope on 30 August, to survey dark energy, dark matter and exoplanets. Most of what it is sent to measure cannot be seen at all, which is why it carries two instruments rather than one.

• It works from Lagrange Point 2, as the James Webb Space Telescope does, while Hubble orbits the Earth.

Prelims

Dark matter is detected only through its gravitational pull, so a proposal about what it is has to be tested by what it would do to things already visible. One such thing is a star that has finished burning and is still there.

• An Indian study proposed that ultra heavy dark matter captured inside a dead star could collapse into a tiny black hole that swallows it.
• It looks at millisecond pulsars and white dwarfs, where dark matter falling in outweighs what the black hole loses to Hawking radiation.
• Many such stars have lasted billions of years, which rules out dark matter that would have destroyed them sooner.

Prelims

The Indian Astronomical Observatory at Hanle in Ladakh, at 4,517 metres, is run remotely from Bengaluru by the Indian Institute of Astrophysics and gives more than 250 usable nights a year with very little water vapour.

See also: The Hanle Dark Sky Reserve