NASA has joined the celebrations for the Fourth of July, the United States' Independence Day, with some "celestial" fireworks.
The US space agency shared the pictures of four beautiful nebulae — Cat's Eye Nebula, NGC 2392, Helix Nebula, and the Ring Nebula.
The Fourth of July celebrates the passage of the Declaration of Independence by the Continental Congress on July 4, 1776, establishing the United States. Following the Declaration, 13 North American colonies were separated from Great Britain.
The Fourth of July is celebrated with fireworks because they signify national pride and patriotism. Fireworks have been part of Independence Day in the United States since the first celebration of the Fourth of July, in 1777.
The Cat’s Eye Nebula
The Cat's Eye Nebula was captured by NASA's Hubble Space Telescope. The image shows a bull's eye pattern of eleven or even more concentric rings around the Cat's Eye. The Cat's Eye Nebula appears bright along its outer edge because each 'ring' is actually the edge of a spherical bubble seen projected onto the sky.
The concentric shells make a layered, onion-skin structure around the dying star. The star had ejected its mass in a series of pulses at 1,500-year-intervals, according to NASA.
NGC 2392
NGC 2392 was earlier referred to as the "Eskimo Nebula". Astronomers William Herschel discovered the nebula in the year 1787. From the ground, NGC 2392 resembles a person's head surrounded by a parka hood. The Hubble Space Telescope captured an image of the nebula in 2000. It displayed gas clouds so complex that they are not fully understood.
NGC 2392 is a planetary nebula, and the gas seen in the nebula's image composed the outer layers of a Sun-like star only 10,000 years ago.
Strong winds of particles from the central star inject filaments that are present in the interior. According to NASA, the outer disk of the nebula contains unusual light-year long orange filaments.
Helix Nebula
A star expands when it runs out of fuel, and subsequently, its outer layers puff off. Then, the core of the star shrinks, a phase known as a "planetary nebula". According to astronomers, the Sun is likely to turn into a planetary nebula in about five billion years.
NASA created an image of the Helix Nebula using infrared data from the Spitzer Space Telescope (green and red), optical light from Hubble (orange and blue), ultraviolet from NASA's Galaxy Evolution Explorer (cyan), and Chandra's X-rays (appearing as white). The X-rays show the white dwarf star that formed in the centre of the nebula. The Helix Nebula is about four light years across.
The Ring Nebula
The Ring Nebula or Messier 57 (M57) is a planetary nebula, and has a tiny white dot in its centre which is the star's hot core. It is called a white dwarf. The Ring Nebula, about 2,000 light-years away in the constellation Lyra, is best observed during August.
M57 was discovered by the French astronomer Antoine Darquier de Pellepoix in 1779, has an apparent magnitude of 8.8, and can be observed using moderately sized telescopes.
Astronomers imaged the Ring Nebula using the Hubble Space Telescope. The blue gas in the centre of the Ring Nebula is a football-shaped structure, and pierces the red, doughnut-shaped material. The nebula also has dark, irregular knots of dense gas, which can be seen along the inner rim of the ring. These gases have not yet been blown away by stellar winds. In the image, the knots and tails appear like bicycle spokes.
The deep blue seen in the centre of the nebula represents helium, the light blue colour of the inner ring represents the glow of hydrogen and oxygen, and the reddish colour of the outer ring is due to nitrogen and sulphur.