Astronomy Picture of the Day

Observatory / Course Archives / ASTR 110 Fall 2019 / Panzer

Uranus

Uranus is the seventh planet from the sun in our solar system. It is about four times the size of earth and its mass consist mostly of icy materials. Uranus's atmosphere is comprised mostly of hydrogen and helium. A small amount of methane in the planet's atmosphere gives Uranus its blue color because methane absorbs red light and reflects blue light. Uranus has a unique rotation as it rotates counterclockwise about its south pole instead of its north pole like most of the planets in the solar system. Voyager 2 flew by the planet in 1986 and verified that its south pole is tilted 98 degrees compared to its orbit. This means Uranus' south pole points almost directly at the sun.

The image above shows Uranus' two ring systems. The first sighting of the rings is debated. In the late 1700's, Sir William Herschel claimed to have discovered rings around Uranus. Because the rings are so faint, modern astronomers doubt his claim. The verified discovery of Uranus' rings belongs to astronomers James Elliot, Ted Dunham, and Jessica Mink. The inner rings are more easily visible and the brightest ring is named Epsilon. The outer rings of Uranus are comprised of dust particles left behind from collisions between Uranus' moon Mab and meteoroids. Mab can be seen in the image below as a series of eight bright dots on the right side of the outer ring.

MyCn18 Nebula

The picture above shows MyCn18 Nebula, named after Margaret Mayall and Annie Cannon. A nebula is a cloud of dust and gas in space. Some are formed from the explosion of a dying star sending gaseous material into space. Other nebulae form stars as gas and dust gather together. This nebula is the result of an exploded sun-like star. When stars like our sun explode, they leave behind a small white dwarf star. You can see in the white dwarf in the middle of this nebula. Outer layers of the star's gas are spread into space, excited by the white dwarf's light, and emit the red, green, and blue colors below.

This picture is comprised of three different photos taken by Hubble. Photos taken in the light of ionized nitrogen show the red colors, hydrogen shows green, and doubly-ionized oxygen shows blue. The colors correspond to their respective gas. Astronomers believe the hourglass shape is caused by a stellar wind. The wind is expanding in a gas cloud that is denser at the equator than at the poles, causing the gas to spread farther away from the star at the poles and remain close to the equator.

ESO 510-G13

The above photo is a spiral galaxy, the same type of galaxy our Milky Way belongs to. Spiral galaxies are characterized by their three main features: a central bulge, spiral arms, and a halo. The bulge is densely populated sphere consisting mostly of older stars. The presence of older stars explains the yellow color of the bulge as yellow and red stars outlive blue stars. The spiral arms form a disk surrounding the bulge and contain dust, gas, and younger stars. The halo surrounds the bulge and part of the spiral arms. It is less dense than the bulge and contains older star clusters.

ESO 510-G13 showcases a unique warped shape when viewed edge on (which is fortunately our view of the galaxy from earth). The shape is likely the cause of ESO 510-G13 colliding with another galaxy and is in the process of swallowing it. When the two galaxies collided, their large physical objects likely did not collide. Rather, the cause of the warped shape is because the gravitational interactions of the galaxies disrupted the flat disk structure normal spiral galaxies have. As the galaxy ages, its centrifugal force and gravity will eventually flatten out the arms of this galaxy and it will appear normal again.