M31: The Andromeda Galaxy

At approximately 2.5 million light-years away, the Andromeda Galaxy, or M31, is our Milky Way's largest galactic neighbor. The entire galaxy spans 260,000 light-years across - a distance so large, it took 11 different image segments stitched together to produce this view of the galaxy next door.

The bands of blue-white making up the galaxy's striking rings are neighborhoods that harbor hot, young, massive stars. Dark blue-grey lanes of cooler dust show up starkly against these bright rings, tracing the regions where star formation is currently taking place in dense cloudy cocoons. Eventually, these dusty lanes will be blown away by strong stellar winds, as the forming stars ignite nuclear fusion in their cores. Meanwhile, the central orange-white ball reveals a congregation of cooler, old stars that formed long ago.

When observed in visible light, Andromeda's rings look more like spiral arms. The ultraviolet view shows that these arms more closely resemble the ring-like structure previously observed in infrared wavelengths with NASA's Spitzer Space Telescope. Astronomers using Spitzer interpreted these rings as evidence that the galaxy was involved in a direct collision with its neighbor, M32, more than 200 million years ago.

Andromeda is so bright and close to us that it is one of only ten galaxies that can be spotted from Earth with the naked eye. This view is two-color composite, where blue represents far-ultraviolet light, and orange is near-ultraviolet light.

Image Credit: NASA/JPL-Caltech
Explanation from: https://www.nasa.gov/mission_pages/galex/pia15416.html

The star cluster Westerlund 2

Westerlund 2 is a giant cluster of about 3000 stars located 20 000 light-years away in the constellation Carina.

Hubble's near-infrared imaging camera pierces through the dusty veil enshrouding the stellar nursery, giving astronomers a clear view of the dense concentration of stars in the central cluster.

Image Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team
Explanation from: https://www.spacetelescope.org/images/heic1509c/

White Sea Urchin & Reef Urchin

Sea urchins or urchins, archaically called sea hedgehogs, are small, spiny, globular animals that, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. About 950 species of echinoids inhabit all oceans from the intertidal to 5000 m deep. The shell, or "test", of sea urchins is round and spiny, typically from 3 to 10 cm (1.2 to 3.9 in) across. Common colors include black and dull shades of green, olive, brown, purple, blue, and red. Sea urchins move slowly, and feed on mostly algae. Sea otters, starfish, wolf eels, triggerfish, and other predators hunt and feed on sea urchins. Their roe is a delicacy in many cuisines. The name "urchin" is an old word for hedgehog, which sea urchins resemble.

Tripneustes ventricosus

Tripneustes ventricosus, commonly called the West Indian sea egg or white sea urchin, is a species of sea urchin. It is common in the Caribbean Sea, the Bahamas andFlorida and may be found at depths of less than 10 metres (33 ft).

The test of the West Indian sea egg is dark in colour, usually black, dark purple or reddish brown, with white spines 1 to 2 centimetres (0.4 to 0.8 inches) long. The test can reach 10 to 15 centimetres (3.9 to 5.9 in) in diameter. It is often covered with pieces of seagrass, fragments of shell and other debris in a manner similar to the closely relatedTripneustes gratilla. These decorations are held in place by tube feet among the spines and are believed to provide protection from the intense sunlight that penetrates the shallow water.

Echinometra viridis

Echinometra viridis, the reef urchin, is a species of sea urchin in the family Echinometridae. It is found on reefs in very shallow parts of the western Atlantic Ocean and the Caribbean Sea.

The reef urchin has an elliptical reddish brown test (shell) covered with medium length spines. These are greenish in colour with paler bases and darker, often violet, tips. This urchin grows to a diameter of 5 centimetres (2.0 in) with the longest spines being 3 centimetres (1.2 in). It looks very similar to the rock-boring urchin Echinometra lucunter, but the dark tips and the greater length of the spines are distinctive.

Image Credit & Copyright: Nick Hobgood
Explanation from: https://en.wikipedia.org/wiki/Tripneustes_ventricosus and https://en.wikipedia.org/wiki/Echinometra_viridis