Astronomers estimate that there are more than 2 trillion galaxies in the universe we can observe alone! One of the most enjoyable things for amateur astronomers is searching for and observing distant and beautiful galaxies whose light has gone through millions or even billions of years before it is finally captured by telescopes on Earth. In the exciting search, we not only satisfy our curiosity about science, but also feel a pure reverence for the universe.
In today's astronomy, much of astronomers' job is to process and analyze large amounts of observational data, so it is often necessary to write and run programs that process images of the sky. One of the downsides of this approach is that we don't always experience the "hands-on" pleasure of exploring and observing every inch of the universe. Still, with powerful online tools, we can also observe galaxies that only a few people have seen so far.
Galaxies are within reach
Just a few decades ago, astronomers often had to go through long, cold, and lonely all-night observations before continuing to do the tedious task of examining photographic negatives. In the 21st century, with the development of technology, we can already access information anytime, anywhere through the Internet.
Now, automated telescopes and sky survey observations provide astronomers with so much data that machines are needed to assist with further analysis. In some cases, the human eye only looks at what computers think is interesting, while vast amounts of data are stored on the Internet for free, waiting for people to discover and appreciate.
Go online and find an atlas of the universe
AladinLite (https://aladin.cds.unistra.fr/AladinLite/) is one of the most powerful online tools that can observe our universe through many different telescopes. Here, we can scan the entire sky, look for hidden galaxies, and even decipher information about the evolution of their star populations.
Next, let's start looking for one of the most spectacular galaxies, the Wheel Galaxy. On the AladinLite interface, you can search for the common name of a celestial body, such as "cartwheel galaxy" (wheel galaxy), or known coordinates. The object's position will then be in the center of the interface.
The first image of the wheel galaxy we see is an optical image from the Digital Sky Survey (DSS2). The color of the image we see represents the different filters in the telescope. However, these are typical images of galaxies that we can see with the naked eye.
A common rule of thumb for astronomers is that differences in "color" within galaxies are due to differences in physical environment. It's worth noting that objects that look blue (with shorter wavelengths) are generally hotter than objects that look red (with longer wavelengths).
In this wheel galaxy, the outer ring looks bluer than the red part in the middle. This may imply that star formation and stellar activity occur in the outer ring, and less so in the center of the galaxy.
To confirm a hypothesis about star formation, we can choose observations of different wavelengths. When young stars form, they emit large amounts of ultraviolet radiation. Changing the sky survey to GALEXGR6/AIS, just looking at ultraviolet wavelengths, the results are very different: the entire central part of the galaxy seems to "disappear" from the image. This suggests that the region may be home to older stars with less active star formation.
We can find the results of 20 sky survey projects on TheRadinLite, which provide optical, ultraviolet, infrared, X-ray and gamma-ray sky imaging. When searching for interesting galaxies in the universe, you can start with an optical survey to find the galaxy of interest, and then use other survey surveys to observe how the image changes at a specific wavelength.
Search for other interesting galaxies
Now that you've learned to search for galaxies quickly, let's start the game! You can spend hours exploring these incredible images and finding galaxies that look interesting. If you need to zoom in further, it is recommended that you look at the DECalS/DR3 image for the highest resolution and detail.
The best way is to drag the Sky Atlas, and if you find something interesting, you can learn about it by selecting the target icon and clicking on the object.
Next, let's take a look at some of the most characteristic galaxies.
Spiral galaxies: Typically have a spiral-shaped disk structure that rotates around a center with large spiral arms that curve outward from a denser central region. This type of galaxy is very beautiful, and the Milky Way we are in is a spiral galaxy.
Elliptical galaxies: Mostly featureless, more "flat" than spiral galaxies, with stars sometimes forming almost a three-dimensional elliptical structure. Stars in these types tend to be older and less active in star-forming regions than spiral galaxies.
Lenticular Galaxy: Looks like a cosmic pancake with a bright central nucleus surrounded by an expanded disc-like structure that is fairly flat and featureless in the night sky. Such galaxies can be thought of as the "middle" type of spiral and elliptical galaxies. Most star formation in the lens galaxy has stopped, but there is still a lot of dust. (Ren Tian)