Astronomy is a very wide field, from studying the beginning of the universe 13.8 billion
light years away to studying solar flares and sun storms only 1 astronomical unit away.
And in the heart of all the science in astronomy, lies different types of telescopes helping
astronomers observe different objects.
So let’s find out what these types are and what makes them unique in the world of astronomical
observations:
One way to classify telescopes is by their location, on the ground VS in space.
So we have ground-based telescopes, those that are stationed and operated from Earth
like the Keck telescope, the Magellan Telescopes and the Lowell observatory.
Ground-based telescopes have to be built at high altitudes, preferably on mountaintops
to provide the perfect environment for observation.
Mountaintops provide a couple of benefits for observation:
1.
They’re away from all the light pollution unlike cities where light pollution is at
its maximum.
2.
Mountaintops at high altitudes have less atmosphere, which means clearer sky for observation and
less atmospheric distortion.
And then we have space-based telescopes, those that are stationed in space and operated from
Earth like the Hubble space telescope and the Kepler space telescope, and those have
the advantage of being above Earth’s atmosphere thus producing better images that are not
distorted by the atmosphere.
On the other hand, ground-based telescopes produce blur images due to what is called
“atmospheric distortion” and that
To adjust the quality of images and account for atmospheric distortion, ground-based telescopes
have to have a set of equipment called “adaptive optics”
Now, you might ask, if space-based telescopes avoid the atmospheric distortion, and therefore
produce better quality images, then why not use them all the time instead of ground-based
ones?
Will space-based telescopes make ground-based telescopes obsolete?
Well, of course no!
And I have a couple of reasons to convince you why astronomers will always need ground
based telescopes: 1.
The cost, it took NASA and the European Space Agency ESA $ 1.5 billion to deploy the Hubble
space telescope in orbit, and then an extra $ 50 million to fix a faulty mirror that was
discovered only a couple of months after hubble was launched.
so the cost of fabricating and operating telescopes is astronomically higher (pun intended) when
they’re in space than when they’re on the ground.
2.
Maintenance flexibility, if we have a faulty mirror or a problem in the electronic circuit
of a ground based telescope, it’s somehow easy to solve, just ship the faulty equipment
back to the fabrication factory to have it fixed.
But in space, things aren’t quite as flexible!
If something goes wrong with a space-based telescope like the hubble space telescope
for example, we have to send astronauts to fix the problem which is both risky for the
astronauts and costly for the space agency.
Furthermore, other space-based telescopes don’t even have the luxury of being fixed
once a problem arises, and that’s due to their higher orbit around the earth which
makes it impossible for crewed missions to reach them.
3.
Reliability, space-based telescopes are constantly in danger of being bombarded by space junk
or tiny space debris, which puts more effort on engineers to design protective layers for
the telescope and its mirrors, which again costs more money.
However, ground-based telescopes are more reliable and far away from any space hazards,
protected under their dome from any dust particles or storms in Earth’s atmosphere.
4.
Competence, astronomers around the world write proposals to obtain observation time on telescopes
all around the world.
And when it comes to proposal acceptance for time on space-based telescopes, the competition
is sure higher.
The hubble space telescope for example has an acceptance rate of 0.2!
Yes you heard right!
Only 2 proposals of each 10 submitted are approved!
Another way to classify telescopes is by looking at the optical range they detect, which basically
means the kind of light the telescope is able to see.
Not all telescopes can see all kinds of light, just like humans only see one kind of light
that is the visible light, telescopes can also see one or 2 kinds of light.
The light spectrum is HUGE!
It has so many ranges extending from gamma rays to visible light to radio waves and a
punch of other ranges in between.
Fortunately, astronomers have different telescopes “seeing” different ranges to help them
do different kinds of science.
And before you get all jumpy asking why we need to “see” in all the ranges, I have
just the answer for you.
See, light is information and even though it may seem as if visible light has all the
information we need to identify an object, other ranges of light also contain vital information
and equally as important to study that object.
For example, infrared light gives us information about the temperature of the object, which
is otherwise impossible to obtain from visible light, and
gamma rays give us information about how energetic the object is.
Radio waves on the other hand give us information on things like the cosmic microwave background
radiation which is the radiation left over from the big bang that was first detected
and mapped using radio wave astronomy.
So, let’s take a look at different telescopes observing in different ranges, and let’s
start with everyone’s all time favourite telescope; the hubble space telescope.
The Hubble space telescope is special because it observes in a wide optical range from the
ultraviolet to the infrared, which means it helps astronomers study the same object in
more than one range of light which provides deeper insights into the comprehension of
the object.
For example, in the year 1995 Hubble took this picture of the Eagle nebula publicly
known as the Pillars of Creation that is 7000 light years away, the picture was taken in
visible light viewing gas and dust and the fine outlines of the nebula itself in addition
to its chemical composition.
Then later in 2020, scientists wanted to reviste the Pillars of Creation again but now using
a different optical range, so they pointed hubble to the Eagle nebula and it took this
picture in infrared light showing more extraordinary details that weren't before visible such as
the enormous number of stars that are now obvious in the background.
Some of the biggest discoveries Hubble gave us was to help astronomers in precisely calculate
the hubble constant which determines the rate of the universe’s expansion, as well as
keeping track of the growth of many galaxies across time.
Hubble also had a legacy in helping scientists to measure for the first time the atmospheric
composition of an exoplanet.
Some other telescopes are not as lucky as hubble and can only observe in one optical
range, just like the Spitzer Space Telescope that sees light in the infrared range only.
NASA deployed the Spitzer Space Telescope in the year 2003 and it was expected to last
only for five years, but it surprised everyone with more than 16 years in operation, to be
shut down only in January of this year.
Studying the universe in infrared light is so important because we can see exclusive
footage of things like stars in the beginning of their formation period, the location of
dust and baby stars in galaxies, material falling into supermassive blackholes, among
many other events and objects.
Since Earth’s atmosphere filters infrared light, astronomers had to have a space-based
telescope inorder to do infrared astronomy, and that’s where the Spitzer Space Telescope
comes in.
One of the biggest discoveries of the Spitzer Space Telescope was the observation of 7 earth-like
planets around a single star back in 2018, a discovery that took spitzer and astronomers
more than 500 hours of observation!
Another big hit by spitzer is providing astronomers with more than 2 million images to compile
an extensive map of our milky way galaxy back in the year 2013.
The images provided by Spitzer were taken over the course of more than 10 years!
And the map helped scientists to detect an extra amount of carbon in the galaxy than
predicted and it continues to drive new science today.
Now, let’s take a look at another type of telescopes that observe only the X-ray range
of light, and as an example we’re gonna discuss the
Chandra X-ray observatory, that's a space-based telescope launched by NASA into space back
in the year 1999 and expected to last only 5 years, but surprisingly, Chandra is still
alive and giving till today.
Observing light in the X-ray region is important because it helps astronomers study high energy
events like matter falling so close into the event horizon of blackholes, X-ray pulsars
around neutron stars, and extremely hot gas clouds that go up to hundreds of millions
of degrees which otherwise will not be visible.
The Chandra X-ray observatory made lots of great discoveries together with another X-ray
observatory called the XMM-Newton developed by the European Space Agency ESA.
Data collected from both helped astronomers measure the spin of dozens of blackholes by
observing how far the cloud of gas around each blackhole is.
And both Chandra and XMM-Newton helped astronomers understand the nature of X-ray background
radiation when they both produced an image of the sky’s background X-ray radiation
back in 2016.
Chandra and XMM-Newton also have a hit in the field of exoplanets, they both collected
data that led to better understanding of star- planet interactions like the data from the
system HD 17156 when the observatories noticed a flare from the star whenever its hot jupiter
planet passed by.
Furthermore, Chandra is constantly monitoring the supermassive blackhole in the center of
our milky way galaxy.
Now since we talked about different types of telescopes, let’s run quickly on some
of the most awaited telescopes coming in the future.
The Lynx X-ray observatory is a NASA space-based telescope still in the making, it will observe
the sky in X-ray and will be the successor of the Chandra X-ray observatory.
The Lynix observatory will be 100 times more powerful than the chandra observatory which
will allow it to observe objects more than 10 times further away.
The Lynix observatory is supposed to help astronomers better understand the nature of
the earliest blackholes formed in the universe and the evolution of galaxies, as well as
the births and deaths of stars.
And of course, we can’t talk about future telescopes without mentioning the James Webb
space telescope, a telescope made in collaboration between NASA, ESA, and the canadian space
agency.
The James Webb space telescope will observe light in the infrared region and is supposed
to be the successor of the Hubble Space Telescope.
You might have heard all the fuzz around the James Webb space telescope and how its deployment
keeps getting delayed and the frustration of astronomers.
Despite how you might think that NASA is a big fan of delaying missions, it’s not without
its reasons.
Missions typically get delayed because of bad weather on launch day or extra checkups
that have to be done.
In the case of the James Webb space telescope, every single detail has to be checked and
rechecked, there’s no room for error.
And that’s because there’s no chance for future checkups or servicing missions like
in the case of the Hubble space telescope.
And that’s because the James Webb space telescope will not be placed in a low Earth
orbit around the Earth like hubble, rather, it will be placed in what is called a lagrange
point which is a point 1.5 million km away from earth, away from the reach of any current
or future crewed missions to perform modifications or checkups.
We don't yet know when exactly the James Webb space telescope will be launched, but it’s
scheduled for some time in 2021.