Linked Questions

4 votes
4 answers
7k views

Mars looks like a blur

I took my telescope out tonight (I am new, just got the telescope a few days ago, it's my first one) and I was observing Mars, however all I see is just an bright orange circle, with no surface detail,...
Krystian S's user avatar
9 votes
4 answers
1k views

Where exactly is the modification that first corrected the spherical aberration in Hubble's primary mirror?

The April 2015 CBS News article How NASA fixed Hubble's flawed vision - and reputation describes the modification taken to the Hubble Space Telescopes by the Space Shuttle that was used to correct for ...
uhoh's user avatar
  • 30.7k
4 votes
2 answers
3k views

Why does this large Newtonian telescope's front cover have two or three holes in it?

The Michael Bernardo video How to use an Equatorial Mount for Beginners shows a large Newtonian telescope on an equatorial mount. The cover of the telescope's large aperture shows what looks like ...
uhoh's user avatar
  • 30.7k
7 votes
1 answer
1k views

How does the James Webb Space Telescope achieve a focal length of 131.4m?

How does the James Webb Space Telescope achieve a focal length of 131.4m ?
Sebastyen Laroche's user avatar
10 votes
2 answers
767 views

Why aren't secondary mirrors offset to get rid of diffraction spikes due to the support vanes?

Some kind of ellipsoidal shape mirror could reflect to a secondary mirror which is not in the way of the infalling light. Two advantages are immediately obvious. The primary mirror would not be partly ...
LocalFluff's user avatar
  • 11.4k
4 votes
1 answer
869 views

Under what situations can an aperture mask improve the resolution of a small/medium amateur telescope? Is this demonstrable mathematically?

@antlersoft's answer describes some of the challenges to seeing any details in the small disk of Mars in small amateur telescopes. In the case of reflecting telescopes, it mentions the use of either ...
uhoh's user avatar
  • 30.7k
3 votes
1 answer
369 views

Why is the Nancy Grace Roman Space Telescope's field of view shaped like a PacMan "ghost"?

The Curious Droid YouTube video NASA's Mega Hubble - The Roman Space Telescope illustrates the shape of the telescope's field of view and the outline has a smile or frown shape. For whatever reason it ...
uhoh's user avatar
  • 30.7k
2 votes
1 answer
187 views

Is there a reflecting telescope like as a Newtonian telescope but with a negative lens before the diagonal mirror?

A Cassegrain reflecting telescope contains a negative optical element between the main mirror and its focus. This increases it's focal length. Is there a reflecting telescope like as a Newtonian ...
Imyaf's user avatar
  • 301
4 votes
1 answer
168 views

Why does X-shooter use double passes through prisms for Echelle cross-dispersion instead of gratings?

The catchy title Down-the-barrel observations of a multiphase quasar outflow at high redshift: VLT/X-shooter spectroscopy of the proximate molecular absorber at z=2.631 towards SDSS J001514+184212 ...
uhoh's user avatar
  • 30.7k
1 vote
1 answer
131 views

Astrometry and Geometric Distortions

CCD's are widely used for astrometry. Since a spherical surface (the celestial sphere) is projected onto a rectangular surface, the plate scale or pixel scale (approximated with 1/focal length etc) is ...
Cheng's user avatar
  • 342