"Star clusters are small groups of stars huddled together in these images. They are bright, often white or blue. Bright stars often create a cross-hair shape because of the light overloading the Spitzer detectors, this is normal and you don't need to mark them."
I would change this to:
"Star clusters are small groups of stars huddled together in these images. They are bright, often white or blue. You might see them inside a bubble, or on their own. Bright stars often create a cross-hair shape because of the light overloading the Spitzer detectors, this is normal and you don't need to mark those shapes as anything unusual."
"Star clusters are small groups of stars huddled together in these images. They are bright, often white or blue. Bright stars often create a cross-hair shape because of the light overloading the Spitzer detectors, this is normal and you don't need to mark them."
I would change this to:
"Star clusters are small groups of stars huddled together in these images. They are bright, often white or blue. You might see them inside a bubble, or on their own. Bright stars often create a cross-hair shape because of the light overloading the Spitzer detectors, this is normal and you don't need to mark those shapes as anything unusual."