salutations celestial sight seers i'm david fuller from eyes on the sky. eta cassiopeiae sometimes
just called eta cas is an interesting star in that it is one much like our own sun and yet it
offers some differences too. on the one hand it is similar to ours in that it is also a yellow-white
G-spectral class star with a mass 97 of the sun's, a radius a mere one percent larger,
and a temperature at 5,973 kelvin- that's only 200 degrees hotter than our sun's 5778 kelvin.
and at 19 light years away - a small cosmic step - it is like looking at a near twin of our sun. but
the difference is that eta cass has a companion star. indeed it is a double that revolves
around the primary every 480 years. while the companion is close in spectral type as a yellow
k-class star, the lower temperature of 4000 kelvin is because it contains far less mass
and therefore has a far lower luminosity - that is to say it's a lot dimmer for us. that means
there is a more obvious color difference than we might otherwise see if we looked at these stars
farther apart than they are to each other in the sky. more on that in a moment.
to find eta cassiopeiae look for the W or M shape of the constellation cassiopeia in the northern
sky. if you're not sure where to look for it check out my shapes in the sky cassiopeia video for how
to find it a link to that is in the description of this video. We are going to look for the star at
the top of the M on the left side which is shedar located here in the constellation and the center
star at the bottom known as navi located here. it's easy to find these as they are the stars on
the brighter side of the constellation. the stars on the other side of the M are slightly dimmer.
with a magnified finderscope center the star shedar in your wider field of view
and prepare to move it so that both shedar and navi are contained within the field
somewhat like this. they are less than five degrees apart
so both should fit within a typical seven degrees finderscope field of view like this.
hopefully if your finder is good quality and skies are dark enough you will notice three other
not quite as bright stars between them. two are somewhat dimmer and closer together but we want to
center the brighter star that is eta cassiopeiae. if not use the next method i will describe.
for telescopes with a red dot finder simply aim the red dot about
one third of the way from shedar towards navi like this with a long focal length eyepiece.
eta cassiopeiae should be in the field of view
as always start with low magnification to center the object first. and with this star
the separation between the two stars is only 11 arcseconds. this can be split with nearly
any telescope of 60 millimeters aperture or more but use magnification of 75 to 150 times power or
greater if your telescope will allow to cleanly split the two stars. and now that you have that
view what do you see? what colors are visible to you? one way to enhance the color of these stars
is to move the stars slightly out of focus so they're a bit enlarged in size but still bright.
do you see the yellow and orange? maybe white and deep yellow? something else? for more information
on that as well as sketches of what you can expect to see at the eyepiece visit the telescopes on the
sky section of eyes on the sky dot com and look for object number two eta cas in the catalog.
if you liked this video and it helped you find this object successfully check out
the other 39 telescopes on the sky objects. i'll lead you step by step to the best and
easiest objects to find from the northern hemisphere. and don't forget to subscribe to
this channel by clicking the subscribe button just below this video to the right on youtube
i make regular updates on how to find all kinds of interesting objects in the night sky
with binoculars telescopes and occasional reviews too
and have since 2010 thanks for watching i'm david fuller wishing you clear and dark skies