def METHOD_NAME(ts):
    t = ts.tt_jd(api.T0)
    eph = api.load('de421.bsp')
    boston = eph['earth'] + Topos('42.3583 N', '71.0636 W')
    b = boston.at(t)
    star = api.Star(ra_hours=[1.0, 2.0], dec_degrees=[+3.0, +4.0])
    p = b.observe(star)
    assert p.position.au.shape == (3, 2)
    assert p.velocity.au_per_d.shape == (3, 2)
    assert p.t.shape == (2,)
    assert (p.t.tt == api.T0).all()
    a = p.apparent()
    a1 = b.observe(api.Star(ra_hours=1.0, dec_degrees=+3.0)).apparent()
    a2 = b.observe(api.Star(ra_hours=2.0, dec_degrees=+4.0)).apparent()
    assert (a1.position.au == a.position.au[:,0]).all()
    assert (a2.position.au == a.position.au[:,1]).all()